WH2–actin interactions. (A) Actin is shown in the standard orientation with the subdomains labeled. The WH2 domain (blue) binds between subdomains 1 and 3 of monomeric actin (highlighted in green; PDB 3M1F). (B) In structural models of the actin filament (PDB 2ZWH shown here), the WH2 binding site is accessible at the barbed end of the filament but not the pointed end. (C) Based on the results of Burke et al. (2017), VopL/F is a dimer that nucleates new filaments from the pointed end. Shortly thereafter, the filament is released.