FIG 6.

Proposed mode of action of the binary Vip1/Vip2 toxin. The Vip1 protoxin is proteolytically processed by midgut proteases. The activated toxin binds to specific receptors either as a monomeric form or after oligomerization. Vip2 then binds to the oligomeric Vip1 protein and enters the cell either by endocytosis of the whole complex or directly through the pore formed by Vip1. Once inside the cytosol, Vip2 catalyzes the transfer of the ADP-ribose group from NAD to the actin monomers, preventing their polymerization.