GPCR Flashcards
What is an agonist?
Bind to receptor and activates it - leads to signal transduction
What is an antagonist?
Bind to receptor and block activity (block normal ligand binding/signal transduction)
What are some examples of the wide range of stimuli for GPCR
Sensory GPCR - light, odour, taste Ions - H+, Ca2+ Neurotransmitters - Ach, glutamate Hormones - glucagon, adrenaline Large glycoproteins - thyroid stimulating hormone
What is the common structure of GPCR?
Single polypeptide chain that contains 7 transmembrane spanning domains with an extracellular N and intracellular C termini.
Activated GPCR can interact with G protein, causing …
Following conformational change, GDP is exchange for GTP in the alpha subunit of the G protein - active. The alpha subunit then dissociated got the beta-gamma complex, and can interact eight an effector protein
What is a G protein?
A guanine nucleotide binding protein.
Heterotrimeric
What happens to terminate G protein signalling?
The alpha subunit contains intrinsic GTPase activity that hydrolyses GTP back to GDP (releasing Pi). Alpha (GDP) subunit and beta-gamma complex then reform the inactive heterotrimeric G protein
What are adrenoceptors and how many subtypes are there?
GPCRs that bind adrenaline/noradrenaline
There are two main groups of adrenergic receptors, α and β, with several subtypes.
There are alpha 1, alpha 2 and beta adrenoreceptors.
Alpha 1 is a Gq coupled receptor
Alpha 2 is a Gi coupled receptor
β receptors (subtypes β1, β2 and β3)are Gs receptors
What is the effect of adrenaline/noradrenaline on beta adrenoreceptors?
Activates adenylyl cyclase
What is the effect of adrenaline/noradrenaline on alpha 1 adrenoreceptors?
Activates phospholipase C
What is the effect of adrenaline/noradrenaline on alpha 2 adrenoreceptors?
Inhibits adenylyl cyclase
What are muscarinic receptors and what type of GPCR are they?
GPCRs that bind acetyl Choline. 4 main types
M2/M4 are Gi receptors
M1/M3 are Gq receptors
What is the effect of acetyl choline on M1/M3 muscarinic receptors?
Activates phospholipase C
What is the effect of acetyl choline on M2/M4 muscarinic receptors?
Inhibits adenylyl cyclase
How does cholera toxin (CTx) affect GPCRs?
CTx prevents the alpha subunits GTPase activity therefore the signal is overactive - cannot be turned off
How does pertussis toxin (PTx) affect GPCRs?
PTx prevents GDP to GTP activation the the alpha subunit of Gi receptors therefore the GPCR pathway cannot be activated to transduce signals
What are the two main categories of GPCR effectors?
Enzymes - e.g. adenylyl cyclase or phospholipase C
Ion channels - e.g. Voltage gated Ca2+ channels (VGCC)
What is adenylyl cyclase stimulated by?
Gs receptor pathway
What are the examples of Gs receptors?
Beta adrenoreceptors
D1 dopamine receptors
H2 histamine receptors
What is adenylyl cyclase inhibited by?
Gi receptor pathway
What does adenylyl cyclase catalyse?
The conversion of ATP to cAMP
Give three examples of Gi receptors
Alpha 2 adrenoceptors
D2 dopamine receptors
Gamma-opioid receptors
How many subunits does protein kinase A (PKA) have?
2 catalytic subunits
2 regulatory subunits (where cAMP binds)
What does cAMP binding to PKA trigger?
Causes release of catalytic subunits which are then available to phosphorylate target proteins in the cells