Determination of Receptor Binding Properties of Bacillus thuringiensis Endotoxins to Cotton Bollworm (Helicoverpa zea) and Pink Bollworm (Pectinophora gossypiella) Midgut Brush Border Membrane Vesicles

Pesticidal activity and receptor binding properties of Bacillus thuringiensis toxins to cotton pink bollworm (Pectinophora gossypiella) and cotton bollworm (Helicoverpa zea) were investigated. P. gossypiella was susceptible to CrylAa, CrylAb, CrylAc, and Cry2Aa toxins. To H. zea, CrylAc and CrylAb were more potent than CrylAa and Cry2Aa. CrylBa, Cry1Ca, Cry I Da, CrylEa, CrylFa, CrylGa, Cry I Ha, and Cry2Ba were not potent against both pests. Binding assays were performed with I-labeled toxins (CrylAa, CrylAb, CrylAc, and Cry2Aa) and brush border membrane vesicles (BBMVs) prepared from H. zea and P. gossypiella midguts. Both CrylAb and CrylAc toxins showed saturable, high-affinity binding to P. gossypiella and H. zea BBMVs. Cry2Aa and CrylAa toxins bound to BBMVs with relatively low binding affinity but with high binding site concentration. Heterologous competition binding assays were performed to investigate the binding site cross reactivity. The results showed that CrylAa, CrylAb, and CrylAc recognize the same binding site, which is different from Cry2Aa. Ligand blot assay showed that CrylAc toxin binds to a 120kDa BBMV protein in P. gossypiella and CrylAb binds to a major 210-kDa protein.