The role of a proline-induced broken-helix motif in alpha-helix 2 of Bacillus thuringiensis delta-endotoxins

Bacillus thuringiensis delta -endotoxins (Cry proteins), are widely used fo r insect control and plant protection. They are water-soluble proteins that insert into membranes forming ion channels. In mast Cry toxins alpha -heli x 2 is broken by a highly conserved proline residue (Pro70 in Cry1Ab), gene rating a broken-helix motif. The flexibility. of the motif was altered thro ugh site-directed mutagenesis. It was found that increasing the flexibility of the motif decreased the stability the ion transport ability and the tox icity of the protein. By removing the broken-bells motif, the biological pr operties were restored to a wild type level. (C) 2001 Federation of Europea n Biochemical Societies. Published by Elsevier Science B.V. All rights rese rved.