Part of the WAVE complex that regulates lamellipodia formation. The WAVE complex regulates actin filament reorganization via its interaction with the Arp2/3 complex. Actin remodeling activity is regulated by RAC1. As component of the WAVE1 complex, required for BDNF-NTRK2 endocytic trafficking and signaling from early endosomes. Component of the WAVE1 complex composed of ABI2, CYFIP1 or CYFIP2, BRK1, NCKAP1 and WASF1/WAVE1. Within the complex, a heterodimer containing NCKAP1 and CYFIP1 interacts with a heterotrimer formed by WAVE1, ABI2 and BRK1. Component of the WAVE2 complex composed of ABI1, CYFIP1/SRA1, NCKAP1/NAP1 and WASF2/WAVE2. CYFIP2 binds to activated RAC1 which causes the complex to dissociate, releasing activated WASF1. The complex can also be activated by NCK1. Associates preferentially with the first SH3 domain of NCK. Interacts with NYAP1, NYAP2 and MYO16 (By similarity). (Microbial infection) Interacts with human cytomegalovirus protein UL135. At the interface between the lamellipodial actin meshwork and the membrane. Expressed in all tissues examined except peripheral blood leukocytes, with highest expression in brain, heart, and skeletal muscle. Expressed in cells of various brain regions including Purkinje cells and dentate nucleus of the cerebellum, CA4 region and dentate gyrus of the hippocampus, and in frontal gray and white matter (PubMed:28940097). Belongs to the HEM-1/HEM-2 family. Extended N-terminus.