Incorporation of Protease K into Larval Insect Membrane Vesicles Does Not Result in Disruption of Integrity or Function of the Pore-Forming Bacillus thuringiensis δ-Endotoxin

Bacillus thuringiensis δ-endotoxins insert into the brush border membranes of insect larval cells to form ion channels. A possible interaction of these toxins with a cytoplasmic component was examined by preloading vesicles from insect larval cells with protease K followed by incubation with toxin. There was no evidence for toxin antigens smaller than the intact toxin in extracts of solubilized vesicles, nor was there an effect of the inclusion of protease K on either of two functional properties, the formation of toxin aggregates or of ion pores. These toxins, physically and functionally, appear to be confined to the membrane.