Purification of Aminopeptidase N Protein and Differences in cDNAs Encoding APN1 Between Susceptible and Resistant Helicoverpa armigera Strains to Bacillus thuringiensis Toxins

The brush border membrane vesicles (BBMVs) in midgut of Helicoverpa armigera weresuccessfully separated, and most of the Aminopeptidase N (APN) activities in BBMV werepreserved. The 3-[(3-chlor-amidopropyl) dimethylammonio]-1-propane-sulphonate (CHAPS)can enhance the dissolution of BBMV, and phosphatidylinositol-specific phosopholipase C(PI-PLC) can cleave the APN from midgut membrane. The APN was primarily purified usinga Mono-Q column. The results of immunoblotting showed that the 120 and 170kDa proteinsin the BBMV could bind Cry1Ac, and 120kDa APN was a glycosylphosphalidylinositol(GPI)-anchored protein. Two Bt-resistant strains (Bt-P, Bt-M) were obtained after beingselected for more than five years in laboratory using Bt insecticides and Bt transgeniccotton incorporated into diet separately. The resistance of Bt-P and Bt-M were 1083.3and 48.7 times that of susceptible strain. The genes encoding APN1 in midgut ofsusceptible and resistant H.armigera were cloned by PCR and RACE techniques. Theinferred amino acid sequences of APN1 possessed the common character of APN family ininsects. In comparison with APN1 in susceptible strain, three nucleotide mutations wereobserved in the APN1 of Bt-M strain and resulted in two amino acid replace in theputative protein sequences, and eight nucleotide mutations were observed in Bt-P strainand resulted in five amino acid replace.