Overview for MACiE Entry M0156
EC Number: 184.108.40.206 (A member of the Transferases, Transferring sulfur-containing groups, Transferring alkylthio groups)
Enzyme Name: coenzyme-B sulfoethylthiotransferase
Biological Species: Methanobacterium thermoautotrophicum (Bacteria)
Catalytic Chain UniprotKB Accession Codes:
- P11558 - Methyl-coenzyme M reductase I subunit alpha
- P11560 - Methyl-coenzyme M reductase I subunit beta
Representative PDB Code: 1mro - METHYL-COENZYME M REDUCTASE (Resolution = 1.16 Å).
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This reaction is irreversible.
Overall Comment: There are at least two proposed alternative mechanisms for this reaction. The mechanism depicted here is better supported by stereochemical and energetic factors [1,3]. However it should be noted that it is still unclear which mechanism is the correct one . The second mechanism proposed assumes that the first step is the attack by the Ni(I) on the thioether sulfur of methyl-coenzyme M. This yields a free methyl radical which reacts with the thiol group of coenzyme B to give methane and the coenzyme B thiyl radical . Ni is from the hydroporphinoid nickel complex coenzyme Factor 430.
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Stepwise Description of the Reaction
|Step 1||Nickel (Ni(I)) of factor 430 attacks the methyl group of the methylated coenzyme M, which is reprotonated from Tyr367E. Nickel assumed the Ni(III) oxidation state.|
|Step 2||Tyr367E deprotonates coenzyme M, causing it to donate a single electron to the Ni(III) ion of factor 430.|
|Step 3||The methyl group deprotonates Tyr367E whilst disassociating from Ni(II) in factor 430. Tyr367E immediately deprotonates coenzyme B.|
|Step 4||The thiolate of coenzyme B attacks the thiyl radical of coenzyme M in a coordination reaction.|
|Step 5||The thiyl radical of coenzyme M donates a second electron to the nickel of factor 430, regenerating the Ni(I) oxidation state.|
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Catalytic Residues Involved
||Location of Function
Organic Cofactors for M0156
Metal Cofactors for M0156
- W. Grabarse et al. (2001), J. Mol. Biol., 309, 315-330. On the mechanism of biological methane formation: structural evidence for conformational changes in methyl-coenzyme M reductase upon substrate binding.
- V. Pelmenschikov et al. (2002), J. Am. Chem. Soc., 124, 4039-4049. A mechanism from quantum chemical studies for methane formation in methanogenesis.
- M. Goenrich et al. (2004), J. Biol. Inorg. Chem., 9, 691-705. Probing the reactivity of Ni in the active site of methyl-coenzyme M reductase with substrate analogues.
- U. Ermler (2005), Dalton Trans., 21, 3451-3458. On the mechanism of methyl-coenzyme M reductase.
Homologue information for M0156 (1mro)
MACiE Homologues (within the PDB)
MACiE Homologues (within UniprotKB/SwissProt)
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