Protein transport. Probably involved in vesicular traffic (By similarity). Interacts with RIMS1, RIMS2, RPH3A and RPH3AL (By similarity). Interacts with GDI2, CHM and CHML; phosphorylation at Thr-94 disrupts these interactions (PubMed:29125462). Interacts with MADD (via uDENN domain); the GTP-bound form is preferred for interaction (By similarity). Expressed in brain, placenta and lung. Phosphorylation of Thr-94 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.