Identification, Isolation, and Cloning of a Bacillus thuringiensis CryIAc Toxin-binding Protein from the Midgut of the Lepidopteran Insect Heliothis virescens

Bacillus thuringiensis toxins are insecticidal to a variety of insect species. The selectivity of the toxins produced by these bacteria is dependent on both the toxin structure and the receptor sites that are present in different insect species. One of these toxins, CryIAc, is highly insecticidal to the noctuid pest Heliothis virescens. Using toxin overlay assay, a 120-kDa glycoprotein was identified as a toxin-binding protein. This protein was partially purified, its N-terminal sequence was determined, and the full-length cDNA encoding this protein was isolated from a H. virescens midgut library. The B. thuringiensis toxin-binding protein, BTBP1, has high homology to aminopeptidase N from eukaryotes and prokaryotes.