The function of Ensembl gene identifier ENSG00000118873 (RAB3GAP2, RAB3 GTPase activating non-catalytic protein subunit 2) is as follows. Regulatory subunit of the Rab3 GTPase-activating (Rab3GAP) complex composed of RAB3GAP1 and RAB3GAP2, which accelerates the otherwise slow GTP hydrolysis catalyzed by Rab proteins (PubMed:9733780, PubMed:39779760). The complex has GTPase-activating protein (GAP) activity towards various Rab3 subfamily members (RAB3A, RAB3B, RAB3C and RAB3D), RAB5A and RAB43, and has guanine nucleotide exchange factor (GEF) activity towards RAB18 (PubMed:9733780, PubMed:39779760, PubMed:24891604). The Rab3GAP complex acts as a GEF for RAB18 by promoting GDP release from RAB18 and the conversion of inactive RAB18-GDP to the active form RAB18-GTP (PubMed:39779760, PubMed:24891604). Recruits and stabilizes RAB18 at the cis-Golgi membrane in human fibroblasts where RAB18 is most likely activated (PubMed:26063829). Also involved in RAB18 recruitment at the endoplasmic reticulum (ER) membrane where it maintains proper ER structure (PubMed:24891604). Required for normal eye and brain development (By similarity). May participate in neurodevelopmental processes such as cell proliferation, migration and differentiation before synapse formation, and non-synaptic vesicular release of neurotransmitters (By similarity). {ECO:0000250|UniProtKB:Q15042, ECO:0000269|PubMed:24891604, ECO:0000269|PubMed:26063829, ECO:0000269|PubMed:9733780}.