th International Workshop on Solar Energy for … International Workshop on Solar Energy for Sustainability “Photosynthesis and Bioenergetics” 21 to 24 March 2016 Nanyang Executive

4th International Workshop on

Solar Energy for Sustainability

“Photosynthesis andBioenergetics”

21 to 24 March 2016 Nanyang Executive Centre,

Nanyang Technological University

Institute of Advanced StudiesSchool of Biological SciencesSolar Fuels Lab (School of Materials Science & Engineering and Energy Research Institute @ NTU)

Local Organising Committee

Members: Susana GEIFMAN SHOCHAT SBS, NTU Leong Chuan KWEK IAS, NTU Joachim LOO MSE, NTU Hwee Boon LOW IAS, NTU Maria-Elisabeth MICHEL-BEYERLE SPMS, NTU

Chair: James BARBER FRS Imperial College London & MSE, NTU

Co-Chair: Kok Khoo PHUA IAS, NTU

Peter PREISER SBS, NTUDaniela RHODES FRS SBS, NTUSubbu VENKATARAMAN MSE, NTUYang ZHAO MSE, NTU

To celebrate the 75th birthdays of Sir John Walker FRS and Leslie Dutton FRS

and the Life and Legacy of Jan Anderson FRS

INTRODUCTION

Global bioenergetics relies on the continuous input of solar energy initiating with light-driven charge separation and water splitting reactions of photosynthesis followed by the subsequent use of the resulting high energy electrons and protons to drive the production of ATP either through photosynthetic or oxidative phosphorylation. The resulting ATP is the energy currency of biology and powers the processes of life including the synthesis of organic molecules. These molecules are a store of chemical energy which is ultimately utilised by non-photosynthetic metabolism leading to their oxidation back to water and carbon dioxide from which they were formed.

This meeting will cover various aspects of this bioenergetic cycle to which Professor Sir John Walker (Nobel Laureate) FRS and Professor Leslie Dutton FRS have made major contributions and whose 75th birthdays will be celebrated. The cycle is initiated by the reactions of photosynthesis and the workshop will also cover the regulation of these processes in memory of the outstanding contributions made to this area of research by Professor Jan Anderson FRS who recently passed away. Therefore this workshop will bring together world leading scientists actively involved in understanding natural biological processes associated with the flow of energy in biological cells.

CONTENTS

Programme6

Speakers’ Abstracts13

Poster Session43

6

Programme

04:00 pm - 08:00 pm Pre-registration (Speakers only)

07:00 pm - 10:00 pm Social Reception @ Campus Clubhouse (Speakers only)

Pre-registration: 20 March 2016 (Sunday)

Day 1: 21 March 2016 (Monday)

08:00 am - 09:00 am Registration

09:00 am - 09:20 am Welcome address by Phua Kok Khoo (Director, Institute of Advanced Studies)

Opening address by Bertil Andersson (President, Nanyang Technological University)

Chair’s address by James Barber FRS (Imperial College London)

Morning SessionChairman: Bertil Andersson (NTU, Singapore)

09:20 am - 10:05 am John Walker FRS (Nobel Laureate, University of Cambridge, UK) Generation and regulation of rotation in ATP synthase

10:05 am - 10:50 am Leslie Dutton FRS (University of Pennsylvania, USA) Structure Engineering of Natural Solar Energy Conversion

10:50 am - 11:20 am Group Photograph and Coffee Break

11:20 am - 12:05 pm Rudy Marcus (Nobel Laureate, California Institute of Technology, USA) Rates, Equilibrium Constants and Bronsted slopes in F1-ATPase Single Molecule Imaging: Experiments and a Theoretical approach

12:05 pm - 12:50 pm Daniel Nocera (Harvard University, USA) The Artificial Leaf: From Sunlight + Water + Carbon Dioxide to Biomass and Liquid Fuel

12:50 pm - 01:35 pm Lunch

PROGRAMME

7

Programme

Afternoon Session Chairman: Leslie Dutton FRS (Philadelphia, USA)

01:35 pm - 02:20 pm Marten Wikstrom (Helsinki University, Finland) The Proton Pump of Cytochrome Oxidase - the Known and the Unknown

02:20 pm - 03:05 pm Peter Rich (University College London, UK) Mitochondrial cytochrome c oxidases: Functions of the Hydrophilic Channels and Supernumerary subunits

03:05 pm - 03:50 pm James Murray (Imperial College London, UK) Extensible Protein Scaffolds Based on Beta Solenoids

03:50 pm - 04:10 pm Coffee Break

04:10 pm - 04:55 pm Wolfgang Junge (University of Osnabrueck, Germany) Around Proton-Driven and Into Rotary ATP Synthase

04:55 pm - 05:40 pm Jasper van Thor (Imperial College London, UK) Femtosecond Infrared Crystallography of Photosynthesis: Watching Exciton Equilibration in Real Space

05:40 pm - 06:25 pm Marilyn Gunner (City University of New York, USA) Mechanisms for Generating Proton Transmembrane Gradients using Proton Pumps

06:40 pm Depart for Workshop Banquet Dinner

07:30 pm - 10:00 pm Dinner Banquet (by Invitation only)

Bus will leave from Nanyang Executive Centre, Guest Wing Lobby to Raffles Marina Club at 6.40pm for the dinner banquet.

After banquet, bus will leave for Nanyang Executive Centre, Guest Wing Lobby.

8

Programme

Day 2: 22 March 2016 (Tuesday)

Morning SessionChairman: John Walker (Nobel Laureate, University of Cambridge, UK)

09:00 am - 09:45 am James Barber FRS (Imperial College London, UK) Mn4CaO4 –cluster of the Oxygen Evolving Complex of Photosystem II

09:45 am - 10:30 am Judy Hirst (University of Cambridge, UK) Approaches to Determining the Mechanism of Catalysis by Respiratory Complex I

10:30 am - 10:50 am Coffee Break

10:50 am - 11:35 am Leonid Sazanov (The Institute of Science and Technology, Austria) Structure and Mechanism of Respiratory Complex I

11:35 am - 12:20 pm Neil Hunter FRS (University of Sheffield, UK) Native and Fabricated Membrane Protein Architectures for Energy Transfer and Trapping

12:20 pm - 01:05 pm General Discussion

01:05 pm - 01:50 pm Lunch

9

Programme

Afternoon Session Chairman: Daniel Nocera (Harvard, USA)

01:50 pm - 02:35 pm Werner Kühlbrandt (Max Planck Institute of Biophysics-Frankfurt, Germany) High-resolution cryoEM of Chloroplast and Mitochondrial ATP Synthase

02:35 pm - 03:20 pm Anthony Moore (University of Sussex, UK) Identification of the residues lining the ubiquinol-binding site of the alternative oxidases using novel site-specific inhibitors


03:40 pm - 04:25 pm Alison Telfer (Imperial College London, UK) The use of different chlorophylls to extend the spectrum of light energy capture and storage during photosynthesis

04:25 pm - 05:10 pm Fraser Armstrong (Oxford University, UK) A new mechanism for [NiFe]-hydrogenases, and its wider implications

05:10 pm - 05:55 pm Sandor Volkan-Kacso (California Institute of Technology, USA) Theory of the angular modulation of ligand binding rates and equilibrium constants in F1-ATPase controlled rotation experiments

06:45 pm Depart for Dinner at President’s Lodge

07:00 pm - 09:30 pm Dinner at President’s Lodge (by Invitation only)

Bus will leave from Nanyang Executive Centre, Guest Wing Lobby to President’s Lodge at 6.45pm.

After dinner, bus will leave for Nanyang Executive Centre, Guest Wing Lobby.

10

Programme

Day 3: 23 March 2016 (Wednesday)

Morning SessionChairman: Marten Wikstrom (Helsinki University, Finland)

08:45 am - 09:30 am Alfred Rutherford FRS (Imperial College London, UK) Role of Bicarbonate in Photosystem II: a redox tuning-based regulation mechanism

09:30 am - 10:15 am Gary Brudvig (Yale University, USA) The Oxygen Isotope Effect of Photosystem II Unveiled

10:15 am - 10:35 am Coffee Break

10:35 am - 11:20 am Per Siegbahn (Stockholm University, Sweden) The critical steps in water oxidation and proton pumping

11:20 am - 12:05 pm Nicholas Cox (Max PIanck Institute for Chemical Energy Conversion - Mullheim, Germany) Activation of Nature’s water splitting catalyst: spin state as a marker for structure evolution

12:05 pm - 12:50 pm Nathan Nelson (Tel Aviv University, Israel) High-resolution structures of plant and cyanobacterial Photosystem I

12:50 pm - 01:40 pm Lunch

11

Programme

Afternoon Session Chairman: James Barber (Imperial College London, UK)(Session Dedicated to the memory of Prof Jan Anderson, FRS, FAA)

01:40 pm - 02:25 pm Bertil Andersson (Nanyang Technological University, Singapore) A Tribute to Jan Anderson

02:25 pm - 03:10 pm Eva-Mari Aro (University of Turku, Finland) Regulation of photosynthesis - towards cyanobacteria cell factories

03:10 pm - 03:55 pm Alexander Ruban (Queen Mary University of London, UK) Dynamic light harvesting membrane


04:15 pm - 05:00 pm Helmut Kirchhoff (Washington State University, USA) From Molecules to Membranes: Understanding the plasticity of plant photosynthetic membranes

05:00 pm - 05:45 pm Peter Nixon (Imperial College London, UK) Repair and the evolution of photosystem II

05:45 pm - 06:30 pm Wah Soon Chow (Australian National University, Australia) Towards quantification of the cyclic electron flux around Photosystem I in leaves

Closing Remarks

12

Programme

Day 4: 24 March 2016 (Thursday)

Organized tour of Singapore

10:00 am - 07:00 pm City Tour

Bus will depart from Nanyang Executive Centre, Guest Wing Lobby at 10.00am.

13

Speakers’ Abstracts

SPEAKERS’ ABSTRACTS

Author(s): Professor Bertil Andersson

Affiliation(s): Nanyang Technological University

Email of Presenter(s): [email protected]

Title: A Tribute to Jan Anderson

Abstract:Jan Anderson is sadly no longer with us. She passed away on the 28th of August last year after short period of illness. She had very much looked forward to attend this conference here in Singapore.

Jan Anderson was through several decades a leading profile in photosynthesis research in particular when it came to the organization of the thylakoid membranes and their dynamics in response to changing environmental conditions. Through the years, she produced numerous of classical papers, such as the classical review from 1975 on the Molecular Architecture of Photosynthetic membranes. At that time, I was a Ph.D. student in Sweden and that paper was highly inspirational to me. I met Jan for the first time at the 4th International Conference in Reading UK in 1977. I convinced her that I should come to Canberra as her post-doc and that actually happened in 1979. This was the start of very fruitful collaborations for many years to come.

Jan Anderson was a dedicated scientist that for 50 years made tremendous contribution to photosynthesis research. She became a Fellow of the Australian Academic of Science in 1987 and a Fellow of Royal Society in 1996.

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Author(s): Fraser Armstrong

Affiliation(s): Department of Chemistry, Oxford University


Title: A New Mechanism for [NiFe]-hydrogenases, and its Wider Implications

Abstract:Microbes contain highly active metalloenzymes called hydrogenases that enable them to use direct water/H2 interconversions to manage their metabolism. The two main classes, known as [FeFe]- and [NiFe]-hydrogenases, are products of convergent evolution: their genes are unrelated, yet they have important similarities in their active sites because they both contain CO, CN– and thiolates as ligands and a common minimal [Fe(CO)(CN)(RS)2] motif. The importance of hydrogenases for a renewable future lies in the inspiration they provide for the simplest and most fundamental molecular redox reaction that may enable us to store unlimited solar energy. In terms of electrocatalytic rates and efficiencies, the active sites of hydrogenases may rival or even exceed that of platinum, thereby proving that a future hydrogen economy could be based upon common elements, albeit dressed up in the right environment.

