Lesson 20: Cytoskeleton 3: Actin

shape

actin allows cells to change _____

atpase

Is actin an atpase or gtpase

out, in

Actin has 4 subdomains:

1 and 3 are similar

ATP binds at the center of the molecule (hydrolusis occurs within the protein itself)

1 and 2 face —-ward but 3 and 4 face —-ward

T, D

Actin and microtubule plus end: A__P state, minus end: A__P state

L

Actin form:

filopodium: low capping activity, extends

lamellipodium: high capping activity, at membrane

Arp 2/3 form a branched network in the (F or L)

D

Actin sequestering: Profilin (induced G-actin nucleotide exchange)

profilin binds to A__P bound G-actin and induces nucleotide exchange

-AKA binds to the hinge region to stabilize a more open fonformation of the binding pocket, so ADP can leave and ATP can enter

add

Actin Polymerization: Formins ___ subunits to the filament PLUS end in filopodia

-parallel bundles of actin filaments cross linked, engage the membrane and localize to the tip of the filopodia

plus

Actin Capping: capping proteins vs. anticapping proteins

-Capping: bind and stabilize F-actin ____ end

D

Actin Severing: Cofilin

-binds regions of A_P-actin

-induces structural changes in lattice that sever at junctions btw regions

plus, minus

Drugs that affect Actin Dynamics:

1. phalloidin - binds to filaments and prevents depolymerization

2. Cytochalasin - caps filament ____ ends, prevent polymeriz and depoymerized filament at ___ ends

3. Latrunculin - binds actin monomers and prevents polymeriz

shape, movement

Actin 2 major functions:

1. assemble into scaffolding giving cell _____

2. generate forces during cellular ________

ARP

Actin polymerization at membranes in lamellipodia:

1. ___ inactive until binds to a mother actin filament

2. ARP nucleates growth of new actin filament at 70 degree angle

3. daughter filament grows and pushes membrane forward

4. polymeriz of daughter filament stopped by capping protein

5. mother filament is hydrolyzing ATP as it ages (signal for cofilin to bind and trigger disassembly)

6. monomeric actin released from depolym mother filament, binds to ATP, diffuses to front of cell to restart process

membrane

F-actin structures activated by Rho GTPases that are ______-associated