Abstract
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 α2β2γ2 subunit structure. Each active site has the nickel porphyrinoid F430 as a prosthetic group. In the active state, F430 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.
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Abbreviations
- CH3-S-CoM:
-
Methyl-coenzyme M
- CW:
-
Continuous wave
- EPR:
-
Electron paramagnetic resonance
- HS-CoB:
-
Coenzyme B
- HS-CoM:
-
Coenzyme M
- HYSCORE:
-
Hyperfine sublevel correlation
- MCR:
-
Methyl-coenzyme M reductase
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Acknowledgements
We thank the Swiss National Science Foundation (SNF) and the Fonds der Chemischen Industrie for financial support. D.H. gratefully acknowledges a research scholarship (HI 1094/1-1) from the Deutsche Forschungsgemeinschaft (DFG).
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Kern, D.I., Goenrich, M., Jaun, B. et al. Two sub-states of the red2 state of methyl-coenzyme M reductase revealed by high-field EPR spectroscopy. J Biol Inorg Chem 12, 1097–1105 (2007). https://doi.org/10.1007/s00775-007-0281-3
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DOI: https://doi.org/10.1007/s00775-007-0281-3