In Silico Structure-Based Identification and Validation of Key Residues of Vip3Aa Involving in Lepidopteran Brush Border Receptor Binding

The vegetative insecticidal proteins (VIPs) of Bacillus thuringiensis (Bt) have a broad-spectrum insecticidal activity against Lepidopteran pests and no cross-resistance with the insecticidal crystal protein Cry protein. So there are great potentials for the control of agricultural pests and the resolution of resistance problems. The structural information of Vip3Aa protein and the predicted key amino acid sites on the C-terminal domain of Vip3Aa were analyzed with the methods of bioinformatics such as homology modeling and molecular docking. Site-directed mutagenesis was used to replace these amino acids with alanine, and there was difference in the activities of the mutant protein and Vip3Aa protein. Y619A had improved insecticidal activity against Helicoverpa armigera, but the toxicity of W552A and E627A to Helicoverpa armigera was significantly reduced. The mutants of W552A and E627A had reduced insecticidal activity against Spodoptera exigua. This study demonstrated that the C-terminal domain played an important role in the function of Vip3Aa protein toxin, and the deletion of the side chain of key residues had a significant effect on the activity of the insecticidal protein. This study provides the theoretical basis for revealing the relationship between the structure and function of Vip3Aa protein.