actin Flashcards

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1
Q

what are the main types of actin accessory proteins?

A
polymerizing
nucleating
bundling
capping
severing
gelating
motor proteins
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2
Q

what are polymerizing proteins? example

A

they add actin monomers to the filament. Profilin adds to the plus end

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3
Q

what are nucleating protein? example

A

they allow the cell to control the time and place of de novo actin filament assemble. Arp2/3 and Formin nucleate actin filaments in vivo

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4
Q

What do Profilin and Formin do and how?

A

together they add actin monomers to the plus end of the filament. Formin proteins have long whiskers that bind profilin-actin complexes which adds actin to filament end. Formin only nucleates unbranched filaments

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5
Q

what is the difference between Formin and Arp2/3?

A

Formin nucleates unbranched filaments

Arp2/3 nucleates branched filament networks. always creates a 70 degree angle in branches

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6
Q

what did Arps arise from?

A

gene duplication and divergence of actin. Arps are 45% identical to actin in amino acid structure

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7
Q

how do Arps work? describe steps in process

A

Arp is activated by a signaling protein and will come together with other proteins to form a complex. The complex attaches to the side of a filament and adds actin monomers in branches at 70 degree angle to the original filament

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8
Q

How can bacteria exploit actin polymerization?

A

the assembly of actin on a bacterias back surface propels the bacterial forward, helping them invade neighboring cells and maintain infection. Listeria monocytogenes is an example of bacteria doing this

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9
Q

what are capping proteins?

A

they stabilize actin filament length and inhibit further elongation. They can bind to either the plus or minus end

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10
Q

what are severing and depolymerizing proteins? example

A

they accelerate the disassembly of actin filaments by severing and depolymerizing. Cofilin

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11
Q

how does Cofilin work?

A

Cofilin binds to actin filaments and increases the apparent twist, weakening non covalent bonds and destabilizing filament.

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12
Q

what are bundling proteins?

A

they organize actin filaments into bundles. some pack them tightly and some loose.

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13
Q

what are cross linking proteins? example

A

they connect actin filaments into lattice like structures important for cell crawling (filopodia and pseudopodia). Filamin

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14
Q

what diseases can be caused from defective filamin?

A

Periventricular Heteropia is caused by a mutation in filamin A gene. This causes failure of neurons to migrate during development and patients often have epilepsy.

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15
Q

what causes Duchenne Muscular Dystrophy?

A

mutation of the protein Dystrophin, a cross linking protein

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16
Q

what are motor proteins? example

A

they can form contractile structures of the actin cytoskeleton. Myosin

17
Q

what is myosin structure?

A

a motor protein with two globular heads and a tail, result of dimerization of two heavy chains.

18
Q

how does myosin work?

A

myosin heads bind and hydrolyze ATP. This causes conformational changes that lead to walking of the heads along actin filaments. Then ADP is released and the original conformation is restored, moving back to this conformation involves a “power stroke” which moves the filament

19
Q

what do the myosin tails do?

A

myosin tails can come together and aggregate. they bundle into thick bipolar filaments. the bipolar arrangement allows for sliding of actin filaments together, contributing to muscle contraction.