Involved in regulation of actin and microtubule organization. Part of a WAVE complex that activates the Arp2/3 complex (By similarity). As component of the WAVE1 complex, required for BDNF-NTRK2 endocytic trafficking and signaling from early endosomes (PubMed:27605705). Homotrimer when in free form. Directly interacts with WASF2. 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 (By similarity). Belongs to the BRK1 family.