38th Annual Meeting of the Society for Invertebrate Pathology

Binding molecules located in the midgut epithelium are key factors in the action of Bacillus thuringiensis (Bt) toxins. Cadherins are primary receptors for Cry1A toxins in Lepidoptera because of their high affinity for Cry toxins, ability to catalyze toxin-induced cell death and ‘knockout’ mutations result in resistance. Although there is significant homology between cadherins from different lepidopterans, each cadherin has different affinity for specific Cry toxins. Our data indicate that toxin-binding cadherins are localized to the tips and ‘hammock’ regions of microvilli in brush border epithelium. Aminopeptidases and membrane-bound alkaline phosphatases that bind toxin, are anchored by glycosylphosphatidyl inositol which is presumably related to their localization in lipid rafts, and are primarily distributed along microvilli in the posterior region of Manduca sexta larvae. Glycolipids are receptors for Bt toxins in nematodes and insects. Loss of glycolipid carbohydrates causes toxin resistance in Caenorhabditis elegans. In both nematodes and insects glycolipids specifically bind Bt toxins. The role of binding proteins in toxin action has evolved from arguments about whether aminopeptidases or cadherins are functional receptors to a model that integrates multiple binding proteins and even glycolipids into toxin action. The implications of multiple receptors and their toxin specificities for pest insect control will be discussed.