GTPase-activating protein (GAP) that stimulates the GTPase activity of Rho-type GTPases. Thereby, controls Rho-type GTPases cycling between their active GTP-bound and inactive GDP-bound states. Acts as a GAP at least for CDC42 and RAC1 (PubMed:25498153). In neurons, is involved in dendritic spine formation and synaptic plasticity in a specific RAC1-GAP activity (PubMed:25498153). Limits the initiation of exploratory dendritic filopodia. Recruited to actin-patches that seed filopodia, binds specifically to plasma membrane sections that are deformed inward by acto-myosin mediated contractile forces. Acts through GAP activity on RAC1 to reduce actin polymerization necessary for filopodia formation (PubMed:25498153). In association with SHANK3, promotes GRIA1 exocytosis from recycling endosomes and spine morphological changes associated to long-term potentiation (By similarity). Interacts with BST2 (via cytoplasmic domain). Interacts (probably via PDZ-binding motif) with SHANK3 (via PDZ domain); the interaction takes place in dendritic spines and promotes GRIA1 exocytosis (By similarity). In CA1 hippocampal synapses, detected at both presynaptic and postsynaptic sites (By similarity). Located in convoluted dendritic plasma membrane sections enriched in polymerized actin and myosin (patches) along dendrites where often emerge filopodia (PubMed:25498153). Expressed in brain, detected at high levels in hippocampal CA1 (at protein level). Expression increases in prefrontal cortex from 6 months to, at least, 39 months. Rho-GAP domain is required to promote GRIA1 exocytosis from recycling endosomes. Rho-GAP and BAR domains are necessary for the control of long-term potentiation in hippocampal neurons (By similarity). In dendrites, BAR domain mediates the recruitment to patches where plasma membrane is deformed by acto-myosin mediated contractile forces (PubMed:25498153). Contains a PDZ-binding motif at positions 767-770.