Characterization of four midgut aminopeptidase N isozymes from Ostrinia furnacalis strains with different susceptibilities to Bacillus thuringiensis.

The full-length cDNA of four Ofapn aminopeptidases were cloned and sequenced from susceptible and resistant Ostrinia furnacalis strains. Four sequences were identified as APN because they shared the common structural features with APN from Lepidoptera, including the signal peptide, GPI anchor signal, the zinc binding/gluzincin motif HEX2HX18E and the gluzincin aminopeptidase motif GAMEN. Compared with APN sequences from the susceptible strain, there were 9, 5, 10 and 12 amino acid variations in the deduced protein sequences from the resistant strain. There were also differences in mRNA expression of the four Ofapn genes between resistant and susceptible O. furnacalis strains.