Implicated in endocytosis. Involved ultrafast endocytosis, by mediating, in a first step, neck formation and in a second step, aids in the removal of clathrin coats from the regenerated vesicles. May recruit other proteins to membranes with high curvature. Required for BDNF-dependent dendrite outgrowth. Cooperates with SH3GL2 to mediate BDNF-NTRK2 early endocytic trafficking and signaling from early endosomes. . This is the function of SH3GL2 (SH3 domain containing GRB2 like 2, endophilin A1, ENSG00000107295).