May be involved in melanosomal transport and docking. Involved in the proper sorting of TYRP1. Involved in peripheral melanosomal distribution of TYRP1 in melanocytes; the function, which probably is implicating vesicle-trafficking, includes cooperation with ANKRD27 and VAMP7 (By similarity). Plays a role in the maturation of phagosomes that engulf pathogens, such as S.aureus and M.tuberculosis (PubMed:21255211). Plays an important role in the control of melanin production and melanosome biogenesis (PubMed:23084991). In concert with RAB32, regulates the proper trafficking of melanogenic enzymes TYR, TYRP1 and DCT/TYRP2 to melanosomes in melanocytes (By similarity). Regulated by a guanine nucleotide-exchange factor (GEF) and a GTPase-activating protein (GAP) and alternates between an inactive GDP-bound and an active GTP-bound form. The BLOC-3 complex composed of HPS1 and HPS4 acts as its GEF, promotes the exchange of GDP to GTP, converting it from an inactive GDP-bound form into an active GTP-bound form. SGSM2 acts as its GAP and inactivates it by stimulating its GTPase activity. Interacts with ANKRD27 (PubMed:19403694). Recruited to phagosomes containing S.aureus or M.tuberculosis (PubMed:21255211). The BLOC-3 complex, a heterodimer of HPS1 and HPS4 promotes its membrane localization (PubMed:23084991). Expressed in melanocytes. Although at least one in vitro system can process and methylate the prenylated C-terminal, in an in vitro system that normally express Rab-38 and in vivo the prenylated C-terminal is not proteolytically processed and not methylated. Belongs to the small GTPase superfamily. Rab family.