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 Tebo, Thomas G. Spiro, William H. Casey, R. David Britt

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Abstract

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.

Original languageEnglish (US)
Pages (from-to)1-12
Number of pages12
JournalJournal of Biological Inorganic Chemistry
DOIs
Publication statusAccepted/In press - Jul 2 2018

Keywords

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

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

Cite this

Mn(III) species formed by the multi-copper oxidase MnxG investigated by electron paramagnetic resonance spectroscopy. / Tao, Lizhi; Stich, Troy A.; Soldatova, Alexandra V.; Tebo, Bradley; Spiro, Thomas G.; Casey, William H.; Britt, R. David.

In: Journal of Biological Inorganic Chemistry, 02.07.2018, p. 1-12.

Research output: Contribution to journalArticle