The function of ENSG00000100359 (SGSM3, small G protein signaling modulator 3) is as follows. GTPase-activating protein (GAP) specific for Rab5 small GTPase for which it accelerates the intrinsic GTP hydrolysis rate, thereby controlling trafficking through the early endocytic pathway (PubMed:16086013, PubMed:17562788). May play a cooperative role in NF2- mediated growth suppression of cells. {ECO:0000269|PubMed:15541357, ECO:0000269|PubMed:16086013, ECO:0000269|PubMed:17562788}.