An important concept is that of the ‘frustrated Lewis pair’ (FLP) in which a base (B) and acid (A), sterically unable to form a direct dative bond, cleave a H2 molecule through an adduct of the type B:H+---H–:A. If A is a transition metal able to access three sequential oxidation states, a cycle can be set up and the FLP becomes a catalyst. Studies on [FeFe]-hydrogenases have led to the conclusion that H2 is formed or cleaved heterolytically at an FLP site comprising one of the Fe atoms (A) and a secondary amine (B) at the bridgehead of an azadithiolate ligand that bridges the two Fe atoms of the catalytic centre. We have recently proposed, based on a highly successful program of site-directed mutagenesis, that a similar mechanism applies for [NiFe]-hydrogenases, in which base (B) is an arginine guanidine group suspended as part of a canopy above the metal (A) atoms Ni and Fe. Our evidence has stemmed from our ability to genetically engineer the active-site canopy in Hydrogenase 1 from E.coli – in particular, replacing strictly-conserved arginine-509 by lysine to give an isostructural variant having just 1% of the native activity.

Mechanism of Hydrogen Activation by [NiFe]-hydrogenases. R. M. Evans, E. J. Brooke,

S. A. M. Wehlin, E. Nomerotskaia, F. Sargent, S. B. Carr, S. E. V. Phillips and F. A. Armstrong.

Nature Chem. Biol. 12, 46-50 (2016).

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Author(s): Eva-Mari Aro

Affiliation(s): Molecular Plant Biology, University of Turku, Finland


Title: Regulation of Photosynthesis - Towards Cyanobacteria Cell Factories

Abstract:Photobiological solar fuels have a potential to bring fundamental breakthroughs towards sustainable biofuels. They will be based on direct conversion of solar energy into fuels using raw materials that are inexhaustible, cheap and widely available. Our research towards these goals is based on constructing a cyanobacterium chassis (based on Synechocystis sp PCC 6803) that can efficiently convert solar energy into fuels and valuable chemicals, by functioning mostly as a catalyst with minimal accumulation of biomass. Development of such a photosynthetic chassis requires thorough knowledge about natural energy conversion and electron transfer mechanisms of the cyanobacterial chassis, their regulation in ever changing light conditions and potential for their re-design towards most efficient conversion of solar energy into useful target products. My presentation will focus on recently discovered regulation mechanisms of cyanobacterial photosynthetic light reactions and their role in development of Synechocystis cells as an efficient chassis for sustainable biofuel and chemical production.

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Author(s): Professor James Barber FRS

Affiliation(s): Imperial College London


Title: Mn4CaO4 – cluster of the Oxygen Evolving Complex of Photosystem II

Abstract:The oxygen in our atmosphere is derived and maintained by the water splitting process of photosynthesis. The enzyme which facilitates this reaction and therefore underpins virtually all life on our planet is known as Photosystem II (PSII). It is a multisubunit enzyme embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria.

Powered by light, this enzyme catalyses the chemically and thermodynamically demanding reaction of water splitting. In so doing, it releases dioxygen into the atmosphere and provides the reducing equivalents required for the conversion of carbon dioxide into the organic molecules of life and is the origin of the fossil fuels. During the past years fully refined structures of a 700 kDa cyanobacterial dimeric PSII complex has been elucidated by X-ray crystallography which has given the organisational details of the 19/20 subunits (16/17 intrinsic and 3 extrinsic) which make up each monomer and provided information about the position and protein environments of the cofactors involved in the absorption of light, charge separation and water splitting. In the case of the latter, a cluster of three Mn ions and a Ca ion which form a cubane structure with bridging oxygens plus a forth Mn ion linked by oxo bonds to the cubane, makes up the heart of the catalytic site. Surrounding the metal cluster are highly conserved amino acid side chains, of which 7 form direct ligands to the metals. The structure of the catalytic site has provided a framework to develop a mechanistic scheme for the water splitting reaction leading to dioxygen formation. Moreover it has provided a platform to mimic the natural enzyme in order create “artificial photosynthesis” technology to capture solar energy and store it in chemical bonds. Such solar fuel technology could play a significant role in elevating the daunting problem of increasing levels of carbon dioxide in the atmosphere due to fossil fuel combustion and the associated worry about global climate change. A challenge now legally recognised by 195 different counties at the recent COP21 conference in Paris.

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Author(s): Sahr Khan and Gary W. Brudvig*

Affiliation(s): Department of Chemistry, Yale University


Title: The Oxygen Isotope Effect of Photosystem II Unveiled

Abstract:Photosystem II (PSII) catalyzes sunlight-driven oxidation of water during photosynthesis, supplying nearly all the O2 in our biosphere. The photosynthesis 18O kinetic isotope effect (KIE) is used in global Dole-effect models to explain the isotopic composition of O2 in the atmosphere, but there is ambiguity in both the magnitude of the PSII 18O KIE, and its relevance to proposed water-splitting mechanisms. Here, we show that the 18O KIE of PSII is 1.002 ± 0.001 in thylakoid membranes and PSII membrane fragments when assayed under standard laboratory conditions, which is explained because plastoquinone exchange is the rate-limiting step during steady-state turnover of PSII. When this rate limitation is removed by using high quinone concentrations and low pH, the 18O KIE of 1.022 ± 0.003 associated with water oxidation is unveiled. The structure of the OEC and the mechanism of the water-oxidation reaction of PSII will be discussed in the light of the KIE data, biophysical and computational studies of native,site-directed mutated and inhibitor-bound PSII, inorganic chemistry and X-ray crystallographic information.

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Author(s): Wah Soon Chow

Affiliation(s): Division of Plant Science, Research School of Biology, The Australian National University


Title: Towards quantification of the cyclic electron flux around Photosystem I in leaves

Abstract:Spatially separated from Photosystem II (PS II), PS I performs a dual role of participating in linear electron flux through both photosystems and in a cyclic electron flux (CEF) around itself. CEF, with a proton-pumping efficiency of 2 H+/photon compared with 1.5 H+/photon in linear electron transport, is meant to augment ATP formation to meet the requirement of 3 ATP:2 NADPH for carbon assimilation, and to supply additional ATP for other processes such as repair of ongoing photodamage to PS II during photosynthesis. Further, CEF aids in the photoprotection of both photosystems, through boosting the ΔpH-dependent non-photochemical quenching of excitation energy and by simply confining electron flow around a physiological path of ferredoxin reduction so as to minimize the formation of reactive oxygen species. Given the importance of CEF, there is a need to quantify CEF in vivo under physiological conditions. However, since the discovery of CEF-driven ATP formation sixty years ago, there has not been any satisfactory method of quantifying the electron flux, owing to the absence of a net product.

Various methods of monitoring CEF are either qualitative or inapplicable to physiologically-relevant conditions. Currently, the best quantitative estimation of CEF seems to be given by the difference (ΔFlux) between the total electron flux through PS I (ETR1) and the linear electron flux (LEF) through both photosystems. Both ETR1 and LEF can be measured in leaf segments under identical steady-state conditions, in the same whole tissue. In glasshouse-grown spinach, ΔFlux is largely inhibited by antimycin A. which is reputed to inhibit the major cyclic path in higher plants. However, in low-light-grown Arabidopsis, ΔFlux measured in high light seems to be dominated by other electron fluxes such as charge recombination within PS I. Thus, deficiencies of this method still exist, and will be discussed.

References:Kou J, Takahashi S, Oguchi R, Fan D-Y, Badger M R and Chow W S (2013) Estimation of the steady-state cyclic electron flux around Photosystem I in spinach leaf discs in white light, CO2-enriched air and other varied conditions. Functional Plant Biology 40: 1018-1028

Kou J, Takahashi S, Fan D-Y, Badger MR and Chow WS (2015) Partially dissecting the steady-state electron fluxes in Photosystem I in wild-type and pgr5 and ndh mutants of Arabidopsis. Frontiers in Plant Science 6: 758.

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Author(s): Nicholas Cox,1,2 Vera Krewald,1 Marius Retegan,1 Frank Neese,1

Wolfgang Lubitz,1 Dimitrios. A. Pantazis1

Affiliation(s): 1Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim (Ruhr) Germany 2Research School of Chemistry, Australian National University, Acton ACT, Australia


Title: Activation of Nature’s water splitting catalyst: spin state as a marker for structure evolutiond

Abstract:Biological water oxidation is catalyzed by a tetramanganese-calcium cofactor. Its structure is not static but moves between an inactive configuration, as seen in the X-ray crystal structure of the resting state and an active configuration as inferred from high field EPR measurements (1). The two states are similar, but the latter requires the coordination of an additional water molecule, rendering all four Mn ions six coordinate. Importantly structural evolution of the cofactor can be correlated with its magnetic spin state. In the “inactive” configuration the cofactor adopts a low ground spin state whereas in the “active” S-states it instead adopts a high spin ground state (2). The intermediates which facilitate cofactor activation can be isolated and characterized. Chemical modeling, based on existing and recent spin state information gathered from EPR show that the cofactor’s structure is dynamic immediately prior to insertion of a water molecule (2). It is this structural flexibility that allows redox tuning of the cofactor and provides a means via which the solvent water can bind to the cofactor (3).

References:1. Cox N, Retegan M, Neese F, Pantazis DA, Boussac A, Lubitz W. (2014) Science 345:804-808

2. Krewald V, Retegan M, Neese F, Lubitz W, Pantazis DA, Cox N. (2016) Inorg. Chem. (Forum Article) In press

3. Retegan M, Krewald V, Mamedov F, Neese F, Lubitz W, Cox N, Pantazis DA. (2016) Chem. Sci. 7(1): 72-84

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Author(s): Zhenyu Zhao, Christopher C. Moser and P. Leslie Dutton*

Affiliation(s): The Johnson Research Foundation, University of Pennsylvania School of Medicine, Philadelphia, PA


Title: Structural engineering of Natural Solar Energy Conversion

Abstract:Natural photosynthesis starts with the picosecond transformation of light-energy into electronic charges separated between closely positioned chlorophylls. This is followed by nano-microsecond electron-transfer mediated charge-transfer that generates membrane electrochemical gradients en route to driving millisecond-second oxidative catalysis of water with bi-product O2 and reduction of CO2 for cellular metabolism. The challenges encountered in efforts to mimic this high efficiency biological process, done to facilitate first-principles understanding or for applications benefitting mankind, are commonly recognized as failures to comprehend evident protein and multi-component complexity or to engineer an atomic level mechanism in a non-polar membrane milieux. Here, prompted by experimental observations, we have pursued a computational application of Marcusian electron-tunneling expressions to construct a set of generalized models for all photosystems that reveals a remarkably straightforward structural engineering. At its heart is a chain of four or more closely positioned light/redox-active cofactors. Calculations show that this chain promotes picoseconds charge separation over several nanometers with direct charge recombination slowed to the hour timescale, producing near-unitary quantum yields as in natural photosystems. The free energy driving this charge separation proves minimal, no more than that required to suppress the reverse thermal repopulation of the light excited state with loss, into the milliseconds-seconds time required for catalysis, thereby yielding an optimal energy conversion efficiency. Contrary to findings with two cofactors, we find that four or more cofactor charge separation is not constrained to non-polar environments but proceeds without loss of efficiency on changing the environmental polarities to those typical of small water-soluble proteins. Moreover, the immensely slow direct charge recombination rate of the charge-separated state calculated in the linear form indicates considerable freedom to create non-linear arrangements of the cofactor chains. Indeed, that the charge separating chains of natural photosystems adopt a curved configuration may indicate that our models usefully reflect a structural engineering intrinsic to natural counterparts. This structural engineering is clearly novel and applicable in a wide choice of environments. But of these, the first-principles design of water-soluble manmade photosystems integrated into the genome of living microorganisms tailored solely for sustainable solar fuel production in a cytoplasmic compartment may prove to be the most efficient and beneficial.

