Promotes colloidosmotic lysis by binding to the midgut epithelial cells of insects. The crystal protein is produced during sporulation and is accumulated both as an inclusion and as part of the spore coat. Toxic segment of the protein is located in the N-terminus. Diverse amino acid mutations in sequence block 667-676 have no direct effect on the insecticidal activity but alter the structural stability of the toxin protein molecule. Belongs to the delta endotoxin family.