Substitution of residues on the proximal side of Cry1A Bacillus thuringiensis delta-endotoxins affects irreversible binding to Manduca sexta midgut membrane.
Substitution of a positively charged residue (R93F) or addition of a negatively charged residue (A92D) at the N-terminal of alpha 3 helix of domain I of the Cry1Ac delta-endotoxin resulted in a substantial reduction in toxicity against Manduca sexta. The N-terminal residues of helix 3 are considered to be on the same (proximal) surface of the toxin as the loops in domain II which are involved in the binding of the toxin to the receptor. The loss of toxicity was not caused by a decrease in the initial binding but rather by reduced irreversible binding. Only 65 and 75% of the A92D and R93F mutant toxin, respectively, bound to midgut vesicles irreversibly, compared to 94% of the wild type toxin. On the other hand, replacing A119 in a loop on the distal side of the helices with negatively charged residues (A119D or A119E) did not affect toxicity or irreversible binding.
Hussain
S R
SR
Molecular, Cellular and Developmental Biology (MCDB) Program, Ohio State University, Columbus 43210, USA.
Aronson
A I
AI
Dean
D H
DH
D000595:Amino Acid Sequence; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D001427:Bacterial Toxins; D004731:Endotoxins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D006460:Hemolysin Proteins; D007413:Intestinal Mucosa / Q000378:metabolism*; D018402:Manduca / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010572:Pest Control, Biological; D011485:Protein Binding
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis