What is the function of the GTPase activity in G proteins?
The GTPase stimulates GDP to GTP exchange to activate signaling.
The GTPase cleaves GTP to generate GDP and inactivate signaling.
The GTPase cleaves GTP to generate GDP and activate signaling.
The GTPase synthesize cyclic GMP to regulate downstream signals.
The correct answer and explanation is :
The correct answer is:
The GTPase cleaves GTP to generate GDP and inactivate signaling.
Explanation:
G proteins (guanine nucleotide-binding proteins) are critical components in cell signaling pathways, serving as molecular switches that regulate various physiological processes. The activity of G proteins is controlled by their ability to bind and hydrolyze guanosine triphosphate (GTP). These G proteins can exist in two states: an “active” GTP-bound state and an “inactive” GDP-bound state.
The key function of the GTPase activity in G proteins is to hydrolyze GTP to GDP. This process involves the enzymatic cleavage of the phosphate group from GTP, which results in the formation of GDP. This hydrolysis event is essential for inactivating the signaling pathway that is activated by the GTP-bound state.
- Active State (GTP-bound): When G proteins bind GTP, they are in an active state. In this state, they can interact with downstream effectors (such as adenylyl cyclase or phospholipase C) and trigger cellular responses, such as changes in cyclic AMP levels or the release of intracellular calcium.
- Inactive State (GDP-bound): The GTPase activity of the G protein cleaves GTP to GDP, causing the protein to shift into an inactive conformation. In this state, the G protein is unable to interact with downstream effectors, thereby terminating the signaling process.
This hydrolysis of GTP to GDP is a crucial mechanism for spatial and temporal regulation of signaling. It ensures that the signaling pathways are turned off once the necessary response has been achieved, preventing prolonged or inappropriate signaling. The exchange of GDP for GTP (a separate process) reactivates the G protein, allowing it to signal again.
Thus, the GTPase activity of G proteins serves as a critical control point in regulating cellular signaling, ensuring proper activation and deactivation of signaling pathways.