Proteins of 65 and 57 kD were isolated from the apical membranes of midgut epithelium of Anopheles stephensi larvae by affinity chromatography. These proteins can specifically bind endotoxin Cry11A and activate toxin Cry4B (Cry4B-tox) under conditions of ligand blotting, and both Cry proteins compete for this binding. At least in the case of Cry4B-tox, the binding with 65 and 57 kD proteins is reversible. The ability of the products of limited proteolysis of Cry11A and Cry4B to bind the 65 and 57 kD proteins correlates with their toxicity to A. stephensi larva. The N-terminal amino acid sequence of the 57 kD protein is unique and absent in the NCBI GenBank. The proteins of 65 and 57 kD share most of the properties studied with Aedes aegypti toxin-binding proteins. It is possible that they altogether represent a novel class (or classes) of δ-endotoxin receptors.

The dynamics of pathological changes in the intestine of Aedes aegypti larvae under the influence of toxins Cry11A and Cry4B produced by Bacillus thuringiensis israelensis was studied by means of electron microscope. Most significant ultrastructure changes in the intestine of the second instar larvae were observed in the midgut. The cytoplasm of cells disintegrated, and elongated lacunae appeared. The number of microvilli decreased, or they disappeared in the result of destruction. The peritrophic membrane displaced to the lumen of midgut. Any changes in epithelial cells and cuticle in time of foregut and hindgut were not observed in a comparison to control. The toxin Cry4B caused the most effective destruction of the midgut epithelium.