A combination of structure with biological function: A signal transduction note

7/28/2019 A combination of structure with biological function: A signal transduction note

1/35

Israr Khan

School of Biological Sciences,

University of the Punjab, Punjab,P.O 54590, Lahore, Paksitan

03349301550


2/35


3/35

Israr Khan

M. Waheed Akhtar

Javed Iqbal

A.R. Shakoori

Aftab Ahmed Chatta

Sajjad Ahmad Sajjal

Nasir Ali Khan

Raza Ashraf

A Shortnote On Signal

Transduction

Scribd


4/35


5/35

5

Israr khan

is the Editor of the S.A.T journal (applied) and the founder of thesame.http://pastehtml.com/view/csk735k7np.html

M. Waheed Akhtar

is the Director of the School of biological Sciences, University ofthe Punjab, Pakistan and the founder of PSBMB and PJBMB.http://psbmb.org.pk/ andhttp://psbmb.org.pk/journal.htm

A.R. Shakoori

is the Director of the School of biological Sciences, University ofthe Punjab, Pakistan and the founder of international/pakistan

journal of zoology and society Pakistan.http://zsp.com.pk/pjz.html

Disclaimer

Biotechnology is the science and art of using biological organisms and materials forthe welfare of human beings and is one of the rapidly advancing and dominatingfield of biological science . therefore we, the authors have taken due care to providetruth in abstract form to the readers. To err is human and as such this work too

consists some errors which are solely mine alone. And therefore for compensationthe book is entitled as prevention and not treatment despite the need to do so, andrecent knowledge along webadresses of all authors incase of emergency can becontacted. The data hereby is a public property and works under the creativecommons 3.0 attribution non for business purpose licence. Thereby applying anyworkable techniques is the sole responsibility of the working group on their own.

This work is protected by copyright both as a whole and in part. 2014 by ISBN: xxxxxx-xx-x. (will be provided by Flying Publisher)


6/35

6 |

Preface

The work consists of workable and reproducible protocols inMolecular biology and biochemistry that give rise to biotechnologyand still used in recenty fields of medical science and neurosurgery.

The writing is therefore more of a practice book than medicinealone and gives some futuristic view of technology merging theinformation technology to sort out a fast solution to the problems

today and in future. Thereby the medium of the manuscript is keptenglish in order to spread the message of peace around the world.

Any suggestions willbe welcome in this regard for the furtherimprovement of the content.

Israr Khan

June 2013


7/35

| 7

Contributing Authors

Israr Khan

PhD ScholarSchool of biological Sciences,University of the Punjab,54590, Lahore, [email protected]

Prof. Dr. M. Waheed Akhtar

School of biological sciencesUniversity of the PunjabNew Campus (QEA)54590, [email protected]

Prof. Dr. A.R. Shakoori

School of biological sciencesUniversity of the PunjabNew Campus (QEA)54590, [email protected]

Raza Ashraf

Department of botanyUniversity of the PunjabNew campus54590, [email protected]

Nasir Ali Khan Aftab Ahmed Chatta

Project coordinator Animal cell culture,Disease early warning system, SBS, PU, Lahore, Pakistan.DEWS, [email protected]

Sajjad Ahmad SajjalBiological Systems engineering,Virginia technical, Viginia, USA.


8/35

8 |

Abbreviations

AHA: autoimmune-haemolytic

anaemiaAlb-IFN: albumin interferonAHA: autoimmune-

haemolyticanaemiaAlb-IFN:

albumin interferonAHA: autoimmune-haemolytic

anaemiaAlb-IFN: albumin interferonAHA: autoimmune-

haemolyticanaemiaAlb-IFN: albumin interferonAHA: autoimmune-

haemolyticanaemiaAlb-IFN: albumin interferon


9/35

| 9

Table of Contents

1. Definition of signal transduction ............................................ 11Introduction to signal transduction ...................................... 12

2. The components of cellular communication ............................ 13What type of signals do cells send ....................................... 13Communication is funneled through receptors ..............Error!

