JBIC Journal of Biological Inorganic Chemistry

, Volume 23, Issue 7, pp 1093–1104 | Cite as

Mn(III) species formed by the multi-copper oxidase MnxG investigated by electron paramagnetic resonance spectroscopy

  • Lizhi Tao
  • Troy A. Stich
  • Alexandra V. Soldatova
  • Bradley M. Tebo
  • Thomas G. Spiro
  • William H. Casey
  • R. David BrittEmail author
Original Paper
Part of the following topical collections:
  1. Alison Butler: Papers in Celebration of Her 2018 ACS Alfred Bader Award in Bioorganic or Bioinorganic Chemistry


The multi-copper oxidase (MCO) MnxG from marine Bacillus bacteria plays an essential role in geochemical cycling of manganese by oxidizing Mn2+(aq) to form manganese oxide minerals at rates that are three to five orders of magnitude faster than abiotic rates. The MCO MnxG protein is isolated as part of a multi-protein complex, denoted as Mnx, which includes one MnxG unit and a hexamer of MnxE3F3 subunit. During the oxidation of Mn2+(aq) catalyzed by the Mnx protein complex, an enzyme-bound Mn(III) species was trapped recently in the presence of pyrophosphate (PP) and analyzed using parallel-mode electron paramagnetic resonance (EPR) spectroscopy. Herein, we provide a full analysis of this enzyme-bound Mn(III) intermediate via temperature dependence studies and spectral simulations. This Mnx-bound Mn(III) species is characterized by a hyperfine-coupling value of A(55Mn) = 4.2 mT (corresponding to 120 MHz) and a negative zero-field splitting (ZFS) value of D = − 2.0 cm−1. These magnetic properties suggest that the Mnx-bound Mn(III) species could be either six-coordinate with a 5B1g ground state or square-pyramidal five-coordinate with a 5B1 ground state. In addition, as a control, Mn(III)PP is also analyzed by parallel-mode EPR spectroscopy. It exhibits distinctly different magnetic properties with a hyperfine-coupling value of A(55Mn) = 4.8 mT (corresponding to 140 MHz) and a negative ZFS value of D = − 2.5 cm−1. The different ZFS values suggest differences in ligand environment of Mnx-bound Mn(III) and aqueous Mn(III)PP species. These studies provide further insights into the mechanism of biological Mn2+(aq) oxidation.


Parallel-mode EPR Multi-copper oxidase MnxG Mnx protein complex Mn(II) oxidation Zero-field splitting 



The work was supported by the National Science Foundation Award Numbers CHE-1213699, CHE-1665455 to RDB, EAR-1231322 to WHC, CHE-1410688 to BMT, and CHE-1410353 to TGS. The EPR spectrometers at the CalEPR facility used in this study were funded by the National Institutes of Health (S10-RR021075) and the NSF (CHE-1048671).


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Copyright information

© SBIC 2018

Authors and Affiliations

  • Lizhi Tao
    • 1
  • Troy A. Stich
    • 1
  • Alexandra V. Soldatova
    • 3
  • Bradley M. Tebo
    • 4
  • Thomas G. Spiro
    • 3
  • William H. Casey
    • 1
    • 2
  • R. David Britt
    • 1
    Email author
  1. 1.Department of ChemistryUniversity of CaliforniaDavisUSA
  2. 2.Department of GeologyUniversity of CaliforniaDavisUSA
  3. 3.Department of ChemistryUniversity of WashingtonSeattleUSA
  4. 4.Division of Environmental and Biomolecular SystemsOregon Health and Science UniversityPortlandUSA

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