GTPases are a large group of enzymes that catalyze hydrolysis of the γ phosphate bond in guanine triphosphate (GTP) to form guanine diphosphate (GDP). Mg2+ is essential for catalytic activity. GTPases have essential roles in signal transduction, protein synthesis and translocation, control of cell growth and differentiation and vesicular transport regulation.

There are six main families of GTPases; heterotrimeric G protein GTPases (E.C., small monomeric GTPases (E.C., protein-synthesizing (translational) GTPases (E.C., signal-recognition-particle GTPase (E.C., dynamin GTPases (E.C. and tubulin GTPases (E.C.