Bookmark not defined.14Changing a signal into behaviour ........................................ 15

3. Receptors ............................................................................... 19Peripheral protein membrane receptors................................ 17Transmembrane receptors ................................................... 17

Types of membrane receptors ......................................... 18

Types of transmembrane receptors ...................................... 194. Intracellular receptors ............................................................ 20

Second messengers ............................................................. 20Major pathways .................................................................. 20About acetylecholine and its receptors ................................ 21

12. References ............................................................................. 34


10/35

1.Figure 1.Signal Transduction

Israr Khan


11/35

A Shortnote on Signal transduction | 11

The impotance of being part of the chain of events is like aball of a game thrown at something lets say A that connects objectB and then C, D ,E , F and so on untill the the final object of thegame lets say Z reaches , but this game has a function in biologyand after Z their occurs a sequence of changes that can bememorized and repeated the same way or habituated to bring

changes or signals to cells.

1. Definition of signal transductionThe intercellualr/intracellular transfer of information that may be

biological activation or inhibition, through a signal pathway whichinvolves oredered sequences of biochemical reactions inside the cellwith an activation or inhibition signal from a biologically active

molecule such as hormone , neurotransmitter. And is mediatedthrough the coupling of a receptor/enzyme to a second meseengersystem or to an an ion channel resulting in a signal transduction

pathway or cascade thus involved in controlling growth,development, metabolism and behaviour of an organism thus anydefects in these pathways can lead to specific disfunctions ordiseases. Normal end results may be

Gene regulation Cell proliferation and Apoptosis etc


12/35

12 | A Shortnote on Signal transduction

Introduction to signal transduction

A signal interacts witha receptor on the cell surface, causing achange ina second messenger or ion channel thereby changing thecells function for instance a hormone or merotramsnitter causing achange in calcium channel thereby deviding the cell. In the wholeanimal, signal transduction controls growth, development,metabolism and behavior. In individual cells, signal transduction iscrucial for decisions about essential processes such as cell division

and metabolic control. Signal transduction processes are usuallyrapid, lasting on the order of milliseconds in the case of ion flux, orminutes for the activation of protein- and lipid-mediated kinasecascades, but some can take hours, and even days to complete.

History and background

It dates backto 1972 when first paper was published using the termsignal transduction also known as sensory transduction later on.

The total number of scientific papers related to signaltransduction published since 1st Jan 1977 up to the 31st December

2007 was 48,377 of which only 11,211 are reviews.

Figure 3: Occurrence of the term signal transduction(MEDLINE database.)


13/35


2.The componets of communicationIsrar khan

Figure 4. Types of signals.

The three basic components involved in cell signaling are;

1. What type of signal do cells send? Signalling molecules thattransmit the signal are a variety of organic and inorganic chemicalmolecules that surround the cell. These signaling molecules have

been functionally classified as:

hormones (e.g., melatonin), growth factors (e.g. epidermal growth factor), extra-cellular matrix components (e.g., fibronectin), cytokines (e.g., interferon-gamma), chemokines (e.g., RANTES), neurotransmitters (e.g., acetylcholine), and Neurotrophins (e.g., nerve growth factor).


14/35


2. Communication is funneled through Receptors the

signal binds a specific receptor that recognize the signal, and thesereceptors are present on the surface of the cell acoording to anumber of specific needs. Like a key fitting into a lock. Thereby thecell is considered to have received the signal and transducer the cellinto changes or behavior, thereby the cells can do a number ofactions or reactions termed as behavior.


15/35


3. Changing a signal (intracellular or outside the cell) intoBehaviour, involves a sequential cascade from signals to behabiourvia receptor/s protein thus using the cell machinery for instance the

bahaviour of gene activation (enzymes and transcription factors),metabolic alterations, cell proliferation, cell apoptosis andstimulation or suppression of locomotion. Transcription factor canyet activate some more genes in turn therefore an initial signal cangive rise to varied physiological events. For instance theuptake ofglucose from blood stream by insulin, migration of neutrophils to

the site of infection attracted to bacterial products through a certaingenetic program. Similarly neurotransmitters bind to an ion channelprotein flowing ions rapidly through plasma membrane likeelectrochemical impulses.


