Cry11Aa toxin from Bacillus thuringiensis binds its receptor in Aedes aegypti mosquito larvae through loop α-8 of domain II

Bacillus thuringiensis subs israelensis produces Cry toxins active against mosquitoes. Receptor binding is a key determinant for specificity of Cry toxins composed of three domains. We found that exposed loop α-8 of Cry11Aa toxin, located in domain II, is an important epitope involved in receptor interaction. Synthetic peptides corresponding to exposed regions in domain II (loop α-8, β-4 and loop 3) competed binding of Cry11Aa to membrane vesicles from Aedes aegypti midgut microvilli. The role of loop α-8 of Cry11A in receptor interaction was demonstrated by phage display and site-directed mutagenesis. We isolated a peptide-displaying phage (P5.tox), that recognizes loop α-8 in Cry11Aa, interferes interaction with the midgut receptor and attenuates toxicity in bioassay. Loop α-8 mutants affected in toxicity and receptor binding were characterized.