61.
Background
Bacillus thuringiensis Cry1Aa insecticidal protein is the most active known
B. thuringiensis toxin against the forest insect pest
Lymantria dispar (gypsy moth), unfortunately it is also highly toxic against the non-target insect
Bombyx mori (silk worm).
Results
Surface exposed hydrophobic residues over domains II and III were targeted for site-directed mutagenesis. Substitution of a phenylalanine residue (F328) by alanine reduced binding to the
Bombyx mori cadherin by 23-fold, reduced biological activity against
B. mori by 4-fold, while retaining activity against
Lymantria dispar.
Conclusion
The results identify a novel receptor-binding epitope and demonstrate that virtual elimination of binding to cadherin BR-175 does not completely remove toxicity in the case of
B. mori.
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