The MtsA subunit of the methylthiol:coenzyme M methyltransferase of Methanosarcina barkeri catalyses both half-reactions of corrinoid-dependent dimethylsulfide: coenzyme M methyl transfer

J Biol Chem. 2001 Feb 9;276(6):4485-93. doi: 10.1074/jbc.M007514200. Epub 2000 Nov 9.

Abstract

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 K(eq) of 5 x 10(-)(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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Archaeal Proteins*
  • Base Sequence
  • Catalysis
  • DNA Primers
  • Kinetics
  • Methanosarcina barkeri / enzymology*
  • Methylation
  • Methyltransferases / chemistry
  • Methyltransferases / metabolism*
  • Sulfides / metabolism*
  • Vitamin B 12 / metabolism*

Substances

  • Archaeal Proteins
  • DNA Primers
  • Sulfides
  • Methyltransferases
  • methylcobalamin-coenzyme M methyltransferase
  • Vitamin B 12