Two sub-states of the red2 state of methyl-coenzyme M reductase revealed by high-field EPR spectroscopy.
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.
Kern
Denise I
DI
Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, Zurich, Switzerland.
Goenrich
Meike
M
Jaun
Bernhard
B
Thauer
Rudolf K
RK
Harmer
Jeffrey
J
Hinderberger
Dariush
D
D019843:Archaeal Proteins / Q000737:chemistry*; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D017013:Methanobacteriaceae / Q000201:enzymology*; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*
D019843:Archaeal Proteins; D009532:Nickel; D010088:Oxidoreductases; C021572:methyl coenzyme M reductase
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