Polycalin is involved in the action mechanism of Cry2Aa toxin in Helicoverpa armigera (Hübner)

Abstract

Receptor proteins on the brush border membrane of the insect midgut epithelium are involved in the mode of action of insecticidal Cry proteins from Bacillus thuringiensis (Bt). Polycalin has been identified as a binding protein of the Bt Cry1Ac toxin in several Lepidoptera including Helicoverpa armigera, but its role in the action mechanism of Cry2Aa is still unclear. In this study, we investigated the binding characteristics of polycalin from the midgut of H. armigera with Cry2Aa and its role in the toxicity of Cry2Aa. The results demonstrated that heterologously expressed H. armigera polycalin peptide could bind with Cry2Aa with high affinity (Kd=32 nmol L–1). The toxicity of Cry2Aa decreased by 27% after H. armigera larvae ingested polycalin antisera. These results suggested that polycalin could be a potential functional receptor for Cry2Aa, and it plays an important role in the susceptibility of H. armigera to Cry2Aa.