Activation of Bacillus thuringiensis Cry1I to a 50 kDa stable core impairs its full toxicity to Ostrinia nubilalis

Abstract Bacillus thuringiensis Cry1I insecticidal proteins are structurally similar to other three-domain Cry proteins, although their size, activity spectrum, and expression at the stationary phase are unique among other members of the Cry1 family. The mode of action of Cry1 proteins is not completely understood but the existence of an activation step prior to specific binding is widely accepted. In this study, we attempted to characterize and determine the importance of the activation process in the mode of action of Cry1I, as Cry1Ia protoxin or its partially processed form showed significantly higher toxicity to Ostrinia nubilalis than the fully processed protein either activated with …