Final answer:
A GTPase is an enzyme that converts GTP to GDP, regulating cell signaling. When RAS G-protein's GTPase activity is inhibited, it cannot hydrolyze GTP, causing continuous cell signaling and potential uncontrolled cell growth.
Step-by-step explanation:
A GTPase is an enzyme that hydrolyzes the guanosine triphosphate (GTP) to guanosine diphosphate (GDP), which is instrumental in cellular signaling and regulatory processes. The activity of a GTPase is usually controlled by GTPase-activating proteins (GAPs) that enhance the hydrolysis of GTP, and guanine nucleotide exchange factors (GEFs) that facilitate the exchange of GDP for GTP.
In certain cancers, when the GTPase activity of RAS G-protein is inhibited, RAS can no longer hydrolyze GTP to GDP, leading to continuous activation of the RAS G-protein. This persistent activation can result in unregulated cell growth, which may develop into cancer due to the constant stimulation of downstream cellular growth signals.
The control of GTPase activity is crucial as it forms part of a cycle where G-protein-linked receptors become activated upon ligand binding. Following activation, they release GDP, pick up GTP, and their subunits then separate, with one or both fragments capable of activating further cellular proteins. Eventually, hydrolysis of GTP back to GDP deactivates these subunits, reassociating them and thereby resetting the G-protein into its inactive form. This cycle is vital for regulating physiological processes such as vision, taste, and immune responses.