Involved in the transport of proteins between the endosomes and the trans Golgi network. Interacts (GTP-bound form) with SGSM1; the GDP-bound form has much lower affinity for SGSM1 (PubMed:25220469). The GTP-bound form but not the GDP-bound form interacts with HPS4 and the BLOC-3 complex (heterodimer of HPS1 and HPS4) but does not interact with HPS1 alone (By similarity). Recruited to phagosomes containing S.aureus or Mycobacterium. Belongs to the small GTPase superfamily. Rab family.