title: How the mutation glycine96 to alanine confers glyphosate insensitivity to 5-enolpyruvyl shikimate-3-phosphate synthase from Escherichia coli.
abstract: The enzyme 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase (EC 2.5.1.19) is essential for the biosynthesis of aromatic compounds in plants and microbes and is the unique target of the herbicide glyphosate. One of the first glyphosate-insensitive enzymes reported was a Gly96Ala mutant of EPSP synthase from Klebsiella pneumoniae. We have introduced this single-site mutation into the highly homologous EPSP synthase from Escherichia coli. The mutant enzyme is insensitive to glyphosate with unaltered affinity for its first substrate, shikimate-3-phosphate (S3P), but displays a 30-fold lower affinity for its second substrate, phosphoenolpyruvate (PEP). Using X-ray crystallography, we solved the structure of Gly96Ala-EPSP synthase liganded with S3P to 0.17 nm resolution. The crystal structure shows that the additional methyl group from Ala96 protrudes into the active site of the enzyme. While the interactions between enzyme and S3P remain unaffected, the accessible volume for glyphosate binding is substantially reduced. Exploiting the crystallographic results for molecular modeling, we demonstrate that PEP but not glyphosate can be docked in the Gly96Ala-modified binding site. The predicted PEP binding site satisfies the earlier proposed interaction pattern for PEP with EPSP synthase and corroborates the assumption that glyphosate and PEP target the same binding site.
authors.affiliation: Max-Planck Institute for Medical Research, Department of Biophysics, 69120 Heidelberg, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Eschenburg
authors.forename: Martha L
authors.initials: ML
authors.lastname: Healy
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Priestman
authors.forename: Gerald H
authors.initials: GH
authors.lastname: Lushington
authors.forename: Ernst
authors.initials: E
authors.lastname: Schönbrunn
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D000409:Alanine / Q000235:genetics*; D019883:Alkyl and Aryl Transferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D001665:Binding Sites / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics* / Q000494:pharmacology*; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000201:enzymology; D008958:Models, Molecular; D009154:Mutation; D010728:Phosphoenolpyruvate / Q000737:chemistry / Q000378:metabolism; D012765:Shikimic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D000409:Alanine; D019883:Alkyl and Aryl Transferases; D005998:Glycine; D010728:Phosphoenolpyruvate; D012765:Shikimic Acid; D000097797:Glyphosate; C042786:shikimic acid-3-phosphate