16/35


3.ReceptorsA receptor is a protein molecule, embedded in either the

plasma membrane or cytoplasm of a cell, to which a mobilesignaling (or "signal") molecule may attach. A molecule which

binds to a receptor is called a "ligand," and may be a peptide (suchas a neurotransmitter), a hormone, a pharmaceutical drug, or atoxin, and when such binding occurs, the receptor undergoes a

conformational change which ordinarily initiates a cellularresponse. However, some ligands merely block receptors withoutinducing any response (e.g. antagonists). Ligand-induced changesin receptors result in physiological changes which constitute the

biological activity of the ligands.

Types of receptors:

Depending on their functions and ligands, several types of receptorsmay be identified:

(A) Some receptor proteins are peripheral membraneproteins.

(B) Many hormone and neurotransmitter receptors aretransmembrane proteins: transmembrane receptors (1. Ion

channel linked receptors, 2. Enzyme linked receptors and3. G-protein linked receptors) are embedded in thephospholipid bilayer of cell membranes, that allow theactivation of signal transduction pathways in response tothe activation by the binding molecule, or ligand.

o (B1) Metabotropic receptors are coupled to Gproteins and affect the cell indirectly throughenzymes which control ion channels.

o (B2) Ionotropic receptors (also known as ligand-gated ion channels) contain a central pore whichopens in response to the binding of ligand.

(C). Another major class of receptors are intracellularproteins such as those for steroid and intracrine peptidehormone receptors. These receptors often can enter the cell


17/35


nucleus and modulate gene expression in response to theactivation by the ligand.

A. Peripheral membrane protein receptors

These receptors are relatively rare compared to the muchmore common types of receptors that cross the cell membrane. Anexample of a receptor that is a peripheral membrane protein is theelastin receptor.

B. Transmembrane receptors

Membrane orTransmembrane receptors are specializedintegral membrane proteins consists of an extracellula, intracellularand a transmembrane domain, that takes part in communication

between the the cell and the outside world. Extracellularsignaling

molecules (usually hormones, neurotransmitters, cytokines, growthfactors or cell recognition molecules) attach to the receptor,triggering changes in the function of the cell. This process is calledsignal transduction: The binding initiates a chemical change on theintracellularside of the membrane. In this way the receptors play aunique and important role in cellular communications and signaltransduction.


18/35


Types of membrane receptors membrane receptors are mainlydivided into 3 classes based on structural and functional similarities:The ion channel-linked receptor; The enzyme-linked receptorand G

protein-coupled receptor.

1. Ion channel-linked receptors are ion-channels (includingcation-channels and anion-channels) themselves and constitute a

large family of multipass transmembrane proteins. They areinvolved in rapid signaling events most generally found inelectrically excitable cells such as neurons and are also calledligand-gated ion channels. Opening and closing of Ion channels arecontrolled by neurotransmitters. For instance Acetylcholinereceptor is a kind of cation-channel linked receptor.

2. Enzyme-linked receptors are either enzymes themselves, orare directly associated with the enzymes that they activate. Theseare usually single-pass transmembrane receptors, with theenzymatic portion of the receptor being intracellular. The majorityof enzyme-linked receptors are protein kinases, or associate with

protein kinases. There are 6 known types ELRs.

3. G protein-coupled receptors

G protein linked receptors are integral membrane proteinsthat possess seven membrane-spanning domains or transmembranehelices. These receptors activate a G protein ligand binding. G-

protein is a trimeric protein. The 3 subunits are called , and .The subunit can bind with guanosine diphosphate, comprise a

large protein family transmembrane receptors that possess sevenmembrane-spanning domains.


