Neural Wiskott-Aldrich syndrome protein (N-WASP) is the specific ligand for Shigella VirG among the WASP family and determines the host cell type allowing actin-based spreading

Shigella, the causative agent of bacillary dysentery, is capable of directing its movement within host cells by forming an actin comet tail. The VirG (IcsA) protein expressed at one pole of the bacterium recruits neural Wiskott-Aldrich syndrome protein (N-WASP), a member of the WASP family, which in turn stimulates actin-related protein (Arp) 2/3 complex-mediated actin polymerization. As all the WASP family proteins induce actin polymerization by recruiting Arp2/3 complex, we investigated their involvement in Shigella motility. Here, we show that VirG binds to N-WASP but not to the other WASP family proteins. Using a series of chimeras obtained by swapping N-WASP and WASP domains, we demonstrated that the specificity of VirG to interact with N-WASP lies in the N-terminal region containing the pleckstrin homology (PH) domain and calmodulin-binding IQ motif of N-WASP. A conformational change in N-WASP was important for the VirG-N-WASP interaction, as elimination of the C-terminal acidic region, which is responsible for the intramolecular interaction with the central basic region of N-WASP, affected the specific binding to VirG. We observed that, in haematopoietic cells such as macrophages, polymorphonuclear leucocytes (PMNs) and platelets, WASP was predominantly expressed, whereas the expression of N-WASP was greatly suppressed. Indeed, unlike Listeria, Shigella was unable to move in macrophages at all, although the movement was restored as N-WASP was expressed ectopically. Thus, our findings demonstrate that N-WASP is a specific ligand of VirG, which determines the host cell type allowing actin-based spreading of Shigella.