This family contains insecticidal toxins produced by Bacillus species of bacteria. During spore formation the bacteria produce crystals of this protein. When an insect ingests these proteins they are activated by proteolytic cleavage. The N terminus is cleaved in all of the proteins and a C terminal extension is cleaved in some members. Once activated the endotoxin binds to the gut epithelium and causes cell lysis leading to death. This activated region of the delta endotoxin is composed of three structural domains. The N-terminal helical domain is involved in membrane insertion and pore formation. The second and third domains are involved in receptor binding.

1: Crystal structure of insecticidal delta-endotoxin from Bacillus thuringiensis at 2.5 angstroms resolution. Li J, Carroll J, Ellar DJ; Nature 1991;353:815-821. PMID:1658659

2: Bacillus thuringiensis and its pesticidal crystal proteins. Schnepf E, Crickmore N, Van Rie J, Lereclus D, Baum J, Feitelson J, Zeigler DR, Dean DH; Microbiol Mol Biol Rev 1998;62:775-806. PMID:9729609