Functional characterization of multidomain protein Vip3Aa from Bacillus thuringiensis reveals a strategy to increase its insecticidal potency

Microbially derived, protein-based biopesticides offer a more sustainable pest management alternative to synthetic pesticides. Vegetative insecticidal proteins (Vip3), multidomain proteins secreted by Bacillus thuringiensis, represent a second-generation insecticidal toxin that have been used in transgenic crops. However, the molecular mechanism underlying Vip3s toxicity is poorly understood. Here, we determine the distinct functions and contributions of the domains of the Vip3Aa protein to its toxicity against Spodoptera frugiperda larvae. Vip3Aa domains II and III (DII-DIII) bind the midgut epithelium, while DI maintains the tetrameric state of the Vip3Aa protoxin, which is essential for its stability and toxicity. DI-DIII can be activated by midgut proteases, and exhibits ex vivo cytotoxicity similar to full-length Vip3Aa. We also determine that DV binds the peritrophic matrix via its glycan-binding activity, which is essential for Vip3Aa insecticidal activity. We further show that Vip3Aa has multiple protease activation sites and that introducing additional cleavage sites between DI and DII can increase the proteolysis efficiency and boost Vip3Aa insecticidal potency. This study provides insights into Vip3Aas mode-of-action and demonstrates a proof-of-concept strategy to enhance the insecticidal potency of Vip3Aa, which should significantly improve its application and development as a biopesticide.