19/35


Types of transmembrane receptors

Nasir Ali Khan, DEWS.These are two main classes of trasmembrane receptors;Ionotrophic and Metabotropic receptors

The Function of metabotropic receptors haveneurotransmitters as ligands. When a ligand, also called the primarymessenger, binds to the receptor, or the transducer, the latteractivates a primary effector, which can go on to activate secondarymessengers or have other effects., involved in mechanisms thatrequire quick responses (Kandel et al., 2000, p. 240). However,metabotropic receptors also remain open from seconds to minutes(Kandel et al., 2000, p. 250-251). Thus they have a much longer-lasting effect than ionotropic receptors, which open quickly butonly remain open for a few milliseconds (Austin, 2004). They can

make a membrane more excitable by closing K

+

channels, retainingpositive charge within the cell and thus reducing the amount ofcurrent necessary to cause an action potential (Kandel et al., 2000,

p. 242-243). Metabotropic receptors on the presynaptic membranecan inhibit or, more rarely, facilitate neurotransmitter release fromthe presynaptic neuron (Schmitz et al., 2001).

Ionotropic receptors (ligand gated ion receptors)

Ligand-gated ion channels (LGICs), also referred to asionotropic receptors or channel-linked receptors and a group oftransmembrane ion channels that are opened or closed in responseto the binding of a chemical messenger (i.e., a ligand), such as aneurotransmitter. Ionotropic receptors are heteromeric orhomomeric oligomers. They are receptors that respond toextracellular ligands and receptors that respond to intracellular

ligands. While ionotropic channels have an effect only in theimmediate region of the receptor.


20/35


4.Intracellular receptors These are located inside the cell rather than membrane. These are soluble in the cytoplasm. For instance IP3receptor in EPR and nuclear receptors. The nuclear receptors further activate hormone responsive

elements (HREs) at DNA level. The nucleic receptors all have a similar, modular structure:

N-AAAABBBBCCCCDDDDEEEEFFFF-C. whereCCCC is the DNA-binding domain that contains zincfingers, and EEEE the ligand-binding domain. The latter isalso responsible for dimerization of most nuclearicreceptors prior to DNA binding. e.g. Steroid receptors area subclass of nuclear receptors, located primarily withinthe cytosol. In the absence of steroid hormone, the

receptors have chaperone proteins as well and clingtogether in a complex called an aporeceptor complex.RXR- and orphan-receptors are are located in thenucleus and are notaccompanied by chaperone proteins.

Certain intracellular receptors of the immune system areexamples of cytoplasmic receptors. Recently-identified

NOD like receptors (NLRs) reside in the cytoplasm of

specific eukaryotic cells and interact with particularligands, such as microbial molecules, using a leucine-richrepeat (LRR) motif that is similar to the ligand-bindingmotif of the extracellular receptors known as TLRs.

Second messengers

Intracellualr signal transduction is largely carried out by second

messeamger moleculaes these include calcium, liphopihilic andnitric (NO) messengers.

Major Pathways

The major signalling pathways include the cAMP dependentpathway, MAP/ERK pathway and IP3/DAG pathway.


21/35


Acetylcholine and its receptors

The nervous system communicates with the body bysending electrical impulses from the central nervous system (CNS)through long nerves cells (neurons) to the peripheral nervoussystem (PNS), muscles and glands. When an electrical nerveimpulse reaches a junction with another nerve cell (synapse), or

with a muscle cell (neuromuscular junction), it must transmit itssignal by chemical means. The influx of ions at a synaptic orneuromuscular junction stimulates the release of vesicles containingneurotransmitters (e.g.; acetylcholine), which diffuse across thegap and bind to receptors on the adjoining nerve or muscle cell,thereby continuing the response.

Neurotransmitters/ Chemical SignalsThere are various types of neurotransmitters that elicit

different, and sometime opposing, types of responses. One of thefirst neurotransmitters to be discovered was acetylcholine(Changeux et al, 1970), which is produced by the enzyme cholineacetyltransferase, using acetyl coenzyme A (acetyl CoA) anddietary choline as substrates. Acetylcholine release can be either

excitatory (promoting a signal), or inhibitory depending upon thetype of receptor on the adjoining cell. Once acetylcholine hasactivated its receptor to transmit its signal, it needs to be brokendown to prepare the synapse for the arrival of the next signal; this isaccomplished by the enzyme acetylcholinesterase, which removesacetylcholine from the synapse by breaking it down into inactivefragments. Nerve gases such as sarin that are used in warfare, as

well as organophosphate insecticides such as parathion, achievetheir effects through the inhibition of acetylcholinesterase, therebyallowing acetylcholine to remain active and in contact with itsreceptor. Antidotes such as atropine are used to block acetylcholinereceptors, thereby nullifying the effects of excessive acetylcholine.


