The pathogenesis of Shigella requires binding to the host protein N-WASP. To examine the roles of structural conformation and phospho-regulation of N-WASP during Shigello pathogenesis, mutant N-WASP constructs predicted to result in a constitutively open conformation (L229P and L232P) or either a phospho-mimicking (Y253E) or phospho-disruptive (Y253F) Structure were constructed. Pyrene actin assays demonstrated that the N-WASP L229P and L232P constructs are Constitutively active. Despite the increase in actin polymerization seen in vitro, cell lines expressing N-WASP L229P and L232P Supported shorter actin tails when infected with Shigella. Shigella actin tails were unchanged in cells expressing N-WASP phospho-regulation mutant proteins. Shigella invasion, intracellular, and intercellular motility were not altered in cells expressing N-WASP L229P or L232P. However, plaque numbers were increased in cells expressing N-WASP L229P and L232P. These data demonstrate that N-WASP Structural conformation is an important regulator of Shigella pathogenesis in distinct segments of its lifecycle. (C) 2009 Elsevier Inc. All rights reserved