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Author(s): Marilyn Gunner, Xiuhong Cai, Witold Szejgis

Affiliation(s): Physics Department, City College of New York, CUNY


Title: Mechanisms for generating proton transmembrane gradients using proton pumps

Abstract:The transmembrane electrochemical gradient fuels cell function. Coupled electron and proton transfers through transmembrane proteins form the gradient. The minimum design requirements for proton transfer from the high pH, N-side to low pH P-side of the membrane through proteins will be described in Photosystem II (PSII) and Cytochrome c oxidase (CcO). Molecular simulations using classical electrostatics and Monte Carlo sampling is used identify motifs that allow proteins to change proton affinity at specific sites without large conformation changes.

In PSII as water is oxidized in the Oxygen Evolving Complex (OEC) and protons are released to the lumen. Protons are added to the P-side because of the very low proton affinity of the product O2 and no transmembrane proton transport is needed. The coupling of proton release to the 4 stages of OEC oxidation prior to water oxidation will be discussed.

Cytochrome c oxidase carries out the reduction of O2 to water adding to the proton gradient by removing protons from the N-side and pumping them to the P-side. Pumping requires that the protein have several sites that change proton affinity through the reaction cycle and at lest two gates that can change conformation to allow or stop proton transfers. The sites that release protons as the OEC becomes oxidized prior to H2O oxidation and where the protons are bound as CcO accumulates electrons prior to O2 reduction will be identified. The location of gates that would block proton uptake from the P-side of the membrane in CcO will be described.

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Author(s): Judy Hirst

Affiliation(s): Medical Research Council, Cambridge, UK


Title: Approaches to determining the mechanism of catalysis by respiratory complex I

Abstract:Respiratory complex I (NADH:ubiquinone oxidoreductase) is essential for oxidative phosphorylation by mammalian mitochondria. It couples the oxidation of NADH by ubiquinone to proton transfer across the energy-transducing inner mitochondrial membrane, providing electrons for oxygen reduction and driving the synthesis of ATP. Mammalian complex I contains a total of 45 subunits (with a combined mass of 1 MDa) that are encoded on both the nuclear and mitochondrial genomes. Fourteen of these subunits are the conserved ‘core’ subunits that are sufficient for catalysis; their structures were determined in the bacterial enzyme and recapitulated in our 5 Å resolution structure of the mammalian complex determined by single-particle electron cryo-microscopy. Despite this structural knowledge the mechanism of energy transduction by complex I remains obscure. In this talk I will describe recent results from structure-function studies to determine the mechanism of respiratory complex I.

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Author(s): Cvetelin Vasilev1, Michaël L. Cartron1, Craig MacGregor-Chatwin1, William Wood1, Melih Sener2, Goutham Kodali3, P. Leslie Dutton3, Graham J. Leggett4, Matthew P. Johnson1, Klaus Schulten2, C. Neil Hunter1

Affiliation(s): 1Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK 2Beckman Institute for Advanced Science and Technology, 3Department of Biochemistry and Biophysics, Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania, USA. 4Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK


Title: Native and Fabricated Membrane Protein Architectures for Energy Transfer and Trapping

Abstract:The 3-D structures of light-harvesting (LH) and reaction centre (RC) complexes have revealed the internal arrangements of chlorophyll-protein complexes that foster efficient solar energy harvesting and charge separation. Atomic force microscopy (AFM) allows us to understand the next level of structural information, namely the supramolecular organization of individual complexes to form a ‘photosynthetic unit’. With regard to functional studies many spectroscopic approaches have measured the dynamics of excited states in individual LH complexes and in the whole antenna. The application of molecular genetics has created variants of proteins, pigments and whole assemblies that test our knowledge of solar energy trapping. Recently, computational models of whole membrane assemblies have been generated that predict energy transfer and trapping behaviour and identify desirable design motifs for artificial photosynthetic systems.

Given our ability to purify, characterise, alter and model the behaviour of energy trapping networks, we are now in a position to fabricate new 2-D molecular assemblies, forming new networks that provide new test-beds for controlling and corralling energy migration. Such an approach employs a variety of lithographic methods to direct the assembly of multi-component structures consisting of two, then three types of LH and/or RC complexes on a single surface to promote directed energy migration and trapping. Associated with this, various forms of microscopy are required for spectroscopic readout with acceptable spatial, spectral and time resolution. Finally, suitably robust biological, biohybrid and bioinspired molecules employing de novo designed maquette proteins and/or pigments have to be constructed.

This talk will present recent progress on AFM mapping and computational modelling of purple bacterial, cyanobacterial and plant membranes, and it will show how new surface chemistries and lithographic methods are being used for the ‘bottom up’ fabrication of integrated architectures for energy transfer and trapping.

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Author(s): Wolfgang Junge

Affiliation(s): University of Osnabrück


Title: Around Proton-Driven and Into Rotary ATP Synthase

Abstract:ATP synthesis by FOF1 is driven by protonmotive force (pmf). The efficiency of protonic coupling to and mechanical coupling within the ATP synthase is discussed.

In chloroplasts and mitochondria the coupling membrane is sharply folded and tightly packed. As a consequence proton pumps and the ATP synthase can be laterally segregated. Under steady proton flow between proton pumps and the ATP synthase the electric component of the pmf (Δψ) is almost loss-free transmitted whereas the entropic component (ΔpH) suffers lateral loss (quasi-electroneutral proton diffusion!). Nature’s constructs to minimize loss are discussed.

The proton-motor (FO) drives the chemical generator (F1) that makes ATP. Both are rotary steppers. They differ in symmetry, 8-15 (depending on the organism) versus 3(6). FO and F1 are mechanically coupled by a peripheral stator and a central rotor. The central rotor is elastically compliant whereas the stator is very stiff. The elastic compliance decouples the two steppers in kinetic detail but couples them with 100% efficiency in the time-average. Elastic torque transmission between FO and F1 is pivotal for high kinetic efficiency and structural robustness of FOF1. The structural basis for domain-compliance and -stiffness is discussed.

Ann.Rev.Biochem. 83(2015)631 / Biophys.J. 109(2015)975 / NComms 4103(2014) / Nature 459(2009)364

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Author(s): Helmut Kirchhoff

Affiliation(s): Institute of Biological Chemistry, Washington State University, Pullman, WA, USA


Title: From Molecules to Membranes: Understanding the plasticity of plant photosynthetic membranes.

Abstract:More than a billion years of evolution shaped and tuned thylakoid membranes to make photosynthetic energy conversion both efficient and robust in an often unpredictable changing nature. A key for the success of biological energy conversion is the capability of the photosynthetic machinery to respond dynamically on environmental changes. This flexibility is realized by environmentally-controlled structural alterations of thylakoid membranes that occur on three different length scales: at the molecular level (Å - few 10 nm), the meosocopic level (several 10 nm – several 100 nm), and the overall membrane level (μm)The talk surveys examples for structural alterations on all three levels gained over the last five years. In detail, for the molecular level, data on lipid-protein interactions will be presented that show the impact of highly abundant non-bilayer lipids for the structure and function of light-harvesting complex II. For the mesoscopic level, the significance of a supra-molecular reorganization in stacked grana thylakoids from disordered to highly ordered semicrystalline protein arrays will be unraveled. Finally, it will be demonstrated that dynamic swelling and shrinkage of the entire grana membrane system is a crucial structural alteration for the control of diffusion-dependent electron transport and the repair of photodamage photosystem II.

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Author(s): Werner Kühlbrandt

Affiliation(s): Max Planck Institute of Biophysics, Department of Structural Biology


Title: High-resolution cryoEM of chloroplast and mitochondrial ATP synthase

Abstract:ATP synthases convert the energy of the proton gradient across mitochondrial or chloroplast membranes into the chemical energy of ATP. The mechanism by which proton translocation through the membrane drives ATP synthesis, or how ATP hydrolysis generates a trans-membrane proton gradient, has been unresolved for decades, because the structures of a critical subunit in the membrane was unknown. Electron cryo-microscopy of ATP synthase dimers from algal and yeast mitochondria or of the monomeric chloroplast ATP synthase have now revealed a hairpin of long near-horizontal membrane-intrinsic α-helices in the a-subunit next to the c-ring rotor. The horizontal helix hairpin is a structural theme common to all rotary ATPases. The horizontal helices create a pair of aqueous half-channels in the membrane that provide access to the proton-binding sites in the rotor ring. These recent findings help to explain the highly conserved mechanism of ion translocation by rotary ATPases.

Reference:Allegretti, M., Klusch, N., Mills, D.J., Vonck, J., Kühlbrandt, W. & Davies, K.M. (2015). Horizontal membrane-intrinsic α-helices in the stator a-subunit of an F-type ATP synthase. Nature 521, 237-240.

Kühlbrandt, W. & Davies, K. (2016): ATP synthase: A new twist for an ancient machine. Trends in Biochemical Sciences, January 2016, Vol. 41, No. 1, p.106-116

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Author(s): Rudolph A, Marcus

Affiliation(s): Caltech Noyes Lab


Title: Rates, equilibrium constants and Bronsted slopes in F1-ATPase single molecule imaging: experiments and a theoretical approach

Abstract:In a study with Dr. Sandor Volkan-Kacso (1) a theoretical model of elastically coupled reactions is proposed for single molecule imaging and rotor manipulation experiments on F1-ATPase. Stalling experiments are considered in which rates of individual ligand binding, ligand release, and chemical reaction steps have an exponential dependence on rotor angle. These data are treated in terms of the effect of thermodynamic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. These relations, in turn, are modelled using a formalism originally developed to treat electron and other transfer reactions. During stalling the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using biochemical and single molecule data, including the torsional spring constant of the elastically compliant rotor-stator complex measured by Junge and coworkers, the dependence of the rate constant and equilibrium constant on the stall angle, as well as the Bronsted slope are predicted and compared with experiment. Reasonable agreement is found with stalling experiments for ATP and GTP binding. The model can be applied to other torque-generating steps of reversible ligand binding, such as ADP and Pi release, when sufficient data become available.

(1) Sandor Volkan-Kacso and Rudolph A. Marcus, PNAS, Oct. 19, 2015, doi:10.1073/ pnas.1518489112

28


Author(s): Anthony L. Moore1, Luke Young1, Benjamin May1, Tomoo Shiba2, Daniel Ken Inaoka3, Shigeharu Harada2 and Kiyoshi Kita3

Affiliation(s): 1Biochemistry and Molecular Sciences, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK. 2Department of Applied Biology, Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan 3Department of Biomedical Chemistry, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan 113-0033


Title: Identification of the residues lining the ubiquinol-binding site of the alternative oxidases using novel site-specific inhibitors.

