Identification of Aedes aegypti specificity motifs in the N-terminus of the Bacillus thuringiensis Cry2Aa pesticidal protein

One advantage of using the Cry proteins of Bacillus thuringiensis as pesticides is their relatively narrow spectrum of activity, thus reducing the risk of non-target effects. Understanding the molecular basis of specificity has the potential to help us design improved products against emerging pests, or against pests that have developed resistance to other Cry proteins. Many previous studies have associated specificity with the binding of the Cry protein, particularly through the apical regions of domain II, to particular receptors on the midgut epithelial cells of the host insect. We have previously found that the specificity of Cry2A proteins against some insects is associated with domain I, which is traditionally associated with pore-formation but not receptor binding. In this work we identify four amino acids in the N-terminal region that, when mutated, can confer activity towards Aedes aegypti to Cry2Ab, a protein known to lack this toxicity. Intriguingly these amino acids are located in the region (amino acids 1–49) that is believed to be removed during proteolytic activation of the Cry protein. We discuss how the motifs containing these amino acids might be involved in the toxic process.