Proteinase inhibitor genes provide resistance by:
Insect midgut proteases are essential for dietary protein digestion into amino acids required for growth and development. Many Lepidoptera rely predominantly on serine proteases trypsin, chymotrypsin, and elastase active at alkaline pH 10. Proteinase inhibitor genes from plants encode small disulfide-rich proteins that act as pseudo-substrates, tightly occupying enzyme active site forming stable enzyme-inhibitor complex with Ki in nanomolar range. Larvae ingesting inhibitor containing transgenic tissue cannot hydrolyze ingested protein, experience amino acid starvation, upregulate protease syn
Ref: Ryan Annu Rev Phytopathol 1990 inhibitors defense; Johnson PNAS 1989 trypsin; NCBI NBK21541; PubMed 1861469 proteinase inhibitor mode action.