Abstract:The alternative oxidases (AOX) are ubiquinol oxidoreductases which catalyse the four electron reduction of oxygen to water. The protein is ubiquitous amongst plants, also found in some agrochemically important fungi, protists and widespread amongst human parasites such as Trypanosoma brucei, Cryptosporidium parvum and Blastocystis hominis and opportunistic human pathogens such as Candida albicans. It should be noted that immunocompromised individuals are particularly susceptible to these opportunistic human diseases, and new drugs that are well tolerated and have clearly defined biochemical targets are therefore urgently required. Since AOX is absent from the human host there is growing support for this protein to be considered as a viable target for the treatment of trypanosomiasis, cryptosporidiosis and candidiasis. AOX is an integral interfacial monotopic protein that interacts with a single leaflet of the lipid bilayer and contains a non-haem diiron carboxylate active site. Crystal structures confirmed that AOX is a homo-dimer with each monomer being comprised of 6 long α-helices, 4 of which form a 4 helix bundle which acts a scaffold to bind the two iron atoms (connected by hydroxo bridge). The iron atoms within the active-site under oxidised conditions are co-ordinated by 4 glutamate residues but no histidine residues which is an unusual co-ordination for a diiron protein. The redox-active tyrosine is within 4Å of the active-site consistent with its proposed role in the oxygen reduction cycle. In addition to the wild-type enzyme, we have recently obtained high-resolution structures of the protein in the presence of a number of novel site-specific inhibitors. Such structures have revealed the presence of a hydrophobic channel that connects the diiron centre with the interior of the lipid bilayer and the nature of the residues involved in substrate/inhibitor binding. Site-directed mutagenesis confirms the importance of these residues for substrate orientation and enzyme activity. Results will be presented in terms of the nature of the ubiquinone-binding site and insights this has provided into the mechanism of oxygen reduction catalyzed by AOX.

29


Author(s): Murray,James

Affiliation(s): Imperial College London


Title: Extensible Protein Scaffolds Based on Beta Solenoids

Abstract:Protein design is in general hard, as beyond very small domains, the all-atom folding problem is intractable. To solve this, we propose an approach based on extensible repetitive scaffolds. The scaffold can be incrementally elaborated, allowing complexity to be built up in stages, without requiring large-scale all-atom design. The rigid scaffolds can also be used to design crystal lattices or closed point group assemblies. We have developed a series of scaffold proteins, Beta1, based on the RFR (repeat five residues) family of beta solenoid scaffolds. The initial scaffold protein was produced by drawing residues from an RFR frequency table, so the middle 120 residues have no evolutionary “memory”. We have solved the structures of length variants, and also produced scaffolds with loop elaborations from the central core. The loop structures have been designed using a novel de novo all-atom approach, rather than being assembled from fragments of known structure. The loops are folded in accordance with the original design. The potential of this approach to design will be discussed.

30


Author(s): Yuval Mazor, Anna Borovikova, Vinzenz Bayro- --Kaiser, Hila Toporik, Sigal Netzer- -- El, Daniel Klaiman, Daniel Nataf, Maya Antoshvili and Nathan Nelson

Affiliation(s): Department of Biochemistry,The George S. Wise Faculty of Life Sciences, Tel Aviv University


Title: High-resolution structures of plant and cyanobacterial Photosystem I

Abstract:Plant Photosystem I (PS I) is one of the most intricate membrane complexes in Nature. It is comprised of two complexes, a reaction center and light-harvesting LHCI. We developed a method for obtaining better mass spectroscopy data from membrane complexes. Using the corrected amino acid sequences an improved plant PSI structure was obtained. An atomic-level structural model of higher plant PSI at 2.8 Å resolution has been constructed based on new crystal form. The crystal belongs to P212121 symmetry space group, with one protein complex in each asymmetric unit. The structure includes 16 subunits and more than 200 prosthetic groups, the majority of which are light harvesting pigments. The model reveals detailed interactions, providing mechanisms for excitation energy transfer and its modulation in one of Nature’s most efficient photochemical machine.

An operon encoding PSI was identified in cyanobacterial marine viruses. We generated a PSI that mimics the salient features of the viral complex containing PsaJ-F fusion subunit. The mutant is promiscuous for its electron donors and can accept electrons from respiratory cytochromes. We solved the structure of the PsaJ-F fusion mutant as well as a monomeric PSI at 2.8 Å resolution, with subunit composition similar to the viral PSI. The novel structures provided for the first time a detailed description of the reaction center and antenna system from mesophilic cyanobacteria, including red chlorophylls and cofactors of the electron transport chain. Our finding extends the understanding of PSI structure, function and evolution and suggests a unique function for the viral PSI.

31


Author(s): Peter J. Nixon1, Shengxi Shao1, Jianfeng Yu1 and Josef Komenda2

Affiliation(s): 1Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom 2Institute of Microbiology, Center Algatech, Opatovický mlýn, 37981 Tŕeboň, Czech Republic


Title: Repair and the evolution of photosystem II

Abstract:It is now well established that the oxygen-evolving photosystem II (PSII) complex is a weak link in photosynthesis and that the reaction centre subunits, mainly the D1 polypeptide, are prone to irreversible damage by high light. To maintain PSII activity, a repair cycle operates to specifically replace the irreversibly damaged subunit within the complex by a newly synthesized copy. One remarkable aspect is the specificity of the process as only the damaged subunit is targeted for degradation. We have shown previously that a specific FtsH protease heterocomplex is required for selective degradation of damaged D1 in the cyanobacterium Synechocystis 6803 [1] and that this FtsH complex degrades damaged D1 in a highly processive reaction probably initiated at the N-terminus of D1 [2] with specificity achieved by access of the FtsH complex to damaged D1 by partial or complete detachment of the neighbouring CP43 subunit [3]. This model therefore suggests that efficient repair is promoted by maintaining D1 and CP43 as separate subunits in PSII rather than fusing them into a single larger reaction centre subunit as seen in the more stable PSI complex. To test this hypothesis we have constructed a mutant in which we have fused the N-terminus of D1 to the C-terminus of CP43. The resulting strain is still able to assemble active oxygen-evolving PSII complexes and can still grow photoautotrophically but is compromised in PSII repair. Overall our data indicate that efficient repair of PSII has selected for the maintenance of separate D1/CP43/D2/CP47 subunits during evolution.

References:[1] Boehm et al (2012) ‘Subunit organisation of a Synechocystis hetero-oligomeric thylakoid FtsH complex involved in Photosystem II repair’ Plant Cell 24, 3669-3683.

[2] Komenda et al (2007) ‘The exposed N-terminal tail of the D1 subunit is required for rapid D1 degradation during Photosystem II repair’ Plant Cell 19, 2839-2854.

[3] Krynická et al (2015) Accessibility controls selective degradation of photosystem II subunits by FtsH protease’ Nature Plants 15168

32


Author(s): Daniel G. Nocera

Affiliation(s): Harvard University, Department of Chemistry and Chemical Biology


Title: The artificial leaf: From sunlight + water + carbon dioxide to biomass and liquid fuel

Abstract:The artificial leaf accomplishes a solar fuels process that captures the elements of photosynthesis — the splitting of water to hydrogen and oxygen using light from neutral water, at atmospheric pressure and room temperature. The device, which comprises a silicon wafer coated with self-healing catalysts based on Mn, Co and Ni, is a buried junction where a photovoltaic material is protected from solution or “buried”. The buried junction PEC cell is free from many of the design limitations of a traditional PECs. We have advanced the design of the artificial leaf by utilizing the hydrogen from the artificial leaf an d translating with carbon dioxide to make liquid fuels. A bio-engineered bacterium has been developed to convert carbon dioxide, along with the hydrogen produced from the artificial leaf, into biomass and fusel alcohols. In this hybrid microbial | artificial leaf system, unprecedented solar-to-biomass (10.7%) and solar-to-liquid fuels (6.2%) yields have been achieved.

33


Author(s): Peter R. Rich

Affiliation(s): Institute of Structural and Molecular Biology, University College London


Title: Mitochondrial cytochrome c oxidases: functions of the hydrophilic channels and supernumerary subunits

Abstract:The core structures of bovine mitochondrial cytochrome c oxidase (CcO) and ‘A1-type’ forms of bacterial CcO are very similar. All contain two very similar hydrophilic networks of amino acids and waters termed the D and K channels. A third hydrophilic network, the H channel, is prominent in mitochondrial CcOs. This structure is also evident in bacterial forms, though with some notable differences. Several lines of evidence have suggested that mammalian mitochondrial CcO pumps protons through the H channel, which contrasts with the D channel route that they take in bacterial forms. Our analysis of coupling efficiencies of yeast mitochondrial CcOs with mutations in these potential proton pathways shows unequivocally that, at least in yeast mitochondrial CcO, pumped protons are transferred through the D channel. Nevertheless, homology modelling of the yeast CcO core structure reveals that a clear H channel structure is present, albeit with some differences in comparison to that of bovine CcO. This raises the question of what alternative function the H channel structure might have. I will review evidence that it may act as a ‘dielectric channel’ than can modulate core enzymatic activity through dielectric changes that affect heme a properties. Its properties may be influenced allosterically by changes in supernumerary subunits, providing a means of optimising core catalytic functions in different environments and tissues.

34


Author(s): Alexander Ruban

Affiliation(s): Queen Mary University of London


Title: Dynamic light harvesting membrane

Abstract:The emergence and evolution of life on our planet was possible owing to the Sun which provides energy to our Biosphere. All life forms need energy for existence and proliferation in space and time. Light energy conversion takes place in photosynthetic organisms that evolve in various environments featuring an impressive range of light intensities that span several orders of magnitude. This property is achieved by the evolution of mechanisms of efficient light harvesting that involved development of antenna pigments and pigment-protein complexes as well as the emergence of various strategies to counteract the detrimental effects of high light intensity on the delicate photosynthetic apparatus. In this talk I will focus on the mechanisms of light harvesting and photoprotection in photosystem II. The molecular mechanism of non-photochemical chlorophyll fluorescence quenching, NPQ, its regulatory factors and significance in protection of the reaction center from the photodamage will be in the focus of this talk. The outline of the major component of non-photochemical quenching, qE, is suggested to comprise four key elements: trigger (ΔpH), site (antenna), mechanics (antenna dynamics) and quencher(s). The current understanding of the identity and role of these qE components will be discussed. Involvement of protons, different LHCII antenna complexes, the PsbS protein and different xanthophylls will be outlined. The evidence for LHCII aggregation and macrostructural reorganization of photosystem II and their role in qE will be presented. The models describing the qE locus in LHCII complexes, the pigments involved and the evidence for structural dynamics within single monomeric antenna complexes will be discussed. I will present a scheme explaining how PsbS and xanthophylls may exert control over qE by controlling the affinity of LHCII complexes for protons with reference to the three major concepts of dynamic light harvesting membrane: hydrophobicity change, allostery and hysteresis (light memory). Finally, a new methodology for assessing the photoprotective effectiveness of qE will be introduced.

35


Author(s): K.Brinkert, S.de Causmaecker, A Krieger-Lizskaya, A. Fantuzzi and A.W. Rutherford

Affiliation(s): Department of Life Sciences, Imperial College London aIBiTEC, CEA Saclay, France


Title: Role of Bicarbonate in Photosystem II: a redox tuning-based regulation mechanism

Abstract:The role of bicarbonate in Photosystem II has been debated for many decades. It is known that bicarbonate removal slows down PSII activity and this was shown to be mainly due to slowed QA

-• oxidation and is associated with the bicarbonate being bound to the non-heme iron that is located symmetrically between the two sequential quinone acceptors, QA and QB. A role for the bicarbonate in the second protonation step forming QBH2 has gained some support. However it is not known why a slowing down of proton-coupled electron transfer should be beneficial, nor is there an explanation why PSII has an exchangeable carboxylate ligand to the iron rather than a non-exchangeable one, like the glutamate side-chain in the homologous, non-oxygenic reaction centre.

Here we show that bicarbonate binding controls the redox potential of QA, shifting it upon binding by -74mV. QA

-• formation results in the binding constant of the bicarbonate weakening by a factor of ~15. Thus over-reduction of the PQH2 pool (which occurs when photosynthesis is limited by substrate CO2 concentration) would result in the accumulation of QA

-•, and this would lead to release of bicarbonate. This would then result in an increase in the Em of QA/QA

-•, which would increase the energy gap between P+•QA

-• and P+•Ph-•, thereby disfavoring back-reactions by the chlorophyll triplet and 1O2 generating route. When CO2 (which is in equilibrium with bicarbonate) levels increase, the PQ pool would be re-oxidized, bicarbonate would rebind, and the QA/QA

-• Em and the QA-• forward electron

transfer rate both return to the normal functional levels.

