Multiple regulatory pathways for N-WASP and WAVE2 activation. (a) N-WASP is autoinhibited in a basal state through the interaction between the GBD/CRIB domain and the VCA region. PIP2 and GTP-loaded Cdc42 bind to the B and GBD/CRIB domains, respectively, resulting in synergistic activation of N-WASP. Binding of SH3 domains to N-WASP can independently compete with the autoinhibitory interaction, and thus can activate N-WASP. SH3-domain-containing proteins that interact and potentially activate N-WASP include cortactin, WISH, Nck, Grb2, Crk, FBP17, CIP4, Toca1, Abi1, endophilin A, and sorting nexin 9 (not all shown on the diagram). Concurrently, the BAR-domain superfamily proteins bend the membrane. (b) WAVE proteins exist in cells as a heteropentameric protein complex as indicated. WAVE2 has been shown to translocate to the membrane via interactions with phosphatidylinositol-(3,4,5)-triphosphate (PIP3) and IRSp53. The affinity of WAVE2 for IRSp53 is enhanced when GTP-loaded Rac binds to the RCB/MIM domain of IRSp53. IRSp53 is also able to enhance the ability of WAVE2 to stimulate Arp2/3-mediated actin polymerization . This pathway via IRSp53 is an indirect activation by Rac, as it is suggested that Rac can activate the WAVE complex through direct interaction with Sra1. The direct pathway was shown in a recent paper but needs more experimental evidence to be widely accepted (hence marked by a question mark in the figure).