Q.38
A mutant Gα protein with increased GTPase activity would
Options:
(A) not bind to GTP
(B) not bind to GDP
(C) show increased signaling
(D) show decreased signaling
Increased GTPase activity in mutant Gα shortens the active GTP-bound state, reducing downstream signaling duration. This terminates GPCR-mediated signals faster than normal.
Correct Answer
Option (D) show decreased signaling is correct.
Gα activates effectors only when GTP-bound; faster hydrolysis to GDP inactivates it quicker, limiting signal output despite normal GTP binding. RGS proteins mimic this by accelerating GTPase, blunting responses.
G Protein Cycle Basics
Gα-GDP (inactive) exchanges to Gα-GTP (active) via GPCR-GEF action, dissociating βγ and effectors.
Intrinsic GTPase hydrolyzes GTP to GDP, reforming inactive heterotrimer; mutants or GAPs (RGS) speed this, shortening activation.
Thus, higher GTPase = briefer signaling pulses, not prolonged ones.
Option Breakdown
| Option | Claim | Correct? | Reason |
|---|---|---|---|
| (A) | not bind to GTP | No | GTPase affects hydrolysis, not binding; mutants retain GTP access |
| (B) | not bind to GDP | No | Faster hydrolysis increases GDP production; binding intact |
| (C) | show increased signaling | No | Opposite: quicker deactivation reduces active time |
| (D) | show decreased signaling | Yes | Shortened GTP state limits effector activation |
Exam Applications
Key concept: GTPase terminates signals; mutations increasing it (e.g., RGS mimic) desensitize pathways.
Contrast with constitutively active Q227L mutants (reduced GTPase = prolonged signaling).
Essential for signal transduction, pharmacology targeting GPCRs in biotech.
1 Comment
Ankita Pareek
April 18, 2026If g alfa is mutated show decreased signalling because increased gtpase activity convert active g alpha into inactive g alpha by converting gtp into gdp