Cry3Aa - Pesticidal crystal protein Cry3Aa precursor
Crystal proteins, δ-endotoxin family
Cry proteins are a product of Bacillus thuringiensis. During sporulation, the bacillus produces these pore-forming toxins which have insecticidal action. This has led to their use as insecticides, and more recently to genetically modified crops using Bt genes.
When insects ingest toxin crystals, their alkaline digestive tracts denature the insoluble crystals, making them soluble and thus amenable to being cut with proteases found in the insect gut, which liberate the toxin from the crystal. The Cry toxin is then inserted into the insect gut cell membrane, paralyzing the digestive tract and forming a pore.