The role of a proline‐induced broken‐helix motif in α‐helix 2 of <i>Bacillus thuringiensis</i> δ‐endotoxins

Abstract

Bacillus thuringiensis delta-endotoxins (Cry proteins), are widely used for insect control and plant protection. They are water-soluble proteins that insert into membranes forming ion channels. In most Cry toxins alpha-helix 2 is broken by a highly conserved proline residue (Pro70 in Cry1Ab), generating a broken-helix motif. The flexibility of the motif was altered through site-directed mutagenesis. It was found that increasing the flexibility of the motif decreased the stability, the ion transport ability and the toxicity of the protein. By removing the broken-helix motif, the biological properties were restored to a wild type level.