A specific binding protein from Manduca sexta for the insecticidal toxin of Bacillus thuringiensis subsp. berliner

Biopesticides based on the bacterium Bacillus thuringiensis have attracted wide attention as safe alternatives to chemical pesticides. In this paper, we report, for the first time, the identification and purification of a single binding protein from a lepidopteran insect, Manduca sexta, that is specific for a cryIA toxin of B. thuringiensis. The purified protein appeared as a single band of 210 kDa on a two-dimensional gel, had a pI of approximately 5.5, and stained with Schiff's reagent. The band material was sensitive to proteolytic digestion and was rich with acidic amino acids, indicating its protein nature. Radiolabeled toxin bound to the protein with a K_d value of 708 pM and could be specifically blocked by unlabeled toxin but not by toxins from other subspecies of B. thuringiensis. This study lays the groundwork to clone the toxin binding protein and to determine the molecular mechanism(s) of toxin action.