Binding affinity and larvicidal activity of a novel vegetative insecticidal protein Vip3V

Bacillus thuringiensis (Bt) is a well-known entomo-pathogen. Strains of Bt. that are toxic to a variety of insects belonging to various orders such as Lepidoptera, Diptera and Coleoptra have been identified, their larvicidal proteins isolated, characterized and used extensively in agriculture for protecting the economically important crops against these pests. Recently a novel group of vegetative insecticidal genes, vip3S and vip3V coding for 789-amino acid (88.5 kDa) protein in Bacillus thuringiensis was cloned and expressed in Escherichia coli and found to be highly sensitive to most of the agricultural pests and even towards the resistant insects. The binding affinity of these toxins to the receptors of these insect pests and relation between the affinity and larvicidal activity were carried out. Labeling of the toxin proteins with radioactive 125I and preparation of the Brush border membrane vesicles of the receptors were carried out. Analysis of saturation kinetics (Kd) and binding constants (Bmax) by competition assays revealed direct correlation between the binding affinity of the toxin to the receptor and insect mortality.