1. Chloromethane:tetrahydrofolate methyl transfer by two proteins fromMethylobacterium chloromethanicumstrain CM4
- Author
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Erhard Stupperich, Alex Studer, Thomas Leisinger, and Stéphane Vuilleumier
- Subjects
Methyltransferase ,biology ,Stereochemistry ,Chloromethane ,Corrin ,biology.organism_classification ,Biochemistry ,Cofactor ,chemistry.chemical_compound ,Corrinoid ,chemistry ,biology.protein ,Methylobacterium ,Dehalogenase ,Methyl group - Abstract
The cmuA and cmuB genes are required for growth of Methylobacterium chloromethanicum strain CM4 with chloromethane as the sole carbon source. While CmuB was previously shown to possess methylcobalamin:tetrahydrofolate methyltransferase activity, sequence analysis indicated that CmuA represented a novel and so far unique two-domain methyltransferase/corrinoid-binding protein involved in methyl transfer from chloromethane to a corrin moiety. CmuA was purified from wild-type M. chloromethanicum strain CM4 and characterized as a monomeric, cobalt-containing and zinc-containing enzyme of molecular mass 67 kDa with a bound vitamin B12 cofactor. In combination, CmuA and CmuB proteins catalyze the in vitro transfer of the methyl group of chloromethane to tetrahydrofolate, thus affording a direct link between chloromethane dehalogenation and core C1 metabolism of Methylobacterium. Chloromethane dehalogenase activity in vitro is limited by CmuB, as formation of methyltetrahydrofolate from chloromethane displays apparent Michaelis-Menten kinetics with respect to methylated CmuA, with an apparent Km of 0.27 microM and a Vmax of 0.45 U x mg(-1). This contrasts with sequence-related systems for methyl transfer from methanogens, which involve methyltransferase and corrinoid protein components in well-defined stoichiometric ratios.
- Published
- 2001