Phosphorylation of the WASP-VCA domain increases its affinity for the Arp2/3 complex and enhances actin polymerization by WASP.

Wiskott-Aldrich syndrome protein (WASP) and neural (N)-WASP regulate dynamic actin structures through the ability of their VCA domains to bind to and stimulate the actin nucleating activity of the Arp2/3 complex. Here we identify two phosphorylation sites in the VCA domain of WASP at serines 483 and 484. S483 and S484 are substrates for casein kinase 2 in vitro and in vivo. Phosphorylation of these residues increases the affinity of the VCA domain for the Arp2/3 complex 7-fold and is required for efficient in vitro actin polymerization by the full-length WASP molecule. We propose that constitutive VCA domain phosphorylation is required for optimal stimulation of the Arp2/3 complex by WASP.