Two sub-states of the red2 state of methyl-coenzyme M reductase revealed by high-field EPR spectroscopy.

Journal article

Methyl-coenzyme M reductase (MCR) catalyzes the formation of methane from methyl-coenzyme M and coenzyme B in methanogenic archaea. The enzyme has two structurally interlinked active sites embedded in an alpha(2)beta(2)gamma(2) subunit structure. Each active site has the nickel porphyrinoid F(430) as a prosthetic group. In the active state, F(430) contains the transition metal in the Ni(I) oxidation state. The active enzyme exhibits an axial Ni(I)-based continuous wave (CW) electron paramagnetic resonance (EPR) signal, called red1a in the absence of substrates or red1c in the presence of coenzyme M. Addition of coenzyme B to the MCR-red1 state can partially and reversibly convert it into the MCR-red2 form, which shows a rhombic Ni(I)-based EPR signal (at X-band microwave frequencies of approximately 9.4 GHz). In this report we present evidence from high-field/high-frequency CW EPR spectroscopy (W-band, microwave frequency of approximately 94 GHz) that the red2 state consists of two substates that could not be resolved by EPR spectroscopy at X-band frequencies. At W-band it becomes apparent that upon addition of coenzyme B to MCR in the red1c state, two red2 EPR signals are induced, not one as was previously believed. The first signal is the well-characterized (ortho)rhombic EPR signal, thus far called red2, while the second previously unidentified signal is axial. We have named the two substates MCR-red2r and MCR-red2a after their rhombic and axial signals, respectively.

Authors: Kern, D; Goenrich, M; Jaun, B; Thauer, R; Harmer, J

• Publication status: Published
• Journal: Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry
• Volume: 12
• Issue: 8
• Pages: 1097-1105
• Publication date: 2007-11-01
• DOI: 10.1007/s00775-007-0281-3
• EISSN: 1432-1327
• ISSN: 0949-8257
• Language: English
• Keywords: Archaeal Proteins; Electron Spin Resonance Spectroscopy; Nickel; Oxidation-Reduction; Oxidoreductases; Binding Sites; Methanobacteriaceae