Correct option is B
GTPase activating proteins (GAPs) play a crucial role in the regulation of heterotrimeric G proteins by inactivating the Gα subunit.
Heterotrimeric G proteins consist of three subunits: Gα, Gβ, and Gγ. The Gα subunit binds GTP and is active when GTP is bound, while it is inactive when GDP is bound. The activation of G proteins occurs when a G-protein coupled receptor (GPCR) is activated by a ligand, leading to the exchange of GDP for GTP on the Gα subunit.
GTPase Activating Proteins (GAPs): GAPs are responsible for accelerating the hydrolysis of GTP to GDP on the Gα subunit. This GTP hydrolysis inactivates the Gα subunit, causing it to dissociate from the Gβ/Gγ dimer and returning the G protein to its inactive state. By stimulating GTP hydrolysis, GAPs effectively turn off Gα's activity.
Therefore, the function of GAPs is to inactivate Gα protein by promoting the hydrolysis of GTP to GDP, which leads to the termination of the signaling event initiated by the activated G protein.
Information Booster:
GTPase Activation and Signaling Regulation: In the active form, Gα is bound to GTP, and it can interact with and activate downstream effector proteins. After GAP-mediated GTP hydrolysis, the Gα subunit switches to its inactive form, GDP-bound, and dissociates from the effector and the Gβ/Gγ subunits. This resets the G protein signaling system.
Role of GAPs: GAPs are critical for ensuring that the signaling event does not persist longer than necessary. By accelerating GTP hydrolysis, GAPs effectively turn off the signal and allow for the proper regulation of cell responses to external stimuli.
