Adapter protein that binds F-actin and DNM1, and thereby plays a role in receptor-mediated endocytosis. Plays a role in the reorganization of the actin cytoskeleton, formation of cell projections, such as neurites, in neuron morphogenesis and synapse formation via its interaction with WASL and COBL. Does not bind G-actin and promote actin polymerization by itself. Required for the formation of organized podosome rosettes. May act as a common effector of antigen receptor-signaling pathways in leukocytes. Acts as a key component of the immunological synapse that regulates T-cell activation by bridging TCRs and the actin cytoskeleton to gene activation and endocytic processes. Interacts with SHANK3, SYN1 and PRAM1 (By similarity). Interacts with SHANK2. Interacts with FGD1, DNM1 and MAP4K1. Interacts with ANKRD54. Interacts with COBL. Interacts with WASL and WIPF1. Associates with lamellipodial actin and membrane ruffles. Colocalizes with actin and cortactin at podosome dots and podosome rosettes. Detected in hippocampus neurons and in the Purkinje cell layer in cerebellum (at protein level). Predominantly expressed in brain, thymus and spleen. Also found in testis, heart and lung. Little or no expression detected in ovary or muscle. In the embryo, expression is high during early development but drops during later development. The SH3 domain mediates interaction with SHANK2, SHANK3 and PRAM1. Belongs to the ABP1 family.