Lecture 2 - More Actin Flashcards

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1
Q

Actin-binding proteins function through regulatory mechanisms that assemble/disassemble the actin filaments. Provide examples.

A
  1. Inhibition of the spontaneous polymerisation of G –> F actin.
  2. Nucleation of new actin filaments.
  3. Control of length.
  4. Elongation/shortening of pre-existing actin filaments.
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2
Q

Provide two examples of actin-monomer binding proteins that regulate polymerisation.

A

Thymosin beta 4 and profilin.

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3
Q

Thymosin Beta 4.

A

Sequesters G-actin, preventing polymerisation and nucleotide exchange.

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4
Q

Profilin.

A

Binds to G-actin and increases the rate of nucleotide exchange. Only prevents polymerisation at the (-) end.

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5
Q

Provide two examples of actin-monomer binding proteins that regulate nucleation.

A

Formins and the Arp 2/3 complex.

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6
Q

Formins.

A

Bring 3 monomers together to promote the formation of the tri-actin nucleus.

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7
Q

Arp 2/3 complex.

A

ARP = Actin Related Protein. 5 other subunits involved. As well as nucleation, also promotes the branching of MFs.

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8
Q

Actin-filament binding proteins can be capping or severing. Name two examples.

A
Capping = gelsolin. 
Severing = cofilin.
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9
Q

Function of gelsolin?

A

Binds to F-actin at the (+) end –> uncapped (-) end can disassemble. Has the ability to dissolve an actin filament.

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10
Q

Function of cofilin?

A

Also called ADP-cofilin, which stands for Actin Depolarising Factor. Binds to ADP-actin, either free as G-actin or at the (-) end. If it binds to the (-) end then it can increase polymerisation. If it binds deeper into the filament = severing.

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11
Q

Actin-filament binding proteins orchestrate higher order actin architectures. These are cross linking proteins. Name some of the structures and the formation the actin filaments take.

A

Stress fibres = antiparallel contractile structures that are orchestrated by alpha-actinin.
Cell cortex = branched network orchestrated by filamin.
Filopodium = tight parallel bundles orchestrated by fimbrin.

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12
Q

Describe the structure of the protein fimbrin.

A

Monomeric protein with 2 actin binding domains. Each domain can bind to a filament, giving rise to the tight parallel bundles of filopodia.

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13
Q

Describe the structure of the protein alpha actinin.

A

It is a dimeric protein; 1 actin binding domain. They form a head-to-tail structure which is responsible for the antiparallel nature of the stress fibres.

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14
Q

Describe the structure of the protein filamin.

A

It is a dimeric protein; 1 actin binding domain. Form a ‘V’ shape, which is responsible for organising the filaments into branched structures.

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15
Q

Name two specialised cross linkers.

A

Spectrin and dystrophin.

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16
Q

Structure and function of spectrin?

A

Tetrameric; forms the meshwork that gives RBCs their shape.

17
Q

Structure and function of dystrophin?

A

Monomeric; part of a multi-protein complex that connects muscle fibre cytoskeleton to the e. matrix. Plays a key role in force generation in muscle.

18
Q

General structure of myosins?

A

They consist of 1 or 2 heavy chains in a complex with light chains. They have a globular head region that binds actin. ATPase activity generates force to walk.

19
Q

Which myosins interact with the cytoskeletal membrane?

A

I and V.

20
Q

Which myosin group is involved in muscle contraction?

A

II.