The Bright Side of Mutated G Protein: Increased Activity

What happens when the inhibitory Gα (Gia) protein is mutated and increases its intrinsic GTPase activity?

a. adenylate cyclase become more active
b. Gia becomes more active
c. Both
d. Neither

Answer:

When inhibitory Gα protein is mutated and increases its intrinsic GTPase activity, both adenylate cyclase and Gia become more active. The activity of Gia results in more efficient GTP hydrolysis. Option c is correct.

When the inhibitory Gα (Gia) protein undergoes a mutation that increases its intrinsic GTPase activity, both adenylate cyclase and Gia become more active. Gia is a heterotrimeric G protein that plays a crucial role in G protein-coupled receptor (GPCR) signaling pathways.

When a GPCR is activated by an extracellular ligand, Gia is released from the receptor and binds to GTP, becoming active and dissociating into its Gα-GTP and Gβγ subunits. The GTP-bound Gα subunit then triggers the inhibition of adenylate cyclase, leading to decreased production of cyclic AMP (cAMP).

However, in the case of a mutated Gia with increased GTPase activity, the Gα-GTP subunit is more efficient at hydrolyzing GTP to GDP, causing faster inactivation of Gia. As a result, the inhibitory effect on adenylate cyclase is diminished, allowing adenylate cyclase to become more active.

The increased adenylate cyclase activity leads to elevated levels of cAMP, which can initiate various downstream signaling cascades, ultimately influencing cellular responses. Therefore, both Gia and adenylate cyclase exhibit increased activity when the inhibitory Gα protein has a mutation that enhances its GTPase activity. Therefore, option c is correct, i.e., both.

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