Protein transport. Probably involved in vesicular traffic (By similarity). Interacts with RIMS1, RIMS2, RPH3A and RPH3AL. The GTP-bound form interacts with GAS8/DRC4 (via coiled-coil domains) (By similarity). Interacts with GDI2, CHM and CHML; phosphorylation at Thr-86 disrupts these interactions (PubMed:29125462). Interacts with MADD (via uDENN domain); the GTP-bound form is preferred for interaction (By similarity). Colocalizes with GAS8/DRC4 in the Golgi apparatus. Phosphorylation of Thr-86 in the switch II region by LRRK2 prevents the association of RAB regulatory proteins, including CHM, CHML and RAB GDP dissociation inhibitor GDI2. Belongs to the small GTPase superfamily. Rab family.