GPCR vs enzyme-linked receptors Flashcards
lecture 14
What was the first function discovered for G proteins?
Activating adenylyl cyclase through the α subunit
What are the two primary G protein subunits involved in regulating adenylyl cyclase?
αs: stimulates AC
αi: inhibits AC
Name four receptors that couple to Gs proteins.
β-adrenoceptors, vasopressin receptors, A2A adenosine receptors, and AB adenosine receptors.
Name four receptors that couple to Gi proteins.
α2-adrenoceptors, μ and δ opioid receptors, A1/3 adenosine receptors.
What class of G proteins activates phospholipase C (PLC)?
Gq proteins.
Name two key functions of Gq proteins.
Activating PLC and increasing intracellular Ca²⁺ levels.
How does cholera toxin (CTx) affect G protein signalling?
It ADP-ribosylates the as subunit, preventing GTP hydrolysis ad causing persistent activation.
What is the consequences of persistent activation of as in the colon?
Activation of PKA-dependent Cl- channels, leading to secretory diarrhoea.
How does pertussis toxin (PTx) affect G protein signalling?
It locks the ai subunit in an inactive state, preventing inhibitory control over AC/PKA.
What condition is associated with pertussis toxin’s action?
Whooping cough, due to increased cAMP and PKA activity in airways.
What does PLC cleave, and what are the products?
PLC cleaves PIP2 into IP3 in DAG.
What is the function of IP3 in Gq signalling?
It stimulates Ca2+ release from the endoplasmic reticulum.
What is the role of DAG in Gq signalling?
It recruits and activates protein kinase C (PKC) at the membrane.
How does PKC influence cellular response?
PKC phosphorylates proteins, potentiates IP3 effects, and regulates cell shape, proliferation, and transcription.
What protein binds Ca2+ to mediate intracellular responses?
Calmodulin (CaM), which binds 4 Ca2+ ions.
