Protein transport. Probably involved in vesicular traffic (By similarity). Interacts with RIMS2, RPH3A and RPH3AL (By similarity). Interacts with RIMS1 (PubMed:9252191). Interacts with GDI2 and CHM; phosphorylation at Thr-86 disrupts these interactions (By similarity). Interacts with MADD (via uDENN domain); the GTP-bound form is preferred for interaction (By similarity). Phosphorylation of Thr-86 in the switch II region by LRRK2 prevents the association of RAB regulatory proteins, including CHM and RAB GDP dissociation inhibitor GDI2. Belongs to the small GTPase superfamily. Rab family.