Mutations at the arginine residues in alpha 8 loop of Bacillus thuringiensis delta-endotoxin Cry1Ac affect toxicity and binding to Manduca sexta and Lymantria dispar aminopeptidase N

The functional role of the alpha8 loop residues in domain II of Bacillus th uringiensis Cry1Ac toxin was examined. Alanine substitution mutations were introduced in the residues from 275 to 293. Among the mutant toxins, substi tutions at R281 and R289 affected toxicity to Manduca sex-ta and Lymantria dispar. Loss of toxicity by these mutant toxins was well correlated with re ductions in binding affinity for brush border membrane vesicles and the pur ified receptor, aminopeptidase N (APN), from both insects, These data sugge st that the two arginine residues in the alpha8 loop region are important i n toxicity and APN binding in L. dispar and M. sexta. (C) 2001 Federation o f European Biochemical Societies. Published by Elsevier Science B,V, All ri ghts reserved.