A chemical inhibitor of N-WASP reveals a new mechanism for targeting protein interactions

Cell morphology and motility are governed largely by complex signaling netw orks that ultimately engage the actin cytoskeleton. Understanding how indiv idual circuits contribute to the process of forming cellular structures wou ld be aided greatly by the availability of specific chemical inhibitors. We have used a novel chemical screen in Xenopus cell-free extracts to identif y compounds that inhibit signaling pathways regulating actin polymerization . Here we report the results of a high-throughput screen for compounds that inhibit phosphatidylinositol 4,5-bisphosphate (PIP2-induced actin assembly and the identification of the first compound, a cyclic peptide, known to b lock actin assembly by inhibiting an upstream signaling component. We ident ify the target of this compound as N-WASP, a protein that has been investig ated for its role as a node interconnecting various actin signaling network s. We show that this compound prevents activation of the Arp2/3 complex by N-WASP by allosterically stabilizing the autoinhibited conformation of N-WA SP.