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Unformatted text preview: Molecular basis for the herbicide resistance of Roundup Ready crops Todd Funke , Huijong Han , Martha L. Healy-Fried , Markus Fischer , and Ernst Scho nbrunn Department of Medicinal Chemistry, University of Kansas, Lawrence, KS 66045; and Department of Organic Chemistry and Biochemistry, Technical University Munich, D-85747 Garching, Germany Edited by Brian W. Matthews, University of Oregon, Eugene, OR, and approved July 12, 2006 (received for review May 3, 2006) The engineering of transgenic crops resistant to the broad-spec- trum herbicide glyphosate has greatly improved agricultural effi- ciency worldwide. Glyphosate-based herbicides, such as Roundup, target the shikimate pathway enzyme 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase, the functionality of which is abso- lutely required for the survival of plants. Roundup Ready plants carry the gene coding for a glyphosate-insensitive form of this enzyme, obtained from Agrobacterium sp. strain CP4. Once incor- porated into the plant genome, the gene product, CP4 EPSP synthase, confers crop resistance to glyphosate. Although widely used, the molecular basis for this glyphosate-resistance has re- mained obscure. We generated a synthetic gene coding for CP4 EPSP synthase and characterized the enzyme using kinetics and crystallography. The CP4 enzyme has unexpected kinetic and structural properties that render it unique among the known EPSP synthases. Glyphosate binds to the CP4 EPSP synthase in a con- densed, noninhibitory conformation. Glyphosate sensitivity can be restored through a single-site mutation in the active site (Ala-100 Gly), allowing glyphosate to bind in its extended, inhibitory conformation. conformational change u crystal structure u genetic modification u mutation T he broad-spectrum herbicide glyphosate, the active ingredi- ent of Roundup, inhibits 5-enolpyruvylshikimate-3- phosphate (EPSP) synthase (EC 188.8.131.52), the enzyme catalyzing the penultimate step of the shikimate pathway toward the biosynthesis of aromatic amino acids. Roundup Ready crop lines contain a gene derived from Agrobacterium sp. strain CP4, encoding a glyphosate-tolerant enzyme, the so-called CP4 EPSP synthase (1, 2). Expression of CP4 EPSP synthase results in glyphosate-tolerant crops, enabling more effective weed control by allowing postemergent herbicide application. The substantial advantages of glyphosate-tolerant crops have resulted in rapid adoption: 87% of soybeans, 61% of cotton, and 26% of corn planted in the United States in 2005 were glyphosate-tolerant varieties (3). However, lingering concerns about the potential health and environmental effects of genetically modified organ- isms have limited the acceptance of such seed lines and food products, particularly in Europe and Japan....
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