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 Britt

Research output: Contribution to journalArticle

2 Scopus citations

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)1093-1104
Number of pages12
JournalJournal of Biological Inorganic Chemistry
Volume23
Issue number7
DOIs
StatePublished - Oct 1 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

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