22. G-Protein Coupled Receptors Flashcards
How many times does a GPCR pass through the plasma membrane?
7
What are the 3 subunits of a g protein?
Alpha, beta, gamma
What is the main purpose of the alpha subunit?
Regulate amplifier or effector protein activity
What happens pre-activation?
The alpha and gamma subunits of the G-protein anchor it to the membrane in its inactive state (GDP bound)
What happens once a ligand binds to the GPCR?
Occupied receptor couples with the alpha subunit
GDP is replaced with GTP
What happens once the alpha subunit is activated?
Alpha complex dissociates from receptor to interact with the effector enzyme
Which alpha subunit activates adenylate cyclase?
Gas
What is the role of cAMP?
Activates protein kinases
These work in metabolic pathways and in ion channels
What is cAMP broken down by?
Phosphodiesterase
What does Gai do?
Inhibits adenylate cyclase
Inhibited by pertussis toxin (whooping cough)
How are GPCRs switched off?
GTP-ase activity of the alpha subunit is increased when the effector protein is bound
Causes hydrolysis of GTP to GDP
GDP-bound alpha subunit reunites with the beta-gamma complex
What can accelerate signalling of GPCRs?
Guanine-nucleotide Exchange Factors: GEF
ligand bound receptor
What can inhibit signalling to GPCRs?
Guanine-nucleotide Dissociation Inhibitor: GDI
beta-gamma complex
What turns off signalling of GPCRs?
GTP-ase Accelerating Proteins: GAP
What effect does the E.coli toxin have on adenylate cyclase activity?
Covalent modification of Gas so it can’t hydrolyse ATP
Elevated cAMP levels in colon cause severe diarrhea and dehydration
