Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

J Biol Inorg Chem. 2007 Sep;12(7):1083-94. doi: 10.1007/s00775-007-0278-y. Epub 2007 Aug 14.

Abstract

MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV-vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Outer Membrane Proteins / chemistry*
  • Cytochrome c Group / chemistry*
  • Cytochrome c Group / isolation & purification
  • Cytochromes / chemistry*
  • Electron Spin Resonance Spectroscopy
  • Electron Transport
  • Heme / chemistry*
  • Potentiometry
  • Respiration
  • Shewanella / chemistry*

Substances

  • Bacterial Outer Membrane Proteins
  • Cytochrome c Group
  • Cytochromes
  • Heme
  • MtrC protein, Shewanella