The Cytoskeleton. Intermediate Filaments 8-10 nm in diameter Four types: basis of aa sequence actin...

The Cytoskeleton

Intermediate Filaments

• 8-10 nm in diameter

• Four types: basis of aa sequence

• actin & tubulin -> globular protein, cell type specific• subunit of IF -> fibrous protein, wide range of size, nonpolar

• Around nucleus, extend out to cell periphery (by attachment of ut)

• Abundant in cells require mechanical stress:• epithelia, length of axon, cytoplasm of smooth muscle

Epidermolysis bullosa simplex

Amyotrophic lateral sclerosis (Lou Gehrig’s Disease) :accumulation and abnormal assembly of NF in motor neuron cell bodies and in the axon-> interfere axonal transport-> degeneration of axon-> muscle weakness and atrophy

A microtubule array can find the center of a cell

Dynamic + ends pointing outward and stable - ends collected the center

Dynamic instability

Effects of stathmin on microtubule polymerization

Organization of microtubule bundles by MAPs

The effects of proteins that bind to microtubule ends

Capping proteins help to localize microtubules

Microtubule motors

Dynein

Kinesin

Microtubules in cilium or flagellum

Ciliary dynein

The bending of an axoneme

Basal bodies

Kinesin and KRP

A model for the attachment of dynein to a membrane-enclosed organelle

Actin filaments

The tip of the leading edge of a cell nucleates actin filaments

Nucleation by the ARP complex

Web formation by the ARP complex

Actin Binding Proteins

Profilin bound to an actin monomer

Effects of thymosine and profilin on actin polymerization

Filament capping and its effects on filament dynamics

Actin array in a cell

Actin-cross-linking proteins

The formation of two types of actin filament bundles

A microvillus

Filamin cross-links actin filaments into a 3-D network with the physical properties of a gel

Filament severing and its effects on filament dynamics

A model for actin filament severing by gelsolin

Platelet activation

The role of ERM (ezrin, radixin, moesin)-family proteins in attaching actin filaments to the plasma membrane

Focal contacts and stress fibers in a cultured fibroblast

The effects of Rac, Rho, and Cdc42 on actin organization in fibroblasts

The Actin motors

Myosin

Myosin II

The Myosin II bipolar thick filament

The motor activity of the myosin head

Myosin superfamily tree

Comparison of the domain structure of the heavy chains of myosin types

Light-chain phosphorylation and the regulation of the assembly of myosin II into thick filaments

Skeletal muscle myofibrils

Organization of accessory proteins in a sarcomere

T tubules and the sarcoplasmic reticulum