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J. Bacteriol. doi:10.1128/JB.01336-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Crystal Structure of the NADH:Quinone Oxidoreductase WrbA from Escherichia coli

Institute for Microbiology and Genetics, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany; Department of Biochemistry and Molecular Biology, Eberly College of Science, The Pennsylvania State University, 205 South Frear Laboratory, University Park, PA 16802

^* To whom correspondence should be addressed. Email: susana.andrade{at}bio.uni-goettingen.de.

	Abstract

The flavoprotein WrbA, originally described as a tryptophan (W) repressor-binding protein in Escherichia coli has recently been shown to exhibit the enzymatic activity of a NADH:quinone oxidoreductase. This finding points towards a possible role in stress response and in the maintenance of a supply of reduced quinone. We have determined the three-dimensional structure of the WrbA holoprotein from E. coli at high resolution (1.66 Å) and we observe a characteristic, tetrameric quaternary structure highly similar to the one found in the WrbA homologs of Deinococcus radiodurans and Pseudomonas aeruginosa. A similar tetramer was originally observed in ISF, an iron-sulfur flavoprotein involved in the reduction of reactive oxygen species. Together with other, recently characterized proteins such as YhdA or YLR011wp (Lot6p), these tetrameric flavoproteins may constitute a large family with diverse functions in redox catalysis. WrbA binds substrates at an active site that provides an ideal stacking environment for aromatic moieties, while providing a pocket that is structured to stabilize the ADP part of an NADH molecule in its immediate vicinity. Structures of WrbA in complex with benzoquinone and NADH suggest a sequential binding mechanism for both molecules in the catalytic cycle.