Membrane lecture 8 Flashcards
1
Q
Signalling overview
A
- Signal binds 7TM, GPCR binds G protein + activates → a+B subunits
- 800 GPCRs
- ↑ range of responses
- Important drug target
2
Q
Classification
A
- homology (Classes, classA = largest, rhodopsin-like, classC = metabotropic glutamate)
- Graf system
- Genetic structure (1st no = what helix residue of interest is on)
3
Q
Rhodopsin
A
- 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,
4
Q
Dynamics
A
- Dynamic so ↑ conformational heterogeneity, hard to crystallise
- Basal activity at low concentration of drug
5
Q
Non-rhodopsin structure
A
- B2 -adrenergic receptor
- Removed long flexible loop 3, lipid cubic phase
6
Q
Key differences btw different states
A
- Ionic lock (DRY/ERY at iC of TM3, salt bridge to E6/40 in inactive state)
- Breaks upon activation
- NPxxY on TM4
- PIF motif
7
Q
Activation
A
- 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
8
Q
Arrestin
A
- 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