Question

Adenylyl cyclase and PI-PLCb are_________

Which of the following answers is incorrect?

both activated by the trimeric G protein-alpha subunit binding to GDP.

both inactivated when trimeric G protein-alpha subunit is hydrolyzing the GTP to GDP.

both effectors in GPCRs’ signaling pathways

both activated by the activated trimeric G protein-alpha subunit.

both produce secondary messengers when activated by the trimeric G protein-alpha subunit.

Answer 1

Adenylyl cyclase is an enzyme which catalyzes the conversion ofd ATP to cAMP with its subsequent hydrolysis to 5'-AMP by Phosphodiesterase. PI-PLCb is phosphoinositide-specific phospholipase Cb which acts as effector along with takes placeadenylyl cyclase in G-protein coupled receptors (GPCRs) signaling pathway. Activation of G-protein takes place when any ligand binds with GPCRs. G protein in turn will interact with effector proteins like adenylyl cyclase and PI-PLCb which result in desired effect.

The inactive G-protein is atrimer with alpha, beta and gamma subunits. When activated, GTP binds and the beta-gamma subunits dissociate from the alpha subunit. Both adenylyl cyclase and PI-PLCb are activated by the trimeric G-protein-alpha subunit binding to GTP (G-alpha-GTP).

The active G-alpha-GTP is inactivated by GTPase of the alpha subunit when GTP is hydrolyzed to GDP. So both adenylyl cyclase and PI-PLCb are inactivated when trimeric G protein-alpha subunit is hydrolyzing the GTP to GDP.

The binding of any ligand to GPCRs triggers a configurational change in the G protein which induces the release of bound GDP and allows GTP to bind. So with the formation of G-alpha-GTP, it activates both adenylyl cyclase and PI-PLCb.

Both adenylyl cyclase and PI-PLCb produce secondary messengers like cAMP when activated by the trimeric G protein-alpha subunit. cAMP is produced in the cell in response to activation of adenylyl cyclase by active G protein.

So the incorrect statement is (a)