RAB proteins have intrinsic weak GTPase activity that is enhanced by RAB-GTPase activating proteins (RAB-GAPs, Sano et al. 2007). The GTPase activity of RAB13 is inferred from other RAB proteins. AS160 (TBC1D4) and TBC1D1 are GAPs that activate the GTPase activity of RAB8A/10/13. Insulin signaling activates AKT, which phosphorylates and inactivates AS160 and TBC1D1, allowing GTP-bound (active) RABs to accumulate.
As inferred from mouse, TBC1D1 activates GTPase activity of RAB2A, 8A, 8B, 10, and 14 (Roach et al. 2007).
The GAP domain of TBC1D4 (AS160) activates the GTPase activity of RAB proteins (Sano et al. 2007). The effect of TBC1D4 on RAB13 is inferred from rat muscle cells (Sun et al. 2010).