lec 9-10. GPCRs

Question 1

PAR receptors

Answer 1

Receptor for thrombin which is important in blood clotting
Thrombin is a protease, it cleaves amino terminus, and then goes off. Remaining amino terminus goes into ligand binding site to activate receptor

Question 2

GTPase

Answer 2

convert GTP -> GDP

Question 3

Structure of GPCRs

Answer 3

7 TMDs

ligand binding (deep within receptor) + amino acids allow TM3 which is central to release energy and allow TM5 and TM6 to move

N’ terminus contributes to ligand binding
C’ terminus contributes to receptor function

Question 4

GPCR resting state

Answer 4

G-protein is anchored in PM, Ga bound to GDP

Question 5

GPCR active state

Answer 5

Ga bound to GTP, dissociated from beta/gamma subunits

Question 6

Monomeric G protein

Answer 6

they are small GTPase. GEF releases GDP to allow it to bind GTP and become active. Its timing is controlled by GAP

Question 7

Guanine Exchange Factor (GEF)

Answer 7

stimulate release of GDP to allow binding to GTP

Question 8

GTPase Activating Protein (GAP)

Answer 8

bind to G-proteins and stimulate their GTPase activity with the result of terminating signalling event.

Question 9

Heterotrimeric G proteins

Answer 9

have alpha, beta, and gamma subunits. in resting state, Ga is bound to GDP. in active state, the receptor itself acts a GEF to release GDP and allow it to bind to GTP to become active. The subunits dissociate and go on to effect enzymes downstream. Signalling ends when RGS activates the GTPase activity of Ga to hydrolyse GTP into GDP

Question 10

Regulator of G-protein Signalling (RGS)

Answer 10

a GAP which activates the GTPase activity of heterotrimeric alpha-subunits

Question 11

second messengers

Answer 11

intracellular signalling molecules released in response to binding of extracellular signalling molecule to a receptor

Question 12

message is encoded in…

Answer 12

concentrations of second messengers and frequency of changes in concentration

Question 13

concentration of second messenger is determined by…

Answer 13

rate of production, rate of diffusion from origin, and rate of removal

Question 14

GsPCR Pathway

Answer 14

Gsα -> adenylate cyclase -> cAMP -> PKA -> phosphorlates calmodulin phosphorylase kinase -> phosphorylates phosphorylase P > converts glycogen into glucose 6-phosphate

Question 15

factors limiting signalling pathway

Answer 15

• GTPase activity of alpha subunit
• Gs beta and gamma subunits recruit kinases which phosphorylate the receptor, making it attractive to B-arresting, stopping signalling

Question 16

lipases

Answer 16

hydrolyzes membrane lipids to generate IP3 and DAG

Question 17

lipid kinases

Answer 17

adds phosphates groups on:
DAG to make phosphatidic acid
PI to make PIP, PIP2, PIP3

Question 18

PIP2

Answer 18

broken down by phospholipase C (PLC) to make IP3 and DAG

Question 19

IP3

Answer 19

interacts with IP3 receptors on ER to release Ca+ into the cytosol -> Ca+ signals can sum up with Ca+ signals from other receptors

Question 20

DAG

Answer 20

regulates PKC in the plasma membrane

Question 21

GqPCR Pathway

Answer 21

Ga+Gby activate PLCβ to breakdown PIP2 into IP3 and DAG

Question 22

Phospholipase C (PLC)

Answer 22

breakdowns PIP2 into IP3 and DAG

PH domain anchors enzyme
C2 & EF domains are Ca+ binding

Question 23

protein kinase A (PKA)

Answer 23

regulated by cAMP, uses ATP to phosphorylate Ser and Thr calmodulin phosphorylase kinase

Question 24

protein kinase C (PKC)

Answer 24

structurally similar to PKA but regulated by DAG and Ca+

Question 25

activation of PKC

Answer 25

DAG binding causes dissociation of intramolecular pseuosubstrate domain

Question 26

deactivation of PKC

Answer 26

sensitive to breakdown of DAG

Question 27

calsequestrin and calreticulin

Answer 27

bind to Ca+, allowing high levels of Ca+ to buildup in the ER