Question

Which of the following can act as GAPs for heterotrimeric GTPases ? A. The GPCR. B. RGS only. C. The target of the alpha subunit of the GTPase only. D. The beta-gamma subunits of the GTPase. E. The target of the alpha subunit of the GTPase or a RGS.

Answer 1

ANSWER is : E. The target of the alpha subunit of the GTPase or a RGS.

EXPLANATION :

Heterotrimeric G protein activity is regulated by the binding and hydrolysis of GTP by the alpha subunit. Alpha subunits have intrinsic GTPase activity so bound GTP is hydrolyzed to GDP

Most GAPs that act on alpha subunits of heterotrimeric G proteins us belonged to regulators of G protein signaling (or RGS) protein family.

RGS are protein structural domains that can activate GTPases for heterotrimeric G-protein alpha- subunits.
G- protein alpha subunits has intrinsic GTPase activity that become inactivated after acting on their targets, that process is regulated by RGS.