Lecture 12- GPCRs

Question 1

What is signal transduction?

Answer 1

Receptors needed for cells to respond to extracellular signalling molecules (hormones, NT, GF)

Question 2

receptors can be

Answer 2

intramembrane (majority) or intracellular

Question 3

how many types of GPCR identified in human genome

Answer 3

> 800 (>2% of identified genes)

Question 4

structure of GPCRs

Answer 4

• Single peptide sequence (300-1200 amino acids)
• 7 transmembrane structures
• N terminal outside the cell
• C terminal faces inside the cell

Question 5

N terminal

Answer 5

outside the cell- ligand binding domain

Question 6

c terminal

Answer 6

faces inside the cell- Gprotein

Question 7

where do ligands bind on GOCR

Answer 7

two different sites:

• binding site on N-terminal region
• bidding site in transmembrane

Question 8

each receptor subtype is specific for

Answer 8

one chemical ligand

Question 9

ligand binding activates the receptor which directly or indirectly

Answer 9

brings about change in the cellular activity

Question 10

percentage of prescription drugs that exert their therapeutic effects directly or indirectly at the GPCRs

Answer 10

40%

Question 11

agonists

Answer 11

bind and activate

• Leading to intracellular signal transduction

Question 12

example of a GPCR agonist

Answer 12

salbutamol (B adrenoreceptor agonists)

morphine (u-opioid receptor agonist)

Question 13

antagonists

Answer 13

bind and block the effect of agonist on the receptor

Question 14

example of a GPCR antagonist

Answer 14

cardiovascular (hypertension) B-adrenoreceptorsantagonists

Question 15

what can GPCRs respond to

Answer 15

1) Sensory GPCRs- light, odours and taste
2) Ions
3) NT
4) Peptide (glucagon, insulin, adrenaline) and non-peptide hormones
5) Large glycoproteins- TSH

Question 16

G protein is made up of three different proteins

Answer 16

Alpha and Beta/Gamma(single unit)

Question 17

activation of the GPCR facilities activation of G protein on the inside of the membrane..

Answer 17

1. When adrenaline binds the GPCR changes its conformation- initiation of cascade
2. Conformational change attracts G protein, which is activated
   a. Alpha Part of G-protein bound to GDP
3. G protein activated- exchanges GDP for GTP
4. Once GTP is bound to alpha subunit it dissociates from the beta and gamma subunit- leaving a free alpha-GTP and free B/Y subunit which both have effector role

Question 18

Termination of G-protein signalling

Answer 18

1. GTPase hydrolyses the GTP that’s bound to the alpha submit releasing Pi returning alpha to Alpha-GDP state- no effector function
2. Alpha-GDP ready to be reactivated by GPCR

Question 19

Where is the G protein (Alpha and beta-gamma subunit) found

Answer 19

inserted in the cell membrane uses plasma membrane as a monorail to move around in the plane of the membrane

Question 20

types of G protein

Answer 20

GalphaS
GalphaI
GalphaQ

Question 21

human genome encodes how many Ga proteins

Answer 21

20

Question 22

human genome encodes how many GB proteins

Answer 22

5

Question 23

human genome encodes how many GY proteins

Answer 23

12+

Question 24

how many Ga-BY combinations

Answer 24

over 1000

Question 25

G protein diversity means that

Answer 25

an extracellular signal, working via a specific GPCR, will activate a single, or small sub-population of G proteins and effectors in the cell to bring about a specific cellular response.

Question 26

alpha1 receptor

Answer 26

Q - stimulate phospholipase C - increase IP3 and DAG

Question 27

alpha 2 receptor

Answer 27

I - decrease adenylyl cyclase activity - decrease cAMP

Question 28

beta 1 receptor

Answer 28

S - increase adenylyl cyclase activity - increase cAMP

Question 29

beta 2 receptor

Answer 29

S - increase adenylyl cyclase activity - increase cAMP

Question 30

M1 receptor

Answer 30

Q - stimulate phospholipase C - increase IP3 and DAG

Question 31

M2 receptor

Answer 31

I - decrease adenylyl cyclase activity - decrease cAMP

Question 32

M3 receptor

Answer 32

Q - stimulate phospholipase C - increase IP3 and DAG

Question 33

M4 receptor

Answer 33

Q - stimulate phospholipase C - increase IP3 and DAG

Question 34

interfering with G-protein function

Answer 34

target the GTPase enzyme

Question 35

which toxins are used to study GPCR-G- protein signaling

Answer 35

vibrio cholera pertussis toxin (Ptx)

Question 36

vibrio cholera

Answer 36

covalent modification of αs subunit  Stops the αs from turning itself off • Can undergo GDP for GTP exchange • Can signal • But cannot turn itself off via GTPase  Causes sustained αs mediated signal- causing overactivation of adenylyl cylase- increase in [cAMP]  High [cAMP] opens water channels- releasing water and electrolytes into the lumen of the gut- diarrhea and dehydration

Question 37

Pertussis toxin (hooping cough)

Answer 37

o Toxin covalently modifies αi subunit |  Prevents alpha subunit releasing GDP for GTP exchange