title: Chloromethane: tetrahydrofolate methyl transfer by two proteins from Methylobacterium chloromethanicum strain CM4.
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.
authors.affiliation: Institut für Mikrobiologie, ETH-Zentrum, Zürich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Studer
authors.forename: E
authors.initials: E
authors.lastname: Stupperich
authors.forename: S
authors.initials: S
authors.lastname: Vuilleumier
authors.forename: T
authors.initials: T
authors.lastname: Leisinger
mesh_terms: D001426:Bacterial Proteins; D002244:Carbon / Q000378:metabolism; D002384:Catalysis; D002474:Cell-Free System; D003035:Cobalt / Q000737:chemistry / Q000494:pharmacology; D005492:Folic Acid / Q000737:chemistry; D007700:Kinetics; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D008737:Methyl Chloride / Q000737:chemistry*; D020580:Methylobacterium / Q000737:chemistry*; D008780:Methyltransferases / Q000737:chemistry* / Q000302:isolation & purification; D008954:Models, Biological; D017434:Protein Structure, Tertiary; D013763:Tetrahydrofolates / Q000737:chemistry*; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D013763:Tetrahydrofolates; D003035:Cobalt; C030371:5,6,7,8-tetrahydrofolic acid; D002244:Carbon; D005492:Folic Acid; D008737:Methyl Chloride; C118740:CmuA protein, Methylobacterium chloromethanicum; D008780:Methyltransferases; D008190:Lyases; C045224:dichloromethane dehalogenase