G Proteins

Question 1

What are G proteins considered since they are controlled by two apposing enzymes?

Answer 1

conformational switches

Question 2

Where do G proteins get their name?

Answer 2

G = guanine; named for their ability to bind to guanine nucleotides

Question 3

In the conformational switch of G proteins, which “writer” switches GDP to GTP?

exchange

Answer 3

GEF

to ON state

Question 4

In the conformational switch of G proteins, which “eraser” switches GTP to GDP?

hydrolysis

Answer 4

GAP

to OFF state

Question 5

The binding of ____ to GTP triggers the GTP to form products.

Answer 5

effectors

Question 6

Which phosphate on GTP plays a critical role in controlling G protein conformation?

Answer 6

gamma phosphate

it is typically the one that is hydrolyzed

Question 7

On the molecular based of G protein conformation change, which two residues are held together by a third phosphate?

Answer 7

Gly (glycine) and Thr (threonine)

this forms GTP

Question 8

How many G proteins does a typical eukaryotic cell contain?

Answer 8

~150

Question 9

The G protein superfamilies consist of…

Answer 9

• small G-protein
• heterotrimeric G-proteins

Question 10

What does GEF stand for?

Answer 10

Guanine-nucleotide exchange factor

Question 11

What does GAP stand for?

Answer 11

GTPase-activating protein

Question 12

The rate of the nucleotide exchange reaction and the nucleotide hydrolysis reaction are kinetically controlled by ____ and ____.

Answer 12

GEFs and GAPs

Study this figure

Question 13

What factor controls the activity of GEFs and GAPs to control specific GTPase action?

Answer 13

upstream signaling inputs

Question 14

What are the small G protein subfamilies and their respective function?

Answer 14

• Ras - cell proliferation/differentiation
• Rho - cell shape/movement
• Rab - vesicles
• Arf- vesicles
• Ran - nuclear import

Question 15

Which small G protein is responsible for contraction in cell mobility?

Answer 15

Rho

RhoA - formation of actin-myosin contractile structure

Question 16

Which small G protein is responsible for protrusion in cell motility?

Answer 16

Rac

Rac I - formation of actin-based protrusion

Question 17

Which G protein is responsible for stress fibers?

Answer 17

Rho

Question 18

Which G protein is responsible for lamellipodia?

Answer 18

Rac

Question 19

Which G protein is responsible for filopodia?

Answer 19

Cdc42

Question 20

What is this?

Answer 20

G-protein coupled receptor (GCPR)

Question 21

What does this depict?

Answer 21

1) ligand binds to GCPR
2) Nucleotide exchange between alphaG by GCPR
3) Activated alphaG dissociates from betaG and gammaG
4) each binds to effectors to produce outputs

Question 22

Activated GCPRs act as ____ to add phosphate to GDP.

Answer 22

GEF

Question 23

Regulators of G protein Signaling (RGS) proteins serve as ____ to counteract the GCPR.

Answer 23

GAPs

Question 24

Rho GEFs and GAPs serve as an ____ ____ that allows upstream inputs to plug into common G-protein mediated output responses.

Answer 24

adaptor layer

Question 25

Many GEFs and GAPs are ____ and can dictate specific protein and lipid interactions.

Answer 25

modular

Question 26

What does this depict?

Answer 26

GEF and GAP catalytic domain recruitment to the sites of G protein action

Question 27

What does this depict?

Answer 27

Activiation by relief of **auto inhibition** via ligand binding or phosphorylation

Question 28

What does this depict?

Answer 28

Activation of RhoGEF by ligand binding

Question 29

Most G proteins bind both GTP and GDP with high affinity and have half-times for dissociation in ____ to ____.

Answer 29

minutes to hours

Question 30

How do GEFs generally act in a mechanism?

Answer 30

They modify the structure of the nucleotide binding pocket, resulting in **reduced affinity** for the nucleotide binding.

Question 31

How does GTP bind to the G protein after interacting with GEF?

Answer 31

It is driven by the much higher intracellular concentration of GTP

Question 32

What is the mechanism of GAP?

Answer 32

GAP binds to active GTP and with the hydrolysis from a water molecule, causes the removal of a phosphate, creating GDP.

Question 33

When GAP interacts with the G protein binding pocket, what is the the known structure that associates with GAP?

Answer 33

**arginine finger** stabilizes the phosphate in the G protein pocket

Question 34

Many G protein have ____ ____ attached at the C-termini for membrane localization and function.

Answer 34

lipid groups

Question 35

Binds to specific G protein and shields the lipid group to maintain the G protein in the cytoplasm; locks in its GDP bound form and prevents their localization to the membrane.

Answer 35

guanine nucleotide dissociation inhibitors (GDIs)

Question 36

Promotes the release of GDI from G protein, allowing G protein localization to membrane.

Answer 36

GDI displacement factors (GDFs)

Question 37

permanent lipid attachment

Answer 37

integral protein

Question 38

What does the MAP kinase cascade do?

Answer 38

After an input, the **MAPKKK** becomes phosphorylated, after entering a new cycle, it loses a K, **MAPKK** becomes phosphoylated, enters a cycle and loses a K, then finally **MAPK** is phosphorylated and produces an output.

Question 39

How do scaffolds work with MAPK cascades?

Answer 39

They help to physically organize the MAPK components

Question 40

What mechanism of scaffold proteins controlling information flow is being depicted below?

Answer 40

increasing the effective concentration of two interactive proteins through **tethering** and enhanced proximity

Question 41

What mechanism of scaffold proteins controlling information flow is being depicted below?

Answer 41

preventing the protein from interacting with alternative partners and substrates

Question 42

What mechanism of scaffold proteins controlling information flow is being depicted below?

Answer 42

the scaffold itself may serve as an allosteric regulator to make a pathway protein active upon binding to scaffold (inactive without scaffold interaction)