Schematic representation of the GTPase cycle of small GTP-binding proteins. Small GTP-binding proteins cycle between an inactive GDP-bound state and an active GTP-bound state. GEFs facilitate the release of GDP, allowing small GTPases to bind to the abundant intracellular GTP and become activated. Activated small GTPases interact with effector proteins to transmit cellular signals. Due to their intrinsically low ability to hydrolyse GTP, small GTPases rely on GAPs to accelerate GTP hydrolysis, thereby reverting them to the inactive GDP-bound state.