Binding of Bacillus thuringiensis Cry1 toxins to the midgut brush border membrane vesicles of Chilo suppressalis (Lepidoptera : Pyralidae) : evidence of shared binding sites

Binding and competition among Cry1Aa, Cry1Ac, and Cry1Ba toxins were analyzed quantitatively #in vitro# by using 125 I-labeled activated toxins and brush border membrane vesicles isolated from #Chilo suppressalis# larval midguts. The three toxins bound specifically to the midgut brush border vesicles. Direct binding experiments showed that Cry1Aa and Cry1Ba recognized a single class of binding sites with different affinities, whereas Cry1Aa recognized two classes of binding sites, one with a high affinity and low concentration and the other with a lower affinity but higher concentration. Competition experiments showed that toxins Cry1Ac and Cry1Ba shared a binding site in the #C. suppressalis# midgut membranes and that this site was also the low-affinity binding site for Cry1Aa. (Résumé d'auteur