Channel activity caused by a Bacillus thuringiensis delta-endotoxin preparation depends on the method of activation

The spontaneous insertion of Bacillus thuringiensis Cry delta-endotoxins into planar lipid bilayers to form discrete channels in the absence of receptors is the subject of conflicting reports in the literature. Because these proteins are synthesized as protoxins requiring proteolytic activation for conversion to the active form, differences in the in-vitro protocol used for this activation could be responsible for the contradictory results. To investigate this, CrylA(c) toxin was activated by different procedures, and its ability to release glucose entrapped within liposomes and to form channels in planar lipid bilayers assessed. The toxin preparations exhibited widely differing activities on the lipid membranes; SDS-PAGE and immunoblot analysis suggested that variations in the protein profile of the activated samples could be responsible. These findings raise important practical considerations for further in-vitro studies into the mechanism of action of these toxins.