This new regulatory model involves the final substrate in photosynthesis, CO2, feeding back on the first step in the photosynthetic electron transfer chain, PSII, slowing electron supply and protecting PSII itself from charge recombination-mediated photodamage.

36


Author(s): Leonid Sazanov

Affiliation(s): Institute of Science and Technology Austria


Title: Structure and mechanism of respiratory complex I

Abstract:NADH-ubiquinone oxidoreductase (complex I) is the first and largest enzyme in the respiratory chain of mitochondria and many bacteria. It couples electron transfer between NADH and ubiquinone to the translocation of four protons across the membrane. It is a major contributor to the proton flux used for ATP generation in mitochondria, being one of the key enzymes essential for life as we know it. Mutations in complex I lead to the most common human genetic disorders. It is an L-shaped assembly formed by membrane and hydrophilic arms. Mitochondrial complex I consists of 45 subunits of about 1 MDa in total, whilst the prokaryotic enzyme is simpler and generally consists of 14 conserved “core” subunits. We use the bacterial enzyme as a “minimal” model to understand the mechanism of complex I. We have determined first atomic structures of complex I, starting with the hydrophilic domain, followed by the membrane domain and, finally, the recent structure of the entire Thermus thermophilus complex (536 kDa, 16 subunits, 9 Fe-S clusters, 64 TM helices). Structures suggest a unique mechanism of coupling between electron transfer in the hydrophilic domain and proton translocation in the membrane domain, via long-range (up to ~200 Å) conformational changes. I will discuss our current work, which is aimed at elucidating the molecular details of the coupling mechanism through determination of structures of the complex in different redox states with various bound substrates/inhibitors, using both X-ray crystallography and new cryo-EM methods.

37


Author(s): Per Siegbahn

Affiliation(s): Stockholm University, Sweden


Title: Theoretical studies of photosystem II and cytochrome c oxidase

Abstract:A very high level of understanding of water oxidation in photosystem II has now been reached. Theoretically predicted structures of the S1, S2 and S3 states have during the past years been confirmed in detail by spectroscopy and high-resolution X-ray structures. A predicted mechanism for O-O bond formation between an oxyl radical and an oxo-group has also found strong spectroscopic support. The progress and remaining questions will be discussed.

Recent years has also seen a large progress on the understanding of proton pumping in cytochrome c oxidase. Since protons are both pumped and consumed, intricate gating mechanisms are required, and these have been suggested. Apparent long range effects will also be discussed and explained.

38


Author(s): Dennis J. Nuernberg, A. William Rutherford and Alison Telfer

Affiliation(s): Imperial College London, Department of Life Sciences, London SW7 2AZ, UK


Title: The use of different chlorophylls to extend the spectrum of light energy capture and storage during photosynthesis

Abstract:Until fairly recently it was thought that only chlorophyll a (Chl a) could provide a sufficiently oxidising potential to split water during the process of oxygenic photosynthesis. However, the discovery of the cyanobacterium, Acaryochloris marina, which has 98% Chl d and only a very low level of Chl a, has shown that Chl d, with an absorption maximum ~30 nm into the far red beyond that of Chl a, is also capable of powering water splitting. This demonstration has changed our views. Even more recently, Chl f, a third even longer wavelength absorbing chlorophyll has been discovered to be present in various cyanobacteria when they are grown under far red light. The antenna pigments are changed in order to utilise the long wavelengths available. Chl f only represents up to ~15% of the total Chl present in these cyanobacteria. We are currently investigating the role of Chl f in extending light energy capture and storage from the visible out into the far red.

39


Author(s): Marius Kaucikas1, Karim Maghlaoui1, Jim Barber1, Thomas Renger2 and Jasper J van Thor1*

Affiliation(s): 1Imperial College London, South Kensington Campus, Sir Ernst Chain Bld, United Kingdom. 2Johannes Kepler University at Linz, Institute of Theoretical Physics


Title: Femtosecond Infrared Crystallography of Photosynthesis: Watching Exciton Equilibration in Real Space

Abstract:We have performed structurally sensitive femtosecond time resolved infrared crystallography of oriented orthorhombic crystals of Photosystem II core complexes of Synechococcus elongates, which allows a real-space analysis of exciton dynamics and charge separation. Directional selection of both the visible excitation and the infrared probes prepares and measures populations which are analysed on the basis of X-ray crystallographic coordinates. Excited state chlorophyll a infrared absorption allows a real space probe of exciton dynamics in the local, single pigment, basis. Two contrasting models, known as the trap-limited and as transfer-to-the trap limited model are critically tested. The dichroic amplitudes that result from photoselection are maintained on the ~60 ps time scale that corresponds to the dominant energy transfer process which provides compelling evidence for the transfer-to-the–trap limitation of the overall light-harvesting process. On nanosecond time-scale non-crystallographic symmetry is developed for a structural measurement of the P680+/Pheo- charge separated state that supports the mode assignments for Pheo/Pheo- and P680/P680+ contributions.

40


Author(s): Sandor Volkan-Kacso and Rudolph A. Marcus

Affiliation(s): California Institute of Technology


Title: Theory of the angular modulation of ligand binding rates and equilibrium constants in F1-ATPase controlled rotation experiments

Abstract:We propose a dynamical model of elastically coupled nucleotide binding and release reactions for single molecule imaging and rotor manipulation experiments on F1-ATPase.[1] In stalling experiments individual ligand binding, ligand release, and chemical reaction steps show an exponential dependence on rotor angle. In the theory, these data are treated in terms of the effect of thermodynamic-elastic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. The relations are modeled using a formalism originally developed to treat electron and group transfer reactions, whereby the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using the torsional spring constant of the rotor-stator complex measured by Junge and coworkers as well as other biochemical and single molecule data, the rate and equilibrium constants versus stall angle are predicted and compared with experiment, without using adjustable parameters. Reasonable agreement is found with stalling experiments for ATP and GTP binding. Subsequently, using the same theory, I present the analysis of another single molecule experiment in which the rotor shaft is subject to slow controlled rotation. With a computational statistical method the bias due to finite experimental time resolution is removed and the unbiased rate versus rotor angles are reproduced and explained by the model.

41


Author(s): John E. Walker

Affiliation(s): MRC Mitochondrial Biology Unit, Cambridge CB2 0XY, UK


Title: Generation and regulation of rotation in ATP synthase

Abstract:The rotary action of ATP synthases is driven in one sense by the hydrolysis of ATP and in the other, when ATP is being synthesised, by the trans-membrane proton motive force. The rotation driven by hydrolysis has been studied extensively in “single-molecule” experiments [1], that has resolved the rotary cycle into 120o steps divided into sub-steps. Structural explanations have been provided of the 120o steps, but the molecular description of the sub-steps remains contentious [2]. However, with the realisation that bacterial and mitochondrial enzymes differ in the number and magnitude of their sub-steps, agreement is emerging, and a molecular explanation has been provided of how release of phosphate from the mammalian enzyme generates one 30o sub-step [3]. Until recently, a molecular explanation has been lacking of how the proton motive force drives rotation in the opposite sense, as there was no molecular description of the interface between the membrane domain of the rotor where the trans-membrane proton pathway is thought to lie. Important contributions to the provision of this description have come recently from both X-ray crystallographic [3] and electron cryo-microscopy studies [4,5] of various intact ATP synthases. They indicate that the proton pathway is provided by polar residues in trans-membrane α-helices in the a-subunit that are tilted at 30o to the plane of the membrane. Cardiolipin molecules that bind briefly to specific sites near to the exit of the pathway are likely to participate in the release of the protons [6]. The hydrolytic activities of ATP synthases from mitochondria, bacteria, and chloroplasts are regulated by different mechanisms [2]. They offer the opportunity of developing drugs that inhibit bacterial enzymes selectively, without effect on the human enzyme, that could be used to combat the resurgence of infectious bacterial pathogens.

References:1. R. Yasuda, H. Noji, M. Yoshida, K. Kinosita, H. Itoh (2001) Resolution of distinct rotational substeps by submillisecond kinetic analysis of F1-ATPase. Nature 410:898–904.

2. J.E. Walker, The ATP synthase: the understood, the uncertain and the unknown, Biochem. Soc. Trans. 41 (2013) 1–16. doi:10.1042/BST20110773.

3. E. Morales-Rios, M.G. Montgomery, A.G.W. Leslie, J.E. Walker, Structure of ATP synthase from Paracoccus denitrificans determined by X-ray crystallography at 4.0 Å resolution., Proc. Natl. Acad. Sci. USA. 112 (2015) 13231–6. doi:10.1073/pnas.1517542112.

4. M. Allegretti, N. Klusch, D.J. Mills, J. Vonck, W. Kühlbrandt, K.M. Davies, Horizontal membrane-intrinsic α-helices in the stator a-subunit of an F-type ATP synthase, Nature. 521 (2015) 237–40. doi:10.1038/nature14185.

5. A. Zhou, A. Rohou, D.G. Schep, J. V. Bason, M.G. Montgomery, J.E. Walker, et al., Structure and conformational states of the bovine mitochondrial ATP synthase by cryo-EM, ELife. 4 (2015). doi:10.7554/eLife.10180.

6. A.L. Duncan, A.J. Robinson, J. E. Walker. Cardiolipin binds selectively to conserved lysine residues in the rotors of metazoan ATP synthases. To be submitted.

42


Author(s): Mårten Wikström

Affiliation(s): University of Helsinki


Title: The Proton Pump of Cytochrome Oxidase - the Known and the Unknown

Abstract:It will soon be 40 years since the discovery of proton pumping by the terminal enzyme of the mitochondrial respiratory chain, cytochrome oxidase. During this time remarkable achievements have been made using time-resolved and static spectroscopic and electrometric techniques, by X-ray crystallography, and more recently by computational approaches that have included both molecular mechanics and quantum chemical methodology. As a result we have a good picture of how the enzyme catalyses the reduction of O2 to water, both with regard to the underlying structural changes in the bimetallic heme/copper active site, as well as the dynamic rate parameters. The principles of linking these events to proton translocation are also fairly well understood, although some details of how the pathways of proton transfer function are still unknown.

43

Poster Session

POSTER SESSION

Poster 1

Author(s): Bemgba Bevan Nyakuma

Affiliation(s): Centre of Hydrogen Energy, Institute of Future Energy, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru Malaysia.

Email of Presenter(s): [email protected], [email protected]

Title: Bioenergy potential of Typha spp in Nigeria

Abstract:Typha spp is a wetland grass crop native to countries in the Northern Hemisphere. It is typically described as a very prolific, hardy, fast growing and dominant competitor of wetlands. In Nigeria, the prevalence of Typha spp been attributed for the increased incidence of Quelea birds, spread of crop diseases, loss of soil nutrients and low crop yields. The plant has also been known to aggressively distort the natural biodiversity of plant and animals species. These attributes present significant challenges to farmers resulting in increased costs and challenges of managing weeds, diseases and water on farmlands. As a result, scientists and policy makers are searching for novel techniques and innovative technologies to address the menace of Typha spp and its threat to the livelihood of many wetland farmers. One promising approach for eliminating the menace of Typha spp potentially involves the valorization of the plant into biofuels. With high crop yields of over 22 Mg/ha (leaves) and 31 Mg/ha (rhizomes), Typha spp is a potentially practical, renewable and sustainable solid biomass feedstock for clean energy fuels. Consequently, this paper seeks to explore the potential of Typha spp for bioenergy applications. It will examine and highlight promising techniques and technologies for the efficient valorization of Typha spp into biofuels. In addition, it will explore the potential challenges and proffer recommendations on the most practical methods of creating a bio-refinery and bioenergy economy based on Typha spp. Lastly, the paper will review current literature on the utilization of Typha spp and highlight the most promising routes for managing the menace and preventing the spread of the plant in Nigeria.