22/35


How does acetylcholine work?

By binding to a receptor on an adjoining cell, acetylcholinecan cause the activation of the receptor, which can then havedifferent downstream effects, depending upon whichacetylcholine receptor is activated. These effects lead to acascade of events that transmit the signal inside the cell,resulting in the continuation of a nerve impulse, the movementof muscle, or many other responses in a variety of different

tissues. For example, the sight, smell and taste of food cancause the vagus nerve to release acetylcholine, which binds toreceptors on parietal cells, causing an influx of calcium ionsthat activate intracellular phosphokinase enzymes; this in turnresults in the activation of a proton pump to expel hydrogenions, which can then combine with chloride ions to form thehydrochloric acid that is required for the digestion of food in

the stomach.Acetylcholine receptors:

An acetylcholine receptor (abbreviated AChR) is anintegral membrane protein that responds to the binding ofneurotransmitter acetylcholine and consists of ion channels or G

protein coupled located principally over the peaks of the

postsynaptic folds, where they are present at high density andconsist of five subunits.

Types of Acetylcholine Receptors:

There are two types of acetylcholine receptors (AChR) thatbind acetylcholine and transmit its signal. Although all

acetylcholine receptors, by definition, respond to acetylcholine,they respond to other molecules as well. Muscarinic AChRs andnicotinic AChRs, which are named after the agonists muscarineand nicotine, respectively. These receptors are functionallydifferent, the muscarinic type being G-protein coupled receptors(GPCRs) that mediate a slow metabolic response via secondmessenger cascades, while the nicotinic type are ligand-gated ion


23/35


channels that mediate a fast synaptic transmission of theneurotransmitter.

Muscarinic Cholinergic Receptors (mAChR/metabotropic

acetylcholine receptors)

Muscarinicreceptors are

characterised throughtheir interaction withmuscarine, a water-soluble toxin derivedfrom the mushroom

Amanita muscaria thatcauses substantial

activation of theperipheral sympatheticnervous system throughits binding tomuscarinic AChRs,resulting in convulsionsand even death. Themuscarinic AChRs

occur primarily in the CNS, and are part of a large family of G-protein-coupled receptors (G proteins), which use anintracellular secondary messenger system involving an increase ofintracellular calcium to transmit signals inside cells. Binding ofacetylcholine to a muscarinic AChR causes a conformationalchange in the receptor that is responsible for its association with andactivation of an intracellular G protein, the latter converting GTP toGDP in order to become activated and dissociate from the receptor.The activated G protein can then act as an enzyme to catalysedownstream intracellular events.

Muscarinic receptors are involved in a large number ofphysiological functions including heart rate and force, contractionof smooth muscles and the release of neurotransmitters. There are

Amanita muscaria


24/35


five subtypes of muscarinic AChRs based on pharmacological

activity: M1-M5. All five are found in the CNS, while M1-M4 arealso found in various tissues: M1 AChRs are common in secretoryglands; M2 AChRs are found in cardiac tissue; M3 AChRs arefound in smooth muscles and in secretion glands. M1, M3 and M5receptors cause the activation of phospholipase C, generating twosecondary messengers (IP3 and DAG) eventually leading to anintracellular increase of calcium, while M2 and M4 inhibitadenylate cyclase, thereby decreasing the production of the secondmessenger cAMP. The activation of the M2 receptor in the heart isimportant for closing calcium channels in order to reduce the forceand rate of contraction.

