Investigation on the difference of insecticidal activities between Vip3Aa11 and Vip3Aa39 proteins againstHelicoverpa armigera(Insecta: Lepidoptera)

Vip3Aa11 and Vip3Aa39 were isolated from Bacillus thuringiensis strains C9 and T03B001, respectively. Despite that there is 95.06% similarity of amino acid sequences between these two proteins, the insecticidal activity of them against Helicoverpa armigera is different and their LC50 were 35 µg/ml and 120 µg/ml, respectively. In order to explore the causes of differences in the insecticidal activity of these two proteins, we have examined the trypsin sensitivity assay and the assay binding with the brush border membrane vesicles of Helicoverpa armigera. The experiment of treatment with trypsin indicated that there is no difference in sensitivity between these two proteins, as both proteins were able to bind to the midgut BBMV of Helicoverpa armigera. However, the binding ability of Vip3Aa11 was stronger than that of Vip3Aa39. The ligand-blotting analysis demonstrated both biotinylated Vip3Aa11 and Vip3Aa39 toxins primarily showed binding to four midgut putative receptor proteins of 65, 80, 100 and 120 kDa. These results provide that the causes for the different insecticidal activity between these two proteins against Helicoverpa armigera may be due to the difference in binding ability on BBMV.