title: The refined structure of the quinoprotein methanol dehydrogenase from Methylobacterium extorquens at 1.94 A.
abstract: BACKGROUND
  Methanol dehydrogenase (MDH) is a bacterial periplasmic quinoprotein; it has pyrrolo-quinoline quinone (PQQ) as its prosthetic group, requires Ca2+ for activity and uses cytochrome cL as its electron acceptor. Low-resolution structures of MDH have already been determined.
  
  
  RESULTS
  The structure of the alpha 2 beta 2 tetramer of MDH from Methylobacterium extorquens has now been determined at 1.94 A with an R-factor of 19.85%.
  
  
  CONCLUSIONS
  The alpha-subunit of MDH has an eight-fold radial symmetry, with its eight beta-sheets stabilized by a novel tryptophan docking motif. The PQQ in the active site is held in place by a coplanar tryptophan and by a novel disulphide ring formed between adjacent cysteines which are bonded by an unusual non-planar trans peptide bond. One of the carbonyl oxygens of PQQ is bonded to the Ca2+, probably facilitating attack on the substrate, and the other carbonyl oxygen is out of the plane of the ring, confirming the presence of the predicted free-radical semiquinone form of the prosthetic group.
authors.affiliation: Laboratory of Molecular Biophysics, University of Oxford, UK.
authors.forename: M
authors.initials: M
authors.lastname: Ghosh
authors.forename: C
authors.initials: C
authors.lastname: Anthony
authors.forename: K
authors.initials: K
authors.lastname: Harlos
authors.forename: M G
authors.initials: MG
authors.lastname: Goodwin
authors.forename: C
authors.initials: C
authors.lastname: Blake
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry; D003067:Coenzymes / Q000737:chemistry; D003196:Computer Graphics; D018360:Crystallography, X-Ray; D006088:Gram-Negative Aerobic Bacteria / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D045542:PQQ Cofactor; D011487:Protein Conformation; D015363:Quinolones / Q000737:chemistry
chemical_list: D003067:Coenzymes; D015363:Quinolones; D045542:PQQ Cofactor; D000429:Alcohol Oxidoreductases; C019641:alcohol dehydrogenase (acceptor); D002118:Calcium