Processing of Delta Endotoxin from Bacillus thuringiensis Subspp.Kurstaki HD-1 and HD-73 by Immobilized Trypsin and Chymotrypsin

Insecticidal crystal proteins (delta-endotoxins, ICPs)from Bacillus thuringiensis subspp. kurstaki HD-73 and HD-1 were digested by trypsin and chymotrypsin that were immobilized onto CNBr-Sepharose 4B. In a six-hour digestion, both enzymes generated proteolytic resistant cores having 65 kDa molecular size from both ICPs. The ICP from HD-73 generated two other higher molecular intermediates, i.e. 95 and 80 kDa fragments, by the trypsin treatment. This suggested that the ICP of HD-73 might have three sites susceptible to trypsin. ICP from HD-1, however, was more quickly digested by both enzymes and the intermediate pattern in SDS-PAGE was completely different from that of the ICP from HD-73, suggesting that the main protein of ICP from HD-73, a product of crylA(c) gene, contains significantly fewer HD-1 crystals. N-terminus amino acid residue of the resistant core derived from HD-73 was the same as the sequence starting from the 29th residue in the crylA gene product, 130 kDa protein. The core generated by both enzymes from HD-1 and HD-73 showed insecticidal activity against the diamondback moth, Plutella xylostella, the smaller tea tortrix, Adoxophyes sp., and the common cutworm, Spodoptera litura.