GPCR Signalling

Question 1

Name two G- Protein systems

Answer 1

GCPR (7 TMS receptors) and Trimeric G Proteins

Question 2

Whats are some attributes of GCPRs

Answer 2

• only found in eukaryotes
• involved in cAMP and phosphotidylinosital signaling
  *Has 7 transmembrane domains
  *has a glycosylated ligand binding region
• has a site between 5 and 6 where interactions happen.
  has a a row of gly residues on the tail that can be phosphorylated
  *the receptors control what pathways are activated

Question 3

What are some attributes of trimeric G proteins?

Answer 3

there are 3 subunits, when activated the alpha unit dissociates leaving the beta and gamma as a dimer.

Question 4

G protein signalling overview

Answer 4

1. ligand binds GCPR
2. Conformational change happens. this change switches on g protein associated with receptor, allowing for guanine exchange to happen.
3. G protein swaps GDP for GTP, causing alpha to dissociate from beta and gamma
4. alpha activates target
5. alpha has intrinsic activity that hydrolyses GTP for GDP, rendering alpha inactive

Question 5

Can the ligand dissociate from the binding site and still have G alpha bind to a. cyclase

Answer 5

Yes

Question 6

What do G proteins do?

Answer 6

They amplify signals/enzyme amplification

Question 7

Can one G protein activate multiple receptors?

Answer 7

yes, and one receptor can activate multiple G proteins

Question 8

True or False: active G proteins induce effector protein to make second messenger as long as Galpha GTPase exists

Answer 8

True

Question 9

True or False: G proteins can both activate and inhibit a. cyclase

Answer 9

True

Question 10

When G alpha is bound to a cyclase _______ is produced

Answer 10

No cAMP is produced, GTP to GDP swap

Question 11

What is another method of cAMP regulation

Answer 11

G protein a cyclase inhibition (Galphai)

Question 12

A cyclase can form a complex with___

Answer 12

beta and gamma subunits

Question 13

what are some functional aspects of a cyclase

Answer 13

• it is a dimer with 2 transmembrane domain(M1,M2) and 2 catalytic domains (C1,C2)

Question 14

How many helices are in A cyclases transmembrane domains

Answer 14

6 per domain, 12 total

Question 15

Can the beta gamma subunits precouple?

Answer 15

yes, they can pre couple with the N terminus of the transmembrane domain

Question 16

Where does the catalytic site form on A cyclase

Answer 16

between C1 and C2 domains

Question 17

Gs alpha binds to ____ and Gi alpha binds to _____

Answer 17

Gsalpha binds to C2 and Gialpha binds to C1

Question 18

Gsalpha___ the formation of C1,C2 complex

Answer 18

stimulates

Question 19

Gialpha___ the formation of C1,C2 complex

Answer 19

inhibits, furthermore inhibits the creation of cAMP

Question 20

How do trimeric G proteins regulate a. cyclase activity

Answer 20

• Gialpha inhibits a cyclase from producing cAMP because it prevents dimerization
  -Gsalpha stimulates a cyclase dimerization. this creates an active catalytic site where ATP it converted into cAMP
• C1and C2 subunits are only active when dimerized

Question 21

What is the collision coupling model for G protein receptor activation of A cyclase

Answer 21

This takes place over seven steps:
1. the G protein is inactive, the ligand is unbound
2. ligand binds to receptor, conformational change happens, G protein binding region is now exposed
3. Ligand is bound and G protein is bound, GDP is swapped for GTP. G protein has conformational change and its subunits dissociate
4. ligand is no longer bound, G protein is still dissociated. GTP is still bound, allows for alpha subunit to bind to a cyclase
5. GTP is still bound and alpha subunit is still bound to a cyclase. ATP is converted into cAMP. GTP can. be converted into GDP via hydrolysis
6. GDP is now bound to alpha subunit, a cyclase is no longer producing cAMP
7. alpha subunit dissociates with a cyclase and reforms with beta and gamma.

Question 22

How do kinases regulate GCPR activity

Answer 22

-GCPRS have tails that have phosphorylate-able residues on them. Some PKs such as Cam Kinase 2 can Pi specific sites to desensitize GCPRS when there are overactive due to high ligand concentrations.

-Pi of PKA can block G protein binding and activation. Some GCPRs can induce a switch in G protein coupling from Gs to Gi

• the most important regulators of GPCR signaling are the CPCR kinases, GRKs. Pi of the GCPR tail by GRK1/2 results in beta arestin recruitment and internalization of the GCPR. Pi by GRK5.6 also results in beta arestin recruitment but induce binding and activation of ERK MAP kinase pathway

Question 23

What is based agonism?

Answer 23

GPCR signaling can be activated by G alpha subunits of trimeric G protein to induce second messenger production by effector proteins or by trimeric G protein beta gamma subunit activation of beta arrestin activation of ERK MAP kinase pathway.

Different agonist (ligand) acting on the same GCPR can induce second messenger activation (cAMP, IP2, Ca2+, DAG) or MAP kinase/ ERK activation.

Biased agonism refers to the bias in which a pathway is activated. with some agonists being balanced in both second messenger signaling and beta arrestin signaling. Some ligands are predominantly active in either second messenger or beta arrestin signaling. some GCPRs themselves are biases toward beta arrestin signaling for all ligands

Question 24

How are GCPR kinases recruited to GCPR

Answer 24

beta gamma subunits, this is there main function

Question 25

Where do GPCR kinases phosphorylate?

Answer 25

the c terminus of the GCPR, this is what regulates there activity

Question 26

What can GCPR phosphorylation cause?

Answer 26

1. reduced GCPR signaling
2. Internalization and recycling of GCPR (a ligand can be sent back to cell surface or internalized where its desensitized)
3. GCPR can be degraded in the proteasome
4. it can activate MAPK and ERK signaling (MOST IMPORTANT)
5. It can alter G protein coupling: some sites on tail can be Pi by PKA, allowing Gs to bind to Gi

Question 27

Balanced Signaling

Answer 27

A ligand that activated both pathways equally

Question 28

BA biased ligand

Answer 28

-Ligands that are biased toward the BA pathway
-Some 2nd messenger activity but not as much

Question 29

BA biased receptor

Answer 29

Independent of ligand the receptor is BA based

Question 30

what is beta arrestin?

Answer 30

a protein that blocks GPCR signaling. it links to clathrin via AP2 and targets things to the endosome.