Characterization of trypsin- and chymotrypsin-like cDNAs from the gut of European corn borer (Ostrinia nubilalis)

Trypsin- and chymotrypsin-like serine proteases are the main digestive enzymes in lepidopteran midguts, and are considered the major proteases involved in Bacillus thuringiensis (Bt) protoxin activation or toxin detoxification. A previous report indicated that the reduced level of transcript T23 was associated with European corn borer (Ostrinia nubilalis) (ECB) resistance to Dipel® Bt formulations. Here we describe the sequence and the partial characterization of 17 trypsin- and 14 chymotrypsin-like proteases, which were identified from ECB gut-specific cDNA libraries. These putative trypsins and chymotrypsins have structural characteristics of serine proteases, including the catalytic triad of histidine, aspartic acid and serine, six conserved cystein residues; and other amino acids involved in substrate specificity. They also shared a high percent similarity with those of other lepidopteran species- Heliothis virescens, Manduca Sexta, and Helicoverpa armigera based on bootstrap amino acid consensus analysis. RT-PCR results indicated that all of these proteases were highly expressed in the midgut of ECB; however, there existed different expression profiles in other tissues, such as foregut, hindgut, haemolymph, fatbodies, silkglands, Malpighian tubules, and carcass. In addition to their roles in digestion, some of these proteases might also have other important physiological functions in other tissues.