The Wiskott-Aldrich Syndrome Protein (WASp) is a 502-amino acid protein that is expressed in cells of the hematopoietic system. In the inactive state, WASp exists in an auto-inhibited conformation with sequences near its C-terminus binding to a region near its N-terminus. Its activation is dependent upon Cdc42 and PIP2 acting to disrupt this interaction causing the WASp protein to 'open'.

This exposes a domain near the WASp C-Terminus that binds to and activates the Arp2/3 complex. Activated Arp2/3 nucleates new F-actin. WASp is the founding member of a gene family which also includes the broadly expressed N-WASP (neuronal Wiskott-Aldrich Syndrome protein), and Scar.