Membrane lecture 8

Question 1

Signalling overview

Answer 1

• Signal binds 7TM, GPCR binds G protein + activates → a+B subunits
• 800 GPCRs
• ↑ range of responses
• Important drug target

Question 2

Classification

Answer 2

1. homology (Classes, classA = largest, rhodopsin-like, classC = metabotropic glutamate)
2. Graf system
3. Genetic structure (1st no = what helix residue of interest is on)

Question 3

Rhodopsin

Answer 3

• Found in rod cells
• 2 glycosylation sites at NTD, N-2/15
• 2 palmitoylation sites at C
• Lys 296
• Glycosylation on inside disc
• Conversion of light (light causes retinal to isomerase, lys → trans, 1 rhodopsin activates 100 transducers, CGMP hydrolysed, allows Na+ to open,

Question 4

Dynamics

Answer 4

• Dynamic so ↑ conformational heterogeneity, hard to crystallise
• Basal activity at low concentration of drug

Question 5

Non-rhodopsin structure

Answer 5

• B2 -adrenergic receptor

- Removed long flexible loop 3, lipid cubic phase

Question 6

Key differences btw different states

Answer 6

• Ionic lock (DRY/ERY at iC of TM3, salt bridge to E6/40 in inactive state)
• Breaks upon activation
• NPxxY on TM4
• PIF motif

Question 7

Activation

Answer 7

• Lock opens, outward movement of TM5+6
• Mutant E113Q, TM5/6 move away
• Resting → intermediate state
• Ionic lock x always broken
• NPxxY conserved
• Pif has subtle movement

Question 8

Arrestin

Answer 8

• Ligand induced conf change in GPCR facilitates interaction w/ G protein
• GPCR = GEF for Ga
• Second messengers = activated by effectors
• B-arresting binds to phosph GPCR
• Cells become desensitised
• Agonist can bind and activate state that would be phosphorylated → arresting bound