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J. Biol. Chem., Vol. 276, Issue 6, 4485-4493, February 9, 2001
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From the Department of Microbiology, Ohio State University,
Columbus, Ohio 43210
Methanogenesis from dimethylsulfide
requires the intermediate methylation of coenzyme M. This reaction is
catalyzed by a methylthiol:coenzyme M methyltransferase composed of two
polypeptides, MtsA (a methylcobalamin:coenzyme M methyltransferase) and
MtsB (homologous to a class of corrinoid proteins involved in
methanogenesis). Recombinant MtsA was purified and found to be a
homodimer that bound one zinc atom per polypeptide, but no
corrinoid cofactor. MtsA is an active
methylcobalamin:coenzyme M methyltransferase, but also methylates
cob(I)alamin with dimethylsulfide, yielding equimolar
methylcobalamin and methanethiol in an endergonic reaction with a
Keq of 5 × 10
The MtsA Subunit of the Methylthiol:Coenzyme M Methyltransferase
of Methanosarcina barkeri Catalyses Both Half-reactions
of Corrinoid-dependent Dimethylsulfide: Coenzyme M
Methyl Transfer*
, and
4.
MtsA and cob(I)alamin mediate dimethylsulfide:coenzyme M methyl transfer in the complete absence of MtsB. Dimethylsulfide inhibited methylcobalamin:coenzyme methyl transfer by MtsA. Inhibition by dimethylsulfide was mixed with respect to methylcobalamin, but competitive with coenzyme M. MtbA, a MtsA homolog participating in
coenzyme M methylation with methylamines, was not inhibited by
dimethylsulfide and did not catalyze detectable
dimethylsulfide:cob(I)alamin methyl transfer. These results are most
consistent with a model for the native methylthiol:coenzyme M
methyltransferase in which MtsA mediates the methylation of corrinoid
bound to MtsB with dimethylsulfide and subsequently demethylates
MtsB-bound corrinoid with coenzyme M, possibly employing elements of
the same methyltransferase active site for both reactions.
*
This work was supported by U.S. Department of Energy Grant
DE-FG-02-91ER20042.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Biophysics Research Div., University of Michigan,
Ann Arbor, MI 48109.
§
To whom correspondence should be addressed. Tel.: 614-292-1578;
Fax: 614-292-8120; E-mail: krzycki.1@osu.edu.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.
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