Amino acid substitution in α‐helix 7 of Cry1Ac δ‐endotoxin of Bacillus thuringiensis leads to enhanced toxicity to Helicoverpa armigera Hubner

Publisher Website
Google Scholar
Abstract
Insecticidal proteins or δ-endotoxins of Bacillus thuringiensis are highly toxic to a wide range of agronomically important pests. The toxins are formed of three structural domains. The N-terminal domain is a bundle of eight α-helices and is implicated in pore formation in insect midgut epithelial membranes. All the δ-endotoxins share a common hydrophobic motif of eight amino acids in α-helix 7. A similar motif is also present in fragment B of diphtheria toxin (DT). Site-directed mutagenesis of Cry1Ac δ-endotoxin of B. thuringiensis was carried out to substitute its hydrophobic motif with that of DT fragment B. The mutant toxin was shown to be more toxic to the larvae of Helicoverpa armigera (cotton bollworm) than the wild-type toxin. Voltage clamp analysis with planar lipid bilayers revealed that the mutant toxin opens larger ion channels and induces higher levels of conductance than the wild-type toxin.