lec 5- cytoskeleton: actin 2

Question 1

what are the 4 actin based structures?

Answer 1

1. lamellipodia
2. filopodia
3. stress fibers
4. microvilli

Question 2

what is lamellipodia used for?

Answer 2

whole cell motility

Question 3

what is lamellipodia?

Answer 3

very thin protrusions that are 0.25 micrometers thicka t the leading edge of the movement

Question 4

what is lamellipodia made of?

Answer 4

structure made of membrane and primarily Arp 2/3 branched actin

Question 5

where does actin polymerization occur in lamellipodia?

Answer 5

at the membrane esurface

Question 6

is actin branching in lamellum random?

Answer 6

no, it is specific at a 70 degree angle, all due to the Arp 2/3 complex

Question 7

what is the Arp 2/3 complex and what does it do?

Answer 7

-an actin nucleator which binds to the sides of preexisting actin filaments
-caps and nucleates the pointed ends of new filaments

Question 8

how many proteins make the Arp 2/3 complex?

Answer 8

-7 proteins
-Arp 2 and Arp3 bind to ARPC1-ARPC5

Question 9

why is Arp 2 and Arp 3 able to lend itself to actin branched networks to be the first 2 subunits at the pointed ends?

Answer 9

-because Arp 2 and Arp 3 are structurally similar to actin
-they all act as pseudodimers

Question 10

when an actin monomer binds to the pseudodimers, it effectively gives rise to what?

Answer 10

a trimer that is used in normal actin filament polymerization

Question 11

what does Arp 1 do?

Answer 11

it is not a part of the Arp 2/3 complex, rather it is part of the dynactin complex

Question 12

what activates the usually inactive Arp 2/3 complex?

Answer 12

nucleation promoting factors

Question 13

what are the 2 nucleation promoting factors?

Answer 13

1. WASp (Wiscott Aldrich Syndrome protein)
2. SCAR/WAVE

Question 14

what is the structure of WASp made of?

Answer 14

adaptor protein domains that link the signaling cascades to actin filament polymerization

Question 15

what are the domains of WASp and what do they do?

Answer 15

EVH1: bind to proline-rich regions of proteins that bind to WASp
Basic: binds to PIP2 (a phospholipid)
GBD: binds to Cdc42-GTP
Proline-rich: binds to other proteins containing SH3 domains
V (verprolin): bind to 1 actin monomer
C (cofilin) and A (acidic): together bind to Arp 2/3 complex

Question 16

how do the VCA domains activate the Arp 2/3 complex?

Answer 16

they cause a conformational change spacing out Arp 2 and 3 perfectly to nucleate actin

Question 17

what does the Ena/VASP family do?

Answer 17

-stimulates actin filament elongation
-protects filaments from capping
-binds near the barbed end of filaments
-enhances the delivery of profilin-actin to the barbed ends of the filaments
-increase the speed of actin based movements

Question 18

what is the structure of Ena/VASP?

Answer 18

-2 EVH domeains
-proline-rich region
-actin binding domains
-coiled-coil domain

Question 19

where are Ena/VASP found?

Answer 19

-at cell-cell junctions called adherens junctions
-the leading edge of motile cells
-actin-rich structures called filopodia
-cell substratum attachments

Question 20

when is WASp autoinhibited?

Answer 20

-when not in use by the interaction of the basic and GBD domain
-not interacting with the VCA domains

Question 21

what activates WASp and what occurs?

Answer 21

Cdc42-GTPase, causes WASp to open, exposing its binding sites for other proteins to interact with actin and the Arp 2/3 complex

Question 22

what are the 3 proteins known as WAVE 1,2, and 3?

Answer 22

WH2 containing proteins

Question 23

where is the only WH2 domain found in WAVE?

Answer 23

found in the verprolin (V) domain

Question 24

what are the other 4 proteins in the larger complex that WH2 is in?

Answer 24

Sra1, Nap 1,Abi 2/3, and HSPC300

Question 25

what happens if any of the proteins in the same complex as WH2 are missing?

Answer 25

the complex will break apart and be degraded by the proteasome

Question 26

does the large WH2 complex have VCA domains?

Answer 26

yes, needed to activate Arp 2/3 complex via the small GTPase Rac

Question 27

what are Spire and Cordon-Bleu?

Answer 27

WH2 containing proteins

Question 28

what does Spire do?

Answer 28

-it is a monomer that can dimerize

Question 29

where are the 4 WH2 domains found in Spire? why are the domains needed?

Answer 29

-at the center of the protein -the domains are needed for the nucleation activities of Spire

Question 30

what in Spire is needed to nucleate actin?

Answer 30

the linker between WH2 domains 3 and 4

Question 31

what do the WH2 domains in Spire do?

Answer 31

help stabilze linear arrays of actin filaments

Question 32

was Spire the first protein shown to nucleate actin polymerization using a different mechanism than forming or Arp 2/3?

Answer 32

yes

Question 33

what does the Spire KIND domain interact with?

Answer 33

the C-terminal tail of Formins (e.g. cappuccino)

Question 34

how does Spire bring in 8 WH2 domains to help polymerize 2 actin strands?

Answer 34

Spire dimerizes upon its interaction with formin, causing it to bring 8 WH2 domains into play

Question 35

how many WH2 domains does Cordon-Bleu have?

Answer 35

3 WH2 domains at the C-terminus of the protein

Question 36

what type of linker does Cordon-Bleu have? Does the linker have an effect on the nucleation activities?

Answer 36

a long linker between the 2nd and 3rd WH2 domains, but has no effect on nucleation activities

Question 37

what is the 3rd WH2 domains used for in Cordon-Bleu?

Answer 37

it is used to position the third actin for trimer formation

Question 38

what is needed at the adjacent position of the first WH2 domains in Cordon-Bleu for nucleation to occur?

Answer 38

K domain