Nicotinic cholinergic receptors (nAChR/ionotropic acetylcholine

receptors)

Nicotinic receptors are characterised through theirinteraction with nicotine in tobacco. The nicotinic AChRs areligand-gated ion channels that form pores in cells plasmamembranes, mediating fast signal transmission at synapses.

Nicotinic AChRs are involved in a wide range of physiologicalprocesses, and can be either neuronal or muscle-type. Muscle-typenicotinic AChRs are localised at neuromuscular junctions, where anelectrical impulse from a neuron to a muscle cell signals contractionand is responsible for muscle tone; as such, these receptors aretargets for muscle relaxants. The many types of neuronal nicotinicAChRs are located at synapses between neurons, such as in theCNS where they are involved in cognitive function, learning andmemory, arousal, reward, motor control and analgesia.

The binding of acetylcholine to nicotinic AChRs bringsabout their activation. When two molecules of acetylcholine bind a

nicotinic AchR, a conformational change occurs in the receptor,resulting in the formation of an ion pore. At the neuromuscular

junction, the opening of a pore produces a rapid increase in thecellular permeability of sodium and calcium ions, resulting in thedepolarisation and excitation of the muscle cell, thereby producinga muscular contraction.


25/35


The activation of neuronal nicotinic AChRs also causes themovement of cations

through the opening of an ion channel, withthe influx of calcium ions affecting the release of neurotransmitters.Nicotinic AChRs on a postganglionic neuron are responsible for theinitial fast depolarisation of that neuron. However, the subsequenthyperpolarisation and slow depolarisation, which represent therecovery of the postganglionic neuron from stimulation, aremediated by muscarinic AChR types M2 and M1, respectively. The

binding of nicotine can activate nicotinic AChRs, modifying theneurons in two ways: the depolarisation of the membrane throughthe movement of cations results in an excitation of the neuron,while the influx of calcium acts through intracellular cascades affectthe regulation of certain genes and the release of neurotransmitters.

Nicotinic AChRs are composed offive types of subunits:alpha (1-10), beta (2-5), delta, epsilon and gamma. Thesesubunits are found in different combinations in different types ofnicotinic AChRs:

Muscle nicotinic AChRs (adultneuromuscular junction): 1--1-1-

Muscle nicotinic AChRs (foetalextrajunctional): 1--1-1-

Neuronal nicotinic AChRs (CNS, PNS anddeveloping muscle): (7)5

Neuronal and autonomic nicotinic AChRs(ganglion): 3-4-3-4-4 and 3-2-3-4-5

Neuronal and autonomic nicotinic AChRs(brain): 4-2-4-2-2

Epithelial and neuronal nicotinic AChRs(cochlea hair cells): (9)5

These receptors span the membrane, containingextracellular, transmembrane and cytoplasmic domains, the latter

being the most variable. Nicotinic receptors are always pentamers,with the subunits arranged symmetrically around a central receptorchannel. The receptors always contain two or more alpha subunits,


26/35


which are critical in acetylcholine binding. The acetylcholine-

binding site is comprised of a dimer formed by the alpha subunits(principal component) plus an adjacent subunit (complementarycomponent), where binding to both sites is required for the channelto open.

Neurotoxins frequently target the acetylcholine-bindingsite, reversibly blocking the opening of the ion channel andformation of a pore, thereby preventing cations from passingthrough. Neuronal nicotinic AChRs have been divided into twomain groups based on their sensitivity to the snake venom toxin -bungarotoxin (Snake Venom: Bungarotoxins). The -

bungarotoxin-sensitive receptors are homomeric, containing 7 or9, and are found primarily in pre- and post-synaptic neurons andin developing muscle. The -bungarotoxin-insensitive receptors areheteromeric, containing combinations of 2-and and

which often modulate the release of other transmitters.

Alpha-Bungarotoxin:

-bungarotoxin is one of the components of the venom of theelapid snake Taiwanese banded krait (Bungarus multicinctus). It

binds irreversibly and competitively to the acetylcholine receptorfound at the neuromuscular junction, causingparalysis, respiratoryfailure and death in the victim.

