G Protein Coupled Receptors Flashcards
What are Metabophobic receptors?
They are indirectly linked to ion channels through signal transduction mechanisms such as G proteins.
What is the structure of GPCRs (G protein coupled receptors)?
- 7 TMs (alpha helices)
- TM3 is located near the binding site
- N terminus (extracellular) = ligand binding
- C terminus (intracellular) = G protein binding
What are protease-activated receptors in platelets?
N terminus is cleaved off of receptor which activates it.
How many independent stimuli activate platelets?
3
What are G proteins?
- belong to the GTPase family
- act as molecular switches to transmit signals from EC stimuli.
When are GPCRs active and not active?
When GTP is bound to the alpha subunit, it is ACTIVE.
GTP is hydrolysed to GDP and it is then INACTIVE.
How many families of G proteins exist?
6
What are effectors determined by?
The alpha subunit
What is the G protein mechanism?
- The ligand binds, which causes conformational changes and activated the G protein.
- GDP is released, alpha subunit binds to GTP and dis activated.
- Binds to target protein in membrane to elicit a response.
What controls the duration of signalling?
The rate of hydrolysis of GDP.
What do RGS proteins stimulate?
GTPase activity in the alpha subunit.
What is the half life of a G protein (t1/2)?
~15 seconds.
What can effectors be?
- Ion channels
- 2nd messenger systems
What are the effects of cholera?
- Stimulates alpha subunit
- Activates adenylate cyclase, cAMP, protein kinases
- increased Cl- ions, Na+, H20
- decreased electrolytes, diarrhoea, dehydration
What are the effects of whooping cough?
- Inhibits alpha subunit
- Inactivates inhibitory G protein
- Increase of cAMP
- Leads to erosion of respiratory epithelium
