Cadherin Protein Enhances Bt Toxicity

Bacillus thuringiensis (Bt) Cry1A are proteins toxic only to insect larvae in the order Lepidoptera. This family of toxins is widely used for insect control with Bt-transgenic crops, particularly cotton, and in Bt microbial pesticides. Several models are proposed for the mode of action of Cry1A toxins, but in all the models, the monomeric form of the toxin binds to Bt-R1, a specific cadherin first characterized from the midgut of the tobacco hornworm. Cadherins are proteins that play important functions in cell to cell adhesion (as a sort of glue holding cells together in a tissue). A specific part of this cadherin, CR12-MPED, was reported to be the functional receptor region for Cry1Ab binding and toxicity.  

Jiang Chen and colleagues from the University of Georgia observed an increase in insect mortality if purified CR12-MPED is introduced together with Cry1Ab to the tobacco hornworm (Manduca sexta). Although its synergistic mechanism is not yet fully characterized, CR12-MPED peptide has the potential to augment the control of lepidopteran pests by Cry1A toxins. This synergist is a good candidate for the development of a more effective strategy to control lepidopteran pests that are currently not being efficiently controlled by Bt crops. Current researches focus on the action of CR12-MPED toward other insect groups. But because homologues of Bt-R1 cadherin are present in other lepidopteran species, it is likely that CR12-MPED may also enhance Cry1A toxicity towards alternative lepidopteran pests.

The article published by PNAS is available at http://www.pnas.org/cgi/reprint/104/35/13901