The three-dimensional structureof -bungarotoxin. Disulfide

bonds shown in gold. FromPDB1IDI

Nicotinic receptor structure


27/35


In 1970, Changeux isolated the nicotinic acetylcholine receptor ofthe eel electric organ, the first ever isolated membrane

pharmacological receptor, that he was able to identify thanks to theproperties of a snake toxin. The isolation of the receptor was alsolater reported by Ricardo Miledi. The improvements of purificationmethods developed in the group allowed to propose that thereceptor was a pentameric protein, a finding quickly confirmed bythe team of Arthur Karlin. The group of Changeux was among thefirsts to elucidate the primary structure of the subunits of the

receptor, in parallel with the group of Shosaku Numan and StephenHeineman.The quest of Changeux for the structure of the nicotinicreceptor culminated recented with the publication of the structure,at atomic resolution, of a bacterial homolog in the openconformation supporting the idea of a symmetrical concertedopening.

Structure ofacetylcholine receptor

(pentamer)

Identification and

purification of the

nicotinic receptorfrom fish electric

organ: the first

membrane receptor for

neurotransmitter and ligand-gated ion channel to be

characterized as a protein (1970-1974)

In the late 60's, several groups (Chagas, Ehrenpreis, De

Robertis ...) had failed in their attempt to identify the acetylcholine


28/35


receptor because of the lack of physiological significance of their

binding data. Attempts had also been made to use labeling reagentsto isolate the receptor protein by Karlin and Changeux's groups, yet

with limited success (see B.7).To overcome this difficulty and

assess the specificity of cholinergic ligand binding, Changeux,

Kasai and Lee (1970) combined two biological systems: 1) toxins

purified from snake venoms by Lee and coworkers (1966), whichact as slowly reversible curares with a very high affinity and

selectivity on high vertebrate muscles and 2) the electric organ

from fish, a tissue recognized by Nachmansohn (1937) as

extremely homogeneous and rich in cholinergic synapses. They

made the seminal finding that a-bungarotoxin, a toxin from

Bungarus multicinctus venom is active on fish electric organ despite

the evolutive distance and the specialization of the tissue. It blocks

the electric response ofElectrophorus electrocyte to acetylcholine

and this effect is preserved, in vitro, on excitable microsacs

following the ion flux response (Changeux et al., 1970).

Moreover, Changeux, Kasai and Lee discovered that a-

bungarotoxin blocks, in vitro, the binding of reversible radioactive

cholinergic ligands to a macromolecule present in membranes

prepared from the electric tissue and solubilized by a non

denaturing detergent (deoxycholate). This macromolecule whichreversibly binds the cholinergic drugs was shown to be a protein,

distinct from acetylcholinesterase (Changeux et al., 1970, 1971)

and proposed to be the cholinergic receptor protein. The

solubilisation from the electric organ of Torpedo of an a-toxin


29/35


binding protein by the non denaturing detergent triton X 100 was

subsequently demonstrated by Miledi, Molinoff and Potter (1971,1972). The apparent molecular weight of the detergent solubilized

protein is close to 250,000 - 300,000 daltons (Meunier et al., 1971,

1974).

The protein was purified to homogeneity by Olsen,

Meunier and Changeux, 1972 and Meunier et al., 1974 from

Electrophorus electric organ. Purification was also achieved, in

parallel, in the Heibronn, Raftery, Karlin, Patrick, Reich ...

laboratories using jointly snake venom toxins andElectrophorus or

Torpedo electric organ.