44

Poster Session

Poster 2

Author(s): Gurudayal, Michael Graetzel, Nripan Mathews, Lydia Helena Wong

Affiliation(s): MSE, NTU


Title: Highly Efficient Perovskite- Hematite Tandem Cells for Unassisted Solar Water Splitting

Abstract:Photoelectrochemical water splitting with semiconducting photoelectrodes has received much attention but unassisted water splitting driven by a single photoelectrode has remained elusive due to rigorous electronic and thermodynamic requirements. Employing a tandem cell wherein the total photovoltage produced by complementary optical absorption across different semiconducting photoelectrodes is a possible pathway to unassisted overall light induced water splitting. Low photovoltages generated by conventional photovoltaic materials (eg. Si, CIGS) has limited such systems typically consist of double or triple junction design which increases the complexity due to optoelectrical trade-offs and are also not cost effective. Here we demonstrate a single solution processed organic-inorganic halide perovskite (CH3NH3PbI3) solar cell in tandem with a Fe2O3 photoanode can achieve overall unassisted water splitting with a solar to hydrogen conversion efficiency of 2.4%. The performance of hematite photoanode has been improved by the Mn doping and Copi photoelectrochemical deposition. To understand the fundamental limitations of Fe2O3 photoanode intrinsic solar to chemical conversion efficiency of the doped and undoped Fe2O3 photoanodes were estimated. The total photopotential generated by our tandem system (1.87V) exceeds both the thermodynamic and kinetic requirements (1.6V), resulting in overall water splitting without the assistance of an electrical bias. Our recent efforts are improved the STH efficiency by 3.5%, which is the highest efficiency reported ever with single junction PV-PEC tandem cell.

45

Poster Session

Poster 3

Author(s): Shao Haiyan, Soo Han Sen

Affiliation(s): CBC-SPMS-NTU


Title: Enhancing Electrocatalytic Hydrogen Evolution by Nickel Salicylaldimine Complexes with Alkali Metals in Aqueous Media

Abstract:The use of renewable energy for the electrocatalytic production of hydrogen gas from aqueous media, especially seawater, is an attractive solution for the generation of sustainable fuels. Currently, the electrocatalyst with the lowest overpotential and highest activity for the hydrogen evolution reaction is platinum, although a number of earth-abundant metal chalcogenides and phosphides come close. Nonetheless, most of the reported electrocatalysts function in organic solvents or under highly acidic aqueous solutions. We demonstrate that the introduction of non-coordinating ether functionalities on the periphery of an earth abundant salicylaldimine nickel complex enhances the electrolysis of proton reduction in the presence of alkali metal cations, including sodium ions found in seawater. The catalyst exhibits a huge increasement in hydrogen production rate with lithium ions in solution compared to the background. Based on the single crystal X-ray structure, we propose that the pendant ether arms steer alkali metal ions and water molecules in close proximity to the nickel active centre, which in turn provides higher proton concentrations during the catalytic cycle. We show that judicious selection of functional groups that target sodium ions can provide a viable approach to develop better electrocatalysts, which can produce hydrogen fuel from seawater.

46

Poster Session

Poster 4

Author(s): Chao Shen,1,2 Denis Fichou,2,3,4 and Qing Wang,1#

Affiliation(s): 1Department of Materials Science and Engineering, Faculty of Engineering, National University of Singapore, 117576, Singapore 2School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore 3Sorbonne Universités, UPMC Univ Paris 06, UMR 8232, Institut Parisien de Chimie Moléculaire, F-75005, Paris, France 4CNRS, UMR 8232, Institut Parisien de Chimie Moléculaire, F-75005, Paris, France


Title: Interfacial engineering for semiconductor-sensitized solar cells with 10-butyl-phenoxazine-2-carboxylic acid as a surface grafted molecular relay

Abstract:We report a new molecule, 10-butyl-phenoxazine-2-carboxylic acid (BPCA), to work as a relay in the semiconductor-sensitized solar cells employing a cobalt complex as electrolyte. BPCA is transparent in the visible light region, so there is almost no contribution to the photocurrent from the molecule itself. However, after BPCA grafting onto the semiconductor sensitizer, the efficiency and stability of the photovoltaic device are dramatically enhanced. It results from the excellent electron donating property of BPCA, which could help rapidly remove holes from the valence band of the semiconductor sensitizer after photo-excitation. This process facilitates the charge separation and thus stabilizes the sensitizer. With BPCA surface modification, both CdS/BPCA and CdSe/BPCA-sensitized TiO2 solar cells exhibit much enhanced Voc, Jsc and power conversion efficiency compared with those without any modification, when the cobalt bipyridyl complex is used as redox mediator.

47

Poster Session

Poster 5

Author(s): Imre Vass and László Sass

Affiliation(s): Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary


Title: Photosynthetic electron transport in silico

Abstract:We have developed a computer model network of electron transport components in the thylakoid membrane of photosynthetic organisms. The model provides an excellent tool to simulate electron transport processes in a wide range of conditions, and can be used to perform in silico experiments with special interest in the function of Photosystem II, Photosystem I, the NDH-1 complex, etc. The model was used to study the role of non-radiative charge recombination from the singlet radical pair 1[P680+Phe-] in regulating 1O2 formation in cyanobacteria. By comparing the model predictions with experimentally detected 1O2 production we demonstrated the photoprotective effect of enchanced non-radiative charge recombination in Photosystem II. We have also used the in silico photosynthesis model to interpret the recently described wave phenomenon in the relaxation of flash-induced Chl fluorescence in microalgae. Our results show that the fluorescence wave reflects changes in the redox level of the PQ pool caused by the imbalance of PSII and PSI electron transport and the feedback of electrons from stromal components to the PQ pool via the NDH-1 complex. A further application of the model is the study of the interaction of photosynthetic and metabolic electron transport with special emphasis on the kinetic changes of the NADPH pool under light-dark transitions.

48

Poster Session

Poster 6

Author(s): Mun Hon Cheah, Ron Pace, Rob Stranger, Fred Chow

Affiliation(s): Australian National University


Title: 18O enrichment revealed identity of Ws in S3 of Photosystem II

Abstract:Biological water oxidation occurs at a Mn4CaO5 cluster within Photosystem II. While the substrate exchange kinetics is well known, the identity of the substrates remains elusive. Here we report a novel scheme to determine the 18O/16O isotope ratio of evolved O2 during a single complete turnover cycle of Photosystem II (PSII). Results show substrate enrichment of 18O in the intermediate S3 state of PSII, relative to S1. Our analysis indicates that the substrate with slow exchange kinetics (Ws) is enriched in 18O. DFT calculations of model system revealed the identity of Ws to be consistent with a terminally bound water molecule in S3.

49

Poster Session

Poster 7

Author(s): Tiago Toscano Selão 1, Lifang Zhang 1, Jana Knoppová 2, Josef Komenda 2 and Birgitta Norling 1

Affiliation(s): 1 School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551 Singapore 2 Institute of Microbiology, Center Algatech, Opatovický mlýn, Novohradská 237, 379 81 Třeboň, Czech Republic


Title: Photosystem II assembly occurs in the thylakoid membrane of the cyanobacterium Synechocystis sp. PCC6803

Abstract:Thylakoid biogenesis requires timely synthesis, processing and assembly of protein, lipid and pigment components. Efficient photosystem II (PSII) assembly has a crucial importance in this process as its D1 subunit is particularly susceptible to photodamage and has a high turnover rate, particularly in high light.

PSII assembly is a modular process, with assembly steps proceeding in a specific order. We used aqueous two-phase partitioning to separate plasma membranes (PM) and thylakoid membranes (TM) in a Synechocystis sp. PCC6803 strain lacking CP47 and studied the subcellular localization of early assembly intermediates for PSII biogenesis. The early D1–D2 assembly complex and associated PSII assembly factors were thus shown to accumulate in TM.

Newly synthesized D1 (pD1) is inserted to TM with a C-terminal extension, which must be cleaved by the C-terminal processing protease CtpA for assembly of the oxygen-evolving complex. Following pD1 insertion and processing by radioactive pulse–chase labeling we showed that pD1 insertion and processing occurs only in TM, where epitope-tagged CtpA was also specifically localized.

However, other proteins proposed to be required for PSII/thylakoid biogenesis associate with PM. These results suggest that PSII assembly occurs in TM with interaction with PM needed for efficient PSII and thylakoid biogenesis.

50

Poster Session

Poster 8

Author(s): Lifang Zhang a, Tiago Toscano Selão a, Eva Selstam b and Birgitta Norling

Affiliation(s): a School of Biological Sciences, Nanyang Technological University, Singapore; b Umeå Plant Science Center, Umeå, Sweden


Title: Localization of carotenoids biosynthesis in Synechocystis sp. Pcc6803

Abstract:Carotenoids play important roles in light harvesting, photoprotection and membrane structural organization. Their biosynthesis is described to a great extent but localization of the different enzymatic steps is still unclear. We studied the carotenoid composition of different membranes of Synechocystis sp. PCC6803 as well as the localization of some of the key carotenoid biosynthesis enzymes so as to understand their role in thylakoid membrane (TM) biogenesis and complex assembly.

Using sucrose gradient and aqueous two-phase partitioning, we isolated three membranes from Synechocystis. Carotenoid composition (by HPLC) showed that the “light” plasma membrane (PM1) has a high carotenoid:protein ratio, in comparison to the “heavier” plasma membrane (PM2) or TM. β-carotene dominates in PM1 and TM, while myxoxanthophyll is the major carotenoid in PM2. We studied the localization of epitope-tagged CrtQ and CrtO, two well-studied carotenoid synthesis enzymes and showed that both enzymes are locally more abundant in PM than in TM, implying that PM has higher synthesis rates of β-carotene precursors and echinenone. Though β-carotene plays very important roles in photosystem assembly, no direct interaction of these two enzymes with photosynthetic complexes could be identified. This data suggests a membrane organization model where carotenoids migrate from PM to TM through direct or dynamic contacts.

51

Poster Session

Poster 9

Author(s): Anthony Larkum

Affiliation(s): Plant and Global Climate Cluster, University of Technology Sydney, Broadway, NSW 2007 Australia


Title: Molecular Mechanisms for Coral Bleaching and prospects for Coral Reefs in the Future

Abstract:The global rise in sea surface temperatures causes regular exposure of corals to high temperature and high light stress, leading to worldwide disastrous coral bleaching events (loss of symbiotic dinoflagellates (Symbiodinium) from reef-building corals). The temperatures involved are ~ 30 C which would not normally be a problem but in corals or their symbionts, Symbiodinium sp., this leads to impairment of the photosystems. Over the last decade the evidence implicates effects on both photosystem II and photosystem I. Recent work seems to implicate reactive oxygen species (ROS) generation, first by the Mehler Ascorbate Peroxidase (MAP) pathway and then by PSII. Recently picosecond chlorophyll fluorescence experiments on cultured Symbiodinium Clade C cells exposed to coral bleaching conditions uncovered the transformations of the alga’s photosynthetic apparatus (PSA) that activate an extremely efficient non-photochemical “super-quenching” mechanism. The mechanism is associated with a transition from an initially heterogeneous photosystem II (PSII) pool to a homogeneous “spillover” pool, where nearly all excitation energy is transferred to photosystem I (PSI). There, the inherently higher stability of PSI and high quenching efficiency of P700+ allow dumping of PSII excess excitation energy into heat, resulting in almost complete cessation of photosynthetic electron transport. This potentially reversible “super-quenching” mechanism protects the PSA against destruction at the cost of a loss of photosynthetic activity. We suggest that the cessation of photosynthesis and the lack of organic carbon production (e.g. sugars) in the symbiotic Symbiodinium provide a trigger for the symbiont expulsion, i.e. bleaching.

