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Nature. 2016 May 5;533(7601):58-63. doi: 10.1038/nature17938. Epub 2016 Apr 27.

Continuous evolution of Bacillus thuringiensis toxins overcomes insect resistance.

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Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Howard Hughes Medical Institute, Harvard University, Cambridge, Massachusetts 02138, USA.
Monsanto Company, 245 First Street, Suite 200, Cambridge, Massachusetts 02142, USA.
Department of Entomology, Cornell University, Geneva, New York 14456, USA.
Monsanto Company, 700 Chesterfield Parkway West, Chesterfield, Missouri 63017, USA.


The Bacillus thuringiensis δ-endotoxins (Bt toxins) are widely used insecticidal proteins in engineered crops that provide agricultural, economic, and environmental benefits. The development of insect resistance to Bt toxins endangers their long-term effectiveness. Here we have developed a phage-assisted continuous evolution selection that rapidly evolves high-affinity protein-protein interactions, and applied this system to evolve variants of the Bt toxin Cry1Ac that bind a cadherin-like receptor from the insect pest Trichoplusia ni (TnCAD) that is not natively bound by wild-type Cry1Ac. The resulting evolved Cry1Ac variants bind TnCAD with high affinity (dissociation constant Kd = 11-41 nM), kill TnCAD-expressing insect cells that are not susceptible to wild-type Cry1Ac, and kill Cry1Ac-resistant T. ni insects up to 335-fold more potently than wild-type Cry1Ac. Our findings establish that the evolution of Bt toxins with novel insect cell receptor affinity can overcome insect Bt toxin resistance and confer lethality approaching that of the wild-type Bt toxin against non-resistant insects.

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