Direct binding of the verprolin-homology domain in N-WASP to actin is essential for cytoskeletal reorganization.

Verprolin is a yeast protein whose inactivation leads to a cytoskeletal defect characterized by the abnormal organization of actin filaments. Recently, two mammalian proteins previously shown to regulate the actin cytoskeleton, Wiskott-Aldrich Syndrome Protein (WASP) and its homolog expressed in neurons (N-WASP), were found to possess short peptide motifs homologous to one part of verprolin. However, the physiological function of the homologous regions (verprolin-homology domain, VPH domain) remains unknown. Here we report the importance of the VPH domain as the direct actin binding region. In the case of N-WASP, the VPH domain co-acts with the cofilinhomologous region to sever actin filaments in vitro. Furthermore, the VPH domain is indispensable for the reorganization of the actin cytoskeleton by N-WASP downstream of tyrosine kinases in living cells. All data demonstrate that the VPH domain plays critical roles in the regulation of the actin cytoskeleton.