52

Poster Session

Poster 10

Author(s): Joanna Sacharz and Alexander Ruban

Affiliation(s): School of Biological and Chemical Sciences, Queen Mary University of London, United Kingdom


Title: The role of PsbS in photoprotection

Abstract:PsbS, zeaxanthin and low lumen pH play essential roles in the photoprotective thermal dissipation of excess absorbed light energy in the light-harvesting antenna (LHCII) of PSII. However the details of the action of PsbS protein in the mechanism of qE-type non-photochemical fluorescence quenching (NPQ) are largely unknown. We optimized a novel pull-down assay combined with low concentration of selected membrane-permeable hydrophobic cross-linker for the isolation of stabilized protein interactions from intact chloroplasts. We report that PsbS in both spinach and Arabidopsis thaliana plants can be associated with Lhcb1-6 subunits. Our pull-down data suggests that PsbS is localized in the close proximity to LHCII M trimers prior to illumination and the formation of photoprotective state requires binding to minor antenna (mainly CP29 and CP26). Gold-labeling and analysis of PsbS positions in the thylakoid membranes demonstrate its arrangement into 30-50nm clusters in NPQ state. Interestingly, in the light-adapted chloroplasts containing zeaxanthin, the PsbS interactions were further promoted towards minor antenna complexes. In npq1 mutant with impaired zeaxanthin synthesis we registered abolished interactions with LHCII trimers and enhanced abundance of CP26 and CP24. Overall, our results demonstrate the importance of PsbS in LHCII antenna rearrangements leading to aggregation for NPQ formation and the modulatory role of zeaxanthin in PsbS-LHC interactions.

53

Poster Session

Poster 11

Author(s): A. Said*, Laila Saad, Yasmin. M. Yousry, and Ayman. M. Mohamed

Affiliation(s): Department of Materials Science, Institute of Graduate Studies and Research, Alexandria University, P.O Box 832, Egypt


Title: Graphene as a Counter Electrode in Dye sensitized Solar Cell (DSSC)

Abstract:Graphene is a promising material for fabrication of the counter electrodes in DSSCs due to its high electrical conductivity, high electrocatalytic activity and poisoning effect overcoming. In this work, the graphene was chemically prepared by the reduction of graphene oxide then the optimum preparation parameters of graphene were investigated. These parameters are the concentration of hydrazine monohydrate as a reducing agent, the time of the reduction process and the temperature of the reduction process. The prepared graphene was characterized by UV-visible spectroscopy, FT-IR, XRD and HRTEM. Then the performance of DSSCs with untreated and heat treated graphene as counter electrodes at different temperatures in nitrogen atmosphere were investigated. Also, the performance and photovoltaic parameters of DSSC with nanocomposite structure of graphene/Polyaniline (PANI)/graphite as a counter electrode were studied as well. The DSSC with heat treated graphene at 250 oC for 1 hr. in nitrogen gas atmosphere as a counter electrode had a better performance compared to DSSCs with untreated graphene as a counter electrode or with heat treated graphene at 250 oC for 1 hr. followed by heat treated at 400 oC for 15 min. as a counter electrode.

54

Poster Session

Poster 12

Author(s): Yasmin M. Yousry 1, Ayman M. Mohamed 2, Moataz M. Soliman 3

Affiliation(s): 1- PhD student, Mechanical Engineering Department, National University of Singapore (NUS), Singapore. 2- PhD student, Materials Science and Engineering, Nanyang Technological University (NTU), Singapore. 3- Professor of Electronic Materials, Department of Materials Science, Institute of Graduate Studies and Research, Alexandria, Egypt.


Title: Ruthenium Oxide as a New Buffer layer for Inverted Polymer Solar Cells

Abstract:The inverted polymer solar cell is more promising than the conventional structure of polymer solar cell by using a high stable high work function top electrode. Different solar cell structures were investigated in this study to observe the optimum performance parameters. Zinc Oxide (ZnO) nanoridges were used as electron acceptors and ruthenium oxide (RuO2) as a hole injection for the first time. The fabricated cells were characterized using scanning electron microscope to show the morphology of each layer in the cell and by UV-Vis spectroscopy. The performance of the prepared inverted polymer cells were evaluated by measuring current-voltage curves and impedance spectroscopy. The best achievable inverted solar cell efficiency, open circuit voltage and current density short circuit were 1.475%, 0.463 V and 10.125mA/cm2 respectively for ITO/ZnO/P3HT: C60 /RuO2/PEDOT:PSS/Au cell structure, this obtained efficiency is 8 times the efficiency of the cell without using the new RuO2 buffer layer.

55

Poster Session

Poster 13

Author(s): Leow Wan Ru

Affiliation(s): Nanyang Technological University, School of Materials Science and Engineering


Title: Al2O3 Surface Complexation for Photocatalytic Organic Transformations

Abstract:The use of sunlight to drive organic reactions constitutes a green and sustainable strategy for organic synthesis. Herein, we discovered that the earth-abundant and commercially-available aluminum oxide (Al2O3), though paradigmatically known to be an insulator, could elicit an immense increase in the selective photo-oxidation of different benzyl alcohols in the presence of different dyes and O2. This unique phenomenon is based on the surface complexation of benzyl alcohol (BnOH) with the Brønsted base sites on Al2O3, which reduces its oxidation potential and causes an upshift in its HOMO for electron abstraction by the dye. The surface complexation of O2 with Al2O3 also activates the adsorbed O2 for receiving electrons from the photoexcited dyes. This discovery brings forth the potential of utilizing surface complexation mechanisms between the reactants and earth abundant materials to effectively achieve a wider range of photoredox reactions.

56

Poster Session

Poster 14

Author(s): Cheng Zhang, Thanh Nhut Do and Howe-Siang Tan*

Affiliation(s):


Title: Understanding the Two-dimensional Electronic Spectra Peak Shapes of CdSe Quantum Dots

Abstract:Semiconductor nanomaterials are considered as a promising focus to both fundamental and applied research and development nowadays due to its unique physical and chemical properties. We perform Two-dimensional Electronic Spectroscopy (2DES) using a pump-probe geometry with a programmable acousto-optic pulse shaper and 1 by 4 phase-cycling scheme [1,2] to retrieve clean purely 2D spectra of CdSe nanocrystal quantum dots (QDs). We seek to understand the peak shapes of various excitonic and biexcitonic transitions of the QDs. We observe and propose a Zero Line Slope (the line that 2D peaks transits from positive to negative) analysis to study the homogeneous and inhomogeneous and spectral diffusion contributions [3] to the 2D peak shape of QDs.

References:[1] H. S. Tan, J. Chem. Phys. 129, 124501 (2008).

[2] Z. Zhang, K. L. Wells, E. W. J. Hyland and H. S. Tan, Chem. Phys. Lett. 550, 159 (2012).

[3] M. Wolf and J. Berezovsky, Appl. Phys. Lett. 105, 143105 (2014).

57

Poster Session

Poster 15

Author(s): Nitin Loganathan, Yi-Chin Candace Tsai and Oliver Mueller-Cajar

Affiliation(s): School of Biological Sciences, Nanyang Technological University


Title: A biochemical dissection of the red algal Rubisco Activase

Abstract:The key photosynthetic CO2-fixing enzyme rubisco is prone to form stably inhibited complexes with its substrate ribulose 1,5-bisphosphate and other sugar phosphate inhibitors, such as catalytic misfire products. In plants the molecular chaperone rubisco activase is essential to continually service inhibited rubisco active sites to maintain photosynthetic CO2 fixation. Recently it was shown that the red-type rubisco of α-proteobacteria is activated by a convergently evolved red-type rubisco activase CbbX. All red lineage phytoplankton appear to encode two CbbX isoforms, one in the nuclear genome and one in the plastid genome. We have performed a detailed biochemical characterization of the two CbbX isoforms encoded by the red algae Cyanidioschyzon merolae. We find the purified isoforms are inactive in isolation, but when mixed form functional hetero-hexamers of 1:1 stoichiometry. Extensive site-directed mutagenesis was used to perform a detailed dissection of isoform function. In summary the nuclear isoform appears dominant, and mutation of ATPase or activation relevant residues generally eliminates function of the hetero-oligomer. In contrast the plastid-encoded isoform is more tolerant of mutagenesis, consistent with a more structural role. We anticipate our findings to generally apply to the CbbX proteins of eukaryotic red-lineage phytoplankton.

58

Poster Session

Poster 16

Author(s): Muhammad Faisal bin Khyasudeen, Zhentang Liu, Parveen Akhtar, Petar h. Lambrev, Howe-Siang Tan

Affiliation(s): Nanyang Technological University


Title: Ultrafast processes in Photosystem I using pump-probe and two-dimensional electronic spectroscopy

Abstract:Photosystem I (PSI) in higher plants comprises a core complex and four peripheral antenna subunits (LHCI). The PSI core pigments establish a highly optimized energy-transfer network delivering excitation energy to the reaction center on a subpicosecond time scale, whereas the relatively weaker coupling of the LHCI antenna and the presence of low-energy “red” chlorophylls poses a certain kinetic limitation to the overall photochemical process. Despite this, the photochemical quantum yield of the PSI-LHCI supercomplex is near unity. The ultrafast processes of energy equilibration and trapping have been extensively studied in PSI from cyanobacteria and green algae, which have smaller pools of low-energy chlorophylls. Here we employed femtosecond transient absorption and two-dimensional electronic spectroscopy (2DES) PSI-LHCI and PSI core complexes from pea, to study the ultrafast kinetics of energy transfer, with emphasize on distinguishing excitation energy equilibration with “red” chlorophylls in the core complex and in LHCI. The transient absorption results are compared with literature data on PSI from cyanobacteria and green algae. Despite the remarkable overall similarity in the highly conserved PSI from different evolutionary lineages, our results reveal characteristic traits of the higher-plant PSI-LHCI. Further details on the ultrafast dynamics of exciton relaxation in the core and peripheral antenna are revealed by room-temperature 2DES.

59

Poster Session

Poster 17

Author(s): Parveen Akhtar, Mónika Lingvay, Győző Garab, Petar H. Lambrev

Affiliation(s): Hungarian Academy of Sciences, Biological Research Centre, Szeged, Hungary


Title: Reconstituted membranes of Photosystem I and LHCII show efficient energetic connectivity and resistance to photodamage

Abstract:Light-harvesting complex II (LHCII), the major peripheral antenna of Photosystem II in plants, in addition to its primary light-harvesting function plays a major role in regulating and balancing the flow of excitation energy in thylakoid membranes. In part, these include interaction of LHCII with PSI enhancing the latter’s absorption cross-section – for example in the well-known state 1 – state 2 transitions or as a long-term acclimation to high light. In this work we examined the capability of LHCII to deliver excitations to PSI and whether PSI could protect LHCII from photodamage in vitro by way of excitation trapping. Reconstituted membranes with plant thylakoid membrane lipids and LHCII:PSI at different stoichiometric ratios were studied by steady-state absorption, CD and fluorescence spectroscopy, as well as time-resolved fluorescence. Different pools of LHCII were found to transfer energy to PSI on time scales from less than 10 ps to hundreds of ps, contributing significantly to the effective antenna size of PSI. The overall efficiency of transferring excitations from LHCII was up to 70%. As a result of the energetic connectivity, the average chlorophyll excited-state lifetime was shorter thus limiting the possibility to generate damaging reactive oxygen species. This was manifested by higher photostability of PSI-LHCII membranes compared to LHCII-only membranes under continuous irradiation.

