G proteins

Question 1

Structure

Answer 1

• 7 transmembrane bundle consisting of 7-a- helices with an extracellular N terminus of varying length
• intracellular C terminus

Question 2

Classes

Answer 2

• secretin (class b)
• glutamate-like (class c)
• frizzled
• rhodopsin-like (class a)
• adhesion (class b)

Question 3

Rhodopsin family

Answer 3

• odourant receptors

- other endogenous ligands include amine neurotransmitters ( adrenaline, 5HT, cannabinoids)

Question 4

Secretin like family

Answer 4

• characterised by a conserved N-terminal domain comprising -120 AA’s with 2 conserved disulphide bridges
• bind peptides
• endogenous peptides bind via a two domain interaction with the N-terminus of the receptor acting with the C terminus of the peptide and the n terminus of the peptide interacting with the 7-TM bundle

Question 5

Glutamate like family

Answer 5

• obligate dimers
• very large extracellular domain that forms a characteristic tertiary structure resembling a venus fly trap which binds the endogenous ligand

Question 6

G proteins

Answer 6

• Inactive state, conjugated with GDP
• active state, conjugated with GTP
• equilibrium pushed to active state by high GTP concentration and high affinity for GTP over GDP
• transition assisted by GEF

Question 7

Gai/o

Answer 7

a: inhibits adenylate cyclase activity -> lowers PKA & EPAC activity
Bgamma: activates K+ channels, inhibits Ca2+ channels -> changes membrane potential

Question 8

Gas

Answer 8

a: potentiates adenylate cyclase activity -> changes membrane potential

Question 9

Gaq/11

Answer 9

a: potentates phospholipase C-B activity -> activates IP3 receptors and protein kinase C

Question 10

Ga 12/113

Answer 10

a: activates Rho GEF -> Activates Rho…ROCK