title: Exploiting the high-resolution crystal structure of Staphylococcus aureus MenH to gain insight into enzyme activity.
abstract: BACKGROUND
  MenH (2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate synthase) is a key enzyme in the biosynthesis of menaquinone, catalyzing an unusual 2,5-elimination of pyruvate from 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate.
  
  
  RESULTS
  The crystal structure of Staphylococcus aureus MenH has been determined at 2 Å resolution. In the absence of a complex to inform on aspects of specificity a model of the enzyme-substrate complex has been used in conjunction with previously published kinetic analyses, site-directed mutagenesis studies and comparisons with orthologues to investigate the structure and reactivity of MenH.
  
  
  CONCLUSIONS
  The overall basic active site displays pronounced hydrophobic character on one side and these properties complement those of the substrate. A complex network of hydrogen bonds involving well-ordered water molecules serves to position key residues participating in the recognition of substrate and subsequent catalysis. We propose a proton shuttle mechanism, reliant on a catalytic triad consisting of Ser89, Asp216 and His243. The reaction is initiated by proton abstraction from the substrate by an activated Ser89. The propensity to form a conjugated system provides the driving force for pyruvate elimination. During the elimination, a methylene group is converted to a methyl and we judge it likely that His243 provides a proton, previously acquired from Ser89 for that reduction. A conformational change of the protonated His243 may be encouraged by the presence of an anionic intermediate in the active site.
authors.affiliation: Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: Alice
authors.initials: A
authors.lastname: Dawson
authors.forename: Paul K
authors.initials: PK
authors.lastname: Fyfe
authors.forename: Florian
authors.initials: F
authors.lastname: Gillet
authors.forename: William N
authors.initials: WN
authors.lastname: Hunter
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D055162:Biocatalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006639:Histidine / Q000378:metabolism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011522:Protons; D019289:Pyruvic Acid / Q000378:metabolism; D016415:Sequence Alignment; D013211:Staphylococcus aureus / Q000201:enzymology*; D040681:Structural Homology, Protein; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D011522:Protons; D006639:Histidine; D019289:Pyruvic Acid