60

Poster Session

Poster 18

Author(s): Petar H. Lambrev, Parveen Akhtar, Miriam M. Enriquez, Cheng Zhang, Győző Garab, and Howe-Siang Tan

Affiliation(s): Nanyang Technological University Hungarian Academy of Sciences, Biological Research Centre


Title: Exciton Relaxation in Light-Harvesting Complex II Probed by 2D Electronic Spectroscopy

Abstract:Light-harvesting complex II (LHCII) is functionally flexible and mobile component of the plant photosynthetic membrane, able to alter the granal structure and the energy flow in response to the environmental conditions. Isolated LHCII show different spectroscopic signatures in detergent-solubilized or aggregated state. We examined the exciton relaxation and equilibration dynamics in the Chl a domain in isolated LHCII trimers, aggregates, and reconstituted LHCII:lipid membranes by using two-dimensional electronic spectroscopy (2DES). Correlating the frequencies of coupled exciton states, ultrafast transient 2DES is a powerful technique to resolve the excited-state dynamics in complex multichromophore systems such as LHCII. We were able to resolve different pathways of exciton relaxation occurring on time scales from hundreds of femtoseconds to several picoseconds. The relaxation of specific intermediate-energy Chl a exciton states was accelerated in quenched LHCII aggregates compared to trimers or reconstituted membranes. The results shed new light on the energy transfer and excitation quenching dynamics relevant to the processes of light harvesting and photoprotection in natural photosynthesis.

61

Poster Session

Poster 19

Author(s): Lin Qin, S Thivyaa Tharrshini, Jie He

Affiliation(s): Natural Sciences and Sciences Education Academic Group, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616


Title: Photosynthetic responses of green leaves and green pseudobulbs of CAM orchid Guarianthe skinneri to rewatering following mild and severe drought stress

Abstract:CAM orchid, Guarianthe skinneri plants were first subjected to mild (MDS) and severe drought stress (SDS), which were defined by the reductions of chlorophyll fluorescence Fv/Fm ratio of green leaves (GL) from about 0.800 to about 0.700 and 0.500, respectively. Compared to well-watered (WW) plants, there were no significant decreases in GL water content after MDS and SDS. Water content of green pseudobulbs (GPSB) was, however, lower in MDS and SDS plants. After rewatering (RW), predawn and midday Fv/Fm ratios of all plants recovered by 90% on the first day. Photochemical quenching (qP) and electron transport rate (ETR) were lower in GL and GPSB of DS plants. GL protected its photosynthesis through higher non-photochemical quenching, qN but this was not found in GPSB. After RW, qP of GL had recovered for MDS and SDS plants. However, qP of GPSB for SDS plants was unable to recover. Upon RW, recoveries of CAM acidity were observed in GL of MDS and SDS plants and GPSB of MDS plants but this was not seen in GPSB of SDS plants. All findings support that water transport from GPSB into GL had occurred to maintain photosynthesis of GL during DS and RW periods.

62

Poster Session

Poster 20

Author(s): Shawn Tay1, Jie He1*, & Tim Wing Yam2

Affiliation(s): 1Natural Sciences and Science Education Academic Group, National Institute of Education, Nanyang Technological University, Singapore 2Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Singapore


Title: Light use efficiency under drought stress in native tropical orchids Coelogyne mayeriana and Phalaenopsis cornu-cervi

Abstract:In some epiphytic orchids, Crassulacean acid metabolism (CAM) is a significant water conservation strategy that enables closure of stomata in the day to reduce excessive water loss. However, it is not well understood in the context Singapore’s native orchid species whether CAM presents an advantage over C3 in light use efficiency under drought stress. In this study, two native orchid species, Coelogyne mayeriana (C3) and Phalaenopsis cornu-cervi (CAM) were exposed to deliberate drought treatment in the greenhouse. Their water status was measured by relative water content and their light use efficiency measured by midday chlorophyll Fv/Fm ratio. Under moderate light conditions of photosynthetic photon flux density around 300 µmol m-2 s-1 and drought stress, RWC decreased by 33.8% in C. mayeriana and 11.0% in P. cornu-cervi. Fv/Fm ratio decreased to 0.469 under drought stress compared with 0.783 under well-watered conditions. The results suggest that water is significant in mitigating light stress even under moderate light conditions. Between the two orchid species, CAM provides an advantage over C3 in light use efficiency under drought stress. This is important for survival of native orchid species under natural conditions.

63

Poster Session

Poster 21

Author(s): Cheng Hsiang Lai, Jie He



Title: Photosynthetic responses to heat stress in root-zones of temperate crops aeroponically grown in the tropics

Abstract:In face of climate changes, understanding thermotolerance conferment and cultivation of heat tolerant food crop is of particular urgency. A total of ten commercial cultivars, recombinant in-bred lines (RILs) and their parental lines of Lactuca sativa were examined in this study for their response in long term exposure to root zone temperatures (RZTs) of 25, 28, 32 and 36˚C while their shoots were exposed to fluctuating ambient temperature from 25 to 38˚C. Physiological performance of these vegetables at each RZT was evaluated by examining their integral photosynthetic efficiency including productivity, oxygen evolution, chlorophyll fluorescence, photosynthetic pigment content and root development. Cellular responses such as total reduced N status and total soluble protein levels and biochemical responses like Rubisco content and heat shock protein synthesis were also investigated. Of the ten vegetables explored, lettuce RIL 142, cv. Arugula (E. sativa), and wild type lettuce (L. serriola) were thermotolerant while L. sativa (cv. Nanda), lettuce RILs 192, 195 and red lettuce (L. sativa), on the other hand, thermosensitive. These species will be further explored with respect to conferment of thermotolerance and “hardening” potentials to boost thermotolerance.

64

Poster Session

Poster 22

Author(s): Jie He, Xin Er See, Lin Qin, Tsui Wei Choong,



Title: Photosynthesis and nutritional quality of salad rocket vegetable grown in the tropical greenhouse with manipulation of root-zone temperature

Abstract:In this research, we studied the impact of various rootzone temperatures (RZTs) on the photosynthesis and nutritional quality of a Mediterranean rocket salad, Eruca sativa. Aerial parts of plants were aeroponically grown under tropical fluctuating ambient temperatures with their roots exposed to four different RZTs: constant cool (C-RZT) of 20oC-, 25°C-, 30°C-, and fluctuating ambient (A-RZT) from 25oC to 38oC. On sunny days, high midday photosynthetic photon flux density induced dynamic photoinhibition, indicated by < 0.8 chlorophyll fluorescence Fv/Fm ratios. However, RZ cooling alleviated this condition. There were no significant differences in photosynthetic CO2 assimilation rate, electron transport rate, photochemical and non-photochemical quenching among plants grown under all three C-RZTs though these parameters were significantly higher than those of A-RZT plants. Highest productivity was found in E. sativa plants grown at 20°C-RZT. It had well-developed roots, high mineral and low total phenolic content. In contrast, A-RZT plants had lowest productivity, poorly developed roots, low mineral and high phenolic content. These results suggest that RZT affects photosynthetic utilization of radiant energy of temperate E. sativa grown under natural tropical conditions. Thus, root cooling could be introduced during cultivation, in Singapore, to obtain higher productivity and dietary mineral content in E. sativa

65

Poster Session

Poster 23

Author(s): Yi-Chin Candace Tsai

Affiliation(s): Postdoctoral Fellow, School of Biological Science, NTU


Title: Identification and characterization of the Rubisco activases of chemoautotrophic bacteria

Abstract:The key photosynthetic CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) is renowned for its slow kinetics and poor substrate specificity, making it a prominent target for crop improvement efforts. In addition it is prone to dead-end inhibition by sugar phosphates, including its substrate ribulose-1,5-bisphosphate (RuBP). This led to the convergent evolution of at least two classes of rubisco activases, the AAA+ proteins (ATPases associated with various cellular activities) Rca and CbbX, which catalyze the ATP-dependent release of inhibitors from green- and red-type form I rubisco respectively. Here we characterize a third class of rubisco activase in the chemolithoautotroph Acidithiobacillus ferrooxidans. We show that two sets of isoforms of the CbbQ and CbbO proteins, which are encoded downstream of form I and form II rubisco genes respectively, form hetero-oligomeric complexes that can remove both RuBP and the carboxylation transition state analogue carboxyarabinitol-1,5-bisphosphate (CABP) from the enzymes they are genetically linked to. The MoxR family AAA+ protein CbbQ forms a ring-shaped hexameric particle and functions as the motor of the activase. CbbQ hexamers associate with one CbbO subunit that functions as essential substrate adaptor. The mechanism of activation between isoforms is conserved, with the CbbO protein binding rubisco at a conserved acidic surface residue via a C-terminal von Willebrand Factor A (VWA) domain and manipulation of the rubisco large subunit C-terminus being essential for function.

66

Poster Session

Poster 24

Author(s): Evgeni B. Starikov

Affiliation(s): KIT, Karlsruhe, Germany; Chalmers, Gothenburg, Sweden.


Title: Foundations of Thermodynamics

Abstract:

• HowmanyBasicLawshasthermodynamics?Only one: The Energy Conservation and Transformation Law. All other laws and rules in the field are consequences of these both.

• ThermodynamicsandTime–aprofoundconceptualincompatibility?The both are perfectly compatible. The Time Notion ought to be used both implicitly and explicitly for solving thermodynamic problems.

• Whatistheactualphysicalsenseoftheentropynotion?The therrmodynamic notion of entropy means nothing more and nothing less than just ubiquitous obstacles to the progress achieved by the relevant driving forces.

• Whatcouldbethepropermathematicaltoolsforthetruenon-equilibriumthermodynamics? A differential game theory.

Poster Session

Poster 25

Author(s): Tsui Wei CHOONG1, Jie HE1, Sing Kong LEE1, Ian DODD2

Affiliation(s): 1Natural Sciences and Sciences Education Academic Group National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616 2Lancaster Environment Centre, Lancaster University, Lancaster, United Kingdom


Title: Influence of rootzone ethylene accumulation under different rootzone temperatures on light use efficiency and growth of Lactuca in a tropical greenhouse

Abstract:Little is known about the effect of rootzone (RZ) ethylene accumulation, under different rootzone temperatures (RZT), on a plant’s photosynthetic light use efficiency and productivity. In this study, a recombinant inbred line (RIL) of lettuce and its parental lines (L. serriola x L. sativa ‘Salinas’) were aeroponically grown in a tropical greenhouse under 24°C cool- (C) or 32°C warm-RZT (W-RZT). Their roots were misted with nutrient solution, for 1 min, at intervals of 5 min (C5, W5) or 10 min (C10, W10). Accumulated RZ ethylene concentrations were measured and higher concentrations were found in C10 and W10, than C5 and W5, respectively. In the RIL, higher concentrations corresponded with lower photochemical quenching, qP and electron transport rate, ETR whilst contrasting with high non-photochemical quenching, NPQ. With higher RZ ethylene accumulated at W-RZT, all plants showed lower shoot and root fresh weights, and specific leaf area (SLA). In all, the high RZ ethylene accumulated corresponded with high NPQ and carotenoid (data not shown) content, as well as low shoot and root fresh weights and smaller SLA. As such, further research on increasing RZ ethylene concentrations could be carried out to more clearly study its influence on light use efficiency.

Institute of Advanced StudiesNanyang Executive Centre

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Singapore 639673Tel: (65) 6790 6491, 6592 1880

Fax: (65) 6794 4941Website: http://www.ntu.edu.sg/ias

Documents

th International Workshop on Solar Energy for … International Workshop on Solar Energy for Sustainability “Photosynthesis and Bioenergetics” 21 to 24 March 2016 Nanyang Executive