30/35


About Jean-Pierre Changeux (A French neuroscientist discoverer ofNicotinic acetylcholine receptor)

Jean-Pierre Changeux

Born 7 April 1936 (age 73)Domont, France

Nationality France

Fields Neuroscience

Institutions Collge de France, Institut Pasteur

Alma mater cole Normale Suprieure , Pasteur Institute

Doctoral

advisorJacques Monod, Francois Jacob

Known for MWC model, isolation of nAChR

Notable awards Wolf Prize in Medicine (1982)

Changeux is author of more than 600 scientific articles and severalbooks, technical or for general audience. He was awarded


31/35


several Scientific prizes, awards, academic memberships

and honarary degrees.Scientific publications of historical significance

Monod J, Wyman J, Changeux JP (1965). On the nature ofallosteric transitions: a plausible model. Journal ofMolecular Biology 12: 88-118 (in which Jacques Monod,

Jeffries Wyman and Jean-Pierre Changeux presented theconcerted model of allosteric transitions, that explained thecooperativity exhibited by many allosteric proteins, suchas hemoglobin)

Changeux J.-P., Kasai M., Huchet M., Meunier J.-C.(1970). Extraction partir du tissu lectrique de gymnoted'une protine prsentant plusieurs proprits

caractristiques du rcepteur physiologique del'actylcholine. C. R. Acad. Sci. 270D: 2864-2867. (thefirst purification of a neurotransmitter receptor. Since thearticle is in French, most people quote the description ofthe toxin that allowed the receptor to be identified.

Changeux JP, Kasai M, Lee CY (1970). Use of a snake

venom toxin to characterize cholinergic receptor protein.Proceedings of the National Academy of Sciences USA67: 1241-1247).

Changeux JP, Courrege P, Danchin A (1973). Theory ofepigenesis of neuronal networks by selective stabilizationof synapses. Proceedings of the National Academy ofSciences USA 70: 2974-2978 (In which the authorsdevelop a formal model of synapse selection, precursor ofthe "neural darwinism". This is the original work, althoughmost people quote the subsequent review [better suited to anon-specialist audience and presenting the biologicalcontext]: Changeux JP, Danchin A (1976) Nature, 264(1976) 705712.)


32/35


Figure 2: Overview of signal transduction pathways


33/35


Figure 5. The primary acid-base catalysis reactionmechanism of cellobiose hydrolysis depicted in the form ofmodel showing glucose and BGA surrounded by hydrogenions (H

+) since the active center of BGA (Glu) is a

nucleophile(-ve) and thereby will not function under thiscondition (low pH , high hydrogen concentration) and sincethe Glu is not free to react but as soon as the pH rises it willrelease the hydrogen and readily release the glucose (G)from cellobiose (G-G). (A) BGA enzyme molecule depicted as

model (B) 6 hydrogen molecules shown (C) Glucosemolecule shown as pyranose form.http://www.picamatic.com/show/2013/06/07/05/17/9329529_640x480.jpg

A B C


34/35


References

1. Alberts et al, ed. 2002. Molecular Biology of the Cell.New York/London: Garland Publishing. 1616p.

2. Austin V. 2004. Fundamentals of the nervous system andnervous tissue. Pearson Education, Inc., Benjamin

Cummings. From, Marieb E.N. 2004. Human Anatomy &

Physiology, Sixth Edition. [1]

3. Gomperts, BD.; Kramer, IM. Tatham, PER. (2002). Signaltransduction. Academic Press. ISBN 0-12-289631-9.

4. http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&uid=3075366&cmd=showdetailview&indexed=google.

Retrieved on 2007-11-24.

5.

Kandel ER, Schwartz JH, Jessell TM. Principles of Neural

Science, 4th ed., pp.178-180. McGraw-Hill, New York

(2000). ISBN 0-8385-7701-6

6. Purves D., Augustine G.J., Fitzpatrick D., Katz L.C.,LaMantia A.S., McNamara J.O., and Williams S.M. 2001.

Neuroscience, Second Edition. Sinauer Associates, Inc. [2]

7. Schmitz D, Mellor J, Nicoll RA. Presynaptic kainatereceptor mediation of frequency facilitation at


35/35


hippocampal mossy fiber synapses. Science. 9 March

2001;291(5510):1972-6. PMID 11239159

8. The Human Plasma Membrane Receptome

(http://www.receptome.org).

9. Zimmerberg, B. 2002. Dopamine receptors: A

representative family of metabotropic receptors.

Multimedia Neuroscience Education Project.

Documents

A combination of structure with biological function: A signal transduction note