Small GTPase which cycles between an active GTP-bound and an inactive GDP-bound state (By similarity). Involved in protein transport. Plays a role in vesicular traffic. Mediates VEGFR2 endosomal trafficking to enhance VEGFR2 signaling (By similarity). Acts as a regulator of platelet alpha-granule release during activation and aggregation of platelets (By similarity). GTP + H2O = GDP + H(+) + phosphate Interacts with SGSM1, SGSM2 and SGSM3 (By similarity). Interacts with RAB11FIP1, RABEP1, ZFYVE20 and RUFY1. Interacts (membrane-bound form) with NDRG1; the interaction involves NDRG1 in vesicular recycling of E-cadherin. Interacts (in GTP-bound form) with GRIPAP1 (via N-terminus) (PubMed:20098723). Interacts with RABEP1 and RBSN (By similarity). Does not interact with HPS4 (By similarity). Interacts with RABEP2; this interaction may mediate VEGFR2 cell surface expression (By similarity). Generally associated with membranes. Cytoplasmic when phosphorylated by CDK1. Serotonylation of Gln-72 by TGM2 during activation and aggregation of platelets leads to constitutive activation of GTPase activity. Phosphorylated by CDK1 kinase during mitosis. Belongs to the small GTPase superfamily. Rab family.