17 - Regulation of Cell Migration

Question 1

What are Small GTPases?

Answer 1

They are signalling proteins and members of the G-protein family, they have a role in hydrolysing GTP, Some of them include:
- Arf, Ras, Rho Rab

Question 2

What is Ras?

Answer 2

A small GTPase responsible for cell proliferation, its also one of the largest groups of signalling proteins.

Question 3

What is Rab?

Answer 3

A small GTPase responsible for endosomal trafficking.

Question 4

What is Rho?

Answer 4

A small GTPase responsible for migration and the structure if the cells cytoskeleton.

Question 5

What is Arf?

Answer 5

A small GTPase responsible for membrane budding.

Question 6

What does GTPase signalling depend on?

Answer 6

The bound nucleotide

Question 7

What is unique about active Arf6?

Answer 7

It is inhibitory

Question 8

What controls the shape of the GTPase?

Answer 8

The P-Loop (phosphate binding loop)

Question 9

What happens when magnesium is removed?

Answer 9

The nucleotide falls off.

Question 10

what do the switch regions 1 and 2 do?

Answer 10

They along with their interactions help to bind the effectors.

Question 11

How do we detect an active GTPase?

Answer 11

By effector binding, they are evolved to be matched to the loops so they can detect whether the GTPase is active or inactive.

Question 12

What are the 2 steps in The catalysis of GTP hydrolysis?

Answer 12

1) The positioning of attacking water-
Which is carried out by catalytic glutamine and hydrolyses the
alpha-beta subunit.

2) Counteracting the negative charge at the phosphates.

Question 13

What are the active mutants in the catalysis of GTP hydrolysis and what do they do?

Answer 13

• The Q61L mutant which acts as a catalytic mutant.
• The G12V which pushes out the Q61 disturbing the P-loop.

Question 14

How do the mutants effect hydrolysis?

Answer 14

It reduces it 10-fold.

Question 15

What is the role of GEFs (guanine nucleotide exchange factors) in the cyclic regulation of GTPases?

Answer 15

• They speed up the transition of GTP to GDP
• They stabilise nucleotide free, magnesium free GTPases.

Question 16

What is the role of GAPs (GTPase activating proteins)?

Answer 16

They activate the hydrolysis function and so turn off the signalling.

Question 17

What is the role of GDIs (Guanine nucleotide dissociation inhibitors)?

Answer 17

They bind to GTPase and hold it in the cytosol, then switch it off

Question 18

What regulates actin based motility?

Answer 18

Rac

Question 19

What small GTPase is responsible for the contractility in actin based motility?

Answer 19

RhoA

Question 20

What happens if a growth factor is used to stimulate migration?

Answer 20

The cell will move towards the growth factor.

Question 21

What structure helps to move the cell towards the growth factor?

Answer 21

Filipodium.

Question 22

What Small GTPase causes the growth of the filipodium towards the growth factor?

Answer 22

Cdc42

Question 23

What small GTPase is responsible for the growth of lamellopodia (Protruion) and the formation of new adhesions towards the growth factor?

Answer 23

Rac1

Question 24

What small GTPase is responsible for the formation of actin stress fibres (contractility) pulling forward the body of the cell?

Answer 24

RhoA

Question 25

What are the 2 protrusive signals?

Answer 25

Cdc42 and Rac

Question 26

What is the contractile signal?

Answer 26

RhoA

Question 27

How do the protrusive and contractile signals work together?

Answer 27

They work against each other, backwards and forwards to get the cell moving forward.

Question 28

What does migration guidance do for the cell?

Answer 28

Helps them to translocate more efficiently.