Part of the WAVE1 complex that regulates actin filament reorganization via its interaction with the Arp2/3 complex (By similarity). Involved in T-cell adhesion and p53-dependent induction of apoptosis (By similarity). Does not bind RNA. As component of the WAVE1 complex, required for BDNF-NTRK2 endocytic trafficking and signaling from early endosomes (PubMed:27605705). Component of the WAVE1 complex composed of ABI2, CYFIP1 or CYFIP2, BRK1, NCKAP1 and WASF1/WAVE1. Interacts with FMR1, FXR1 and FXR2 (PubMed:11438699). Interacts with FMR1; the interaction occurs in a RNA-dependent manner (By similarity). Interacts with RAC1 (activated form) which causes the complex to dissociate, releasing activated WASF1 (By similarity). The complex can also be activated by NCK1 (By similarity). Interacts with SHANK3; the interaction mediates the association of SHANK3 with the WAVE1 complex (PubMed:24153177). Interacts with TMEM108 (via N-terminus); the interaction associates TMEM108 with the WAVE1 complex (PubMed:27605705). Highly expressed in the perinuclear region and enriched in synaptosomes (PubMed:11438699). Expressed in hippocampus (at protein level). Partially edited. Editing appears to be brain-specific. Belongs to the CYFIP family. Extended N-terminus.