Structural and biochemical evidence for an enzymatic quinone redox cycle in Escherichia coli: identification of a novel quinol monooxygenase

J Biol Chem. 2005 Mar 4;280(9):8358-63. doi: 10.1074/jbc.M412637200. Epub 2004 Dec 21.


Naturally synthesized quinones perform a variety of important cellular functions. Escherichia coli produce both ubiquinone and menaquinone, which are involved in electron transport. However, semiquinone intermediates produced during the one-electron reduction of these compounds, as well as through auto-oxidation of the hydroxyquinone product, generate reactive oxygen species that stress the cell. Here, we present the crystal structure of YgiN, a protein of hitherto unknown function. The three-dimensional fold of YgiN is similar to that of ActVA-Orf6 monooxygenase, which acts on hydroxyquinone substrates. YgiN shares a promoter with "modulator of drug activity B," a protein with activity similar to that of mammalian DT-diaphorase capable of reducing mendione. YgiN was able to reoxidize menadiol, the product of the "modulator of drug activity B" (MdaB) enzymatic reaction. We therefore refer to YgiN as quinol monooxygenase. Modulator of drug activity B is reported to be involved in the protection of cells from reactive oxygen species formed during single electron oxidation and reduction reactions. The enzymatic activities, together with the structural characterization of YgiN, lend evidence to the possible existence of a novel quinone redox cycle in E. coli.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzoquinones / chemistry
  • Binding Sites
  • Crystallography, X-Ray
  • Dimerization
  • Drug Resistance, Neoplasm
  • Electron Transport
  • Electrons
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / physiology*
  • Mixed Function Oxygenases / chemistry*
  • Mixed Function Oxygenases / metabolism
  • Mixed Function Oxygenases / physiology*
  • Models, Chemical
  • Models, Molecular
  • Oxidation-Reduction*
  • Promoter Regions, Genetic
  • Protein Conformation
  • Protein Folding
  • Protein Structure, Secondary
  • Quinones / chemistry
  • Reactive Oxygen Species
  • Recombinant Proteins / chemistry
  • Spectrophotometry
  • Time Factors
  • Ubiquinone / chemistry
  • Vitamin K 2 / chemistry


  • Benzoquinones
  • Escherichia coli Proteins
  • MdaB protein, E coli
  • Quinones
  • Reactive Oxygen Species
  • Recombinant Proteins
  • Vitamin K 2
  • Ubiquinone
  • quinone
  • Mixed Function Oxygenases
  • 4-oxoquinoline monooxygenase
  • YgiN protein, E coli

Associated data

  • PDB/1R6Y
  • PDB/1TUV