The role of a proline-induced broken-helix motif in α-helix 2 of Bacillus thuringiensis δ-endotoxins

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 mast 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-bells motif, the biological properties were restored to a wild type level. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.