GTPase activating protein (GAP) which specifically converts GTP-bound Rho-type GTPases including RAC1 and CDC42 in their inactive GDP-bound form. By specifically inactivating RAC1 at the leading edge of migrating cells, it regulates the spatiotemporal organization of cell protrusions which is important for proper cell migration (PubMed:21658605). Also negatively regulates CDC42 in the process of actin remodeling and the formation of epithelial cell junctions (PubMed:22891260). Through its GAP activity toward RAC1 and/or CDC42 plays a specific role in phagocytosis of large particles. Specifically recruited by a PI3 kinase/PI3K-dependent mechanism to sites of large particles engagement, inactivates RAC1 and/or CDC42 allowing the reorganization of the underlying actin cytoskeleton required for engulfment (PubMed:26465210). It also plays a role in angiogenesis and the process of repulsive guidance as part of a semaphorin-plexin signaling pathway. Following the binding of PLXND1 to extracellular SEMA3E it dissociates from PLXND1 and inactivates RAC1, inducing the intracellular reorganization of the actin cytoskeleton and the collapse of cells (PubMed:24841563). Interacts with RAC1 (By similarity). Interacts with the exocyst via EXOC4 and EXOC8; required for the localization of both SH3BP1 and the exocyst to the leading edge of migrating cells (PubMed:21658605). Interacts with CD2AP and CGNL1; probably part of a complex at cell junctions (PubMed:22891260). Interacts with CAPZA1; recruits CAPZA1 to forming cell junctions (PubMed:22891260). May interact with AFDN (PubMed:22891260). Interacts with PLXND1; they dissociate upon SEMA3E binding to PLXND1 allowing SH3BP1 to transduce downstream signal through RAC1 inactivation (PubMed:24841563). Interacts with ABL1, GRB2 and SRC (via SH3 domain) (By similarity). Localizes at the leading edge of migrating cells (PubMed:21658605, PubMed:24841563). Accumulation at forming phagocytic cups is PI3 kinase/PI3K-dependent and is specific for sites of large particles engagement and their phosphatidylinositol 3,4,5-triphosphate membrane content (PubMed:26465210). The BAR domain mediates interaction with the exocyst components EXOC4 and EXOC8 and is required for the function in cell migration (PubMed:21658605). It also mediates the interaction with PLXND1 (PubMed:24841563). Truncated N-terminus. Truncated N-terminus. Truncated C-terminus.