TSC2 (in the TSC complex) functions as a GTPase-activating protein and stimulates the intrinsic GTPase activity of the small G-protein Rheb. This results in the conversion of Rheb:GTP to Rheb:GDP. GDP-bound Rheb is unable to activate mTOR (Inoki et al. 2003, Tee et al. 2003). It is not demonstrated that RHEB hydrolyzes GTP when present in the mTORC1 complex; given the low affinity of RHEB for mTOR, it may dissociate from the mTORC1 complex before TSC2 stimulates hydrolysis of GTP; TSC2 may not have access to critical residues of RHEB when present inside mTORC1.