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      New insights into the catalytic active-site structure of multicopper oxidases.

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          Abstract

          Structural models determined by X-ray crystallography play a central role in understanding the catalytic mechanism of enzymes. However, X-ray radiation generates hydrated electrons that can cause significant damage to the active sites of metalloenzymes. In the present study, crystal structures of the multicopper oxidases (MCOs) CueO from Escherichia coli and laccase from a metagenome were determined. Diffraction data were obtained from a single crystal under low to high X-ray dose conditions. At low levels of X-ray exposure, unambiguous electron density for an O atom was observed inside the trinuclear copper centre (TNC) in both MCOs. The gradual reduction of copper by hydrated electrons monitored by measurement of the Cu K-edge X-ray absorption spectra led to the disappearance of the electron density for the O atom. In addition, the size of the copper triangle was enlarged by a two-step shift in the location of the type III coppers owing to reduction. Further, binding of O2 to the TNC after its full reduction was observed in the case of the laccase. Based on these novel structural findings, the diverse resting structures of the MCOs and their four-electron O2-reduction process are discussed.

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          Author and article information

          Journal
          Acta Crystallogr. D Biol. Crystallogr.
          Acta crystallographica. Section D, Biological crystallography
          International Union of Crystallography (IUCr)
          1399-0047
          0907-4449
          Mar 2014
          : 70
          : Pt 3
          Affiliations
          [1 ] Faculty of Education, Kagawa University, 1-1 Saiwai-cho, Takamatsu, Kagawa 760-8522, Japan.
          [2 ] Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan.
          [3 ] Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology, Sapporo, Hokkaido 062-8517, Japan.
          [4 ] RIKEN SPring-8 Center, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan.
          Article
          S1399004713033051
          10.1107/S1399004713033051
          24598746

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