Partial purification and characterization of Bacillus thuringiensis Cry1A toxin receptor a from Heliothis virescens and cloning of the corresponding cDNA

Although extensively studied, the mechanism of action of insecticidal Bacil lus thuringiensis Cry toxins remains elusive and requires further elucidati on. Toxin receptors in the brush border membrane demand particular attentio n as they presumably initiate the cascade of events leading to insect morta lity after toxin activation. The 170-kDa Cry1Ac toxin-binding aminopeptidas e from the tobacco budworm (Heliothis virescens) was partially purified, an d its corresponding cDNA was cloned. The cDNA encodes a protein with a puta tive glycosyl phosphatidylinositol anchor and a polythreonine stretch clust ered near the C terminus with predicted O-glycosylation. Partial purificati on of the 170-kDa aminopeptidase also resulted in isolation of a 130-kDa pr otein that was immunologically identical to the 170-kDa protein, and the tw o proteins had identical N termini. These proteins were glycosylated, as su ggested by soybean agglutinin lectin blot results. Cry1Ac toxin affinity da ta for the two proteins indicated that the 130-kDa protein had a higher aff inity than the 170-kDa protein. The data suggest that posttranslational mod ifications can have a significant effect on Cry1A toxin interactions with s pecific insect midgut proteins.