A protein complex from Choristoneura fumiferana gut-juice involved in the precipitation of delta-endotoxin from Bacillus thuringiensis subsp. sotto.

A 75 kDa protein from spruce budworm (Choristoneura fumiferana) gut-juice has been isolated and shown to cause a specific precipitation of the delta-endotoxin from Bacillus thuringiensis subsp. sotto. This 75 kDa protein, separated by either column chromatography or SDS-PAGE, caused precipitation of the sotto toxin in both agarose diffusion gels and the PAGE gels. The precipitation event leads to limited proteolysis of the toxin and loss of larval toxicity. SDS-PAGE analysis of the precipitated toxin indicates that proteolysis of the toxin is not a prerequisite for precipitation. The protein responsible for precipitation, exhibits elastase-like activity and appears to be a complex which partially dissociates during boiling in SDS-PAGE sample buffer. Gut-juice from gypsy moth, forest tent caterpillar and white mark tussock moth also precipitated delta-endotoxin, but silkworm gut-juice gave a much weaker response. These results provide further evidence that, in the larval gut, differential processing of delta-endotoxin may play a role in the expression of activity towards various insect larvae.