title: RamA, a protein required for reductive activation of corrinoid-dependent methylamine methyltransferase reactions in methanogenic archaea.
abstract: Archaeal methane formation from methylamines is initiated by distinct methyltransferases with specificity for monomethylamine, dimethylamine, or trimethylamine. Each methylamine methyltransferase methylates a cognate corrinoid protein, which is subsequently demethylated by a second methyltransferase to form methyl-coenzyme M, the direct methane precursor. Methylation of the corrinoid protein requires reduction of the central cobalt to the highly reducing and nucleophilic Co(I) state. RamA, a 60-kDa monomeric iron-sulfur protein, was isolated from Methanosarcina barkeri and is required for in vitro ATP-dependent reductive activation of methylamine:CoM methyl transfer from all three methylamines. In the absence of the methyltransferases, highly purified RamA was shown to mediate the ATP-dependent reductive activation of Co(II) corrinoid to the Co(I) state for the monomethylamine corrinoid protein, MtmC. The ramA gene is located near a cluster of genes required for monomethylamine methyltransferase activity, including MtbA, the methylamine-specific CoM methylase and the pyl operon required for co-translational insertion of pyrrolysine into the active site of methylamine methyltransferases. RamA possesses a C-terminal ferredoxin-like domain capable of binding two tetranuclear iron-sulfur proteins. Mutliple ramA homologs were identified in genomes of methanogenic Archaea, often encoded near methyltrophic methyltransferase genes. RamA homologs are also encoded in a diverse selection of bacterial genomes, often located near genes for corrinoid-dependent methyltransferases. These results suggest that RamA mediates reductive activation of corrinoid proteins and that it is the first functional archetype of COG3894, a family of redox proteins of unknown function.
authors.affiliation: Department of Microbiology and The Ohio State Biochemistry Program, Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Ferguson
authors.forename: Jitesh A
authors.initials: JA
authors.lastname: Soares
authors.forename: Tanja
authors.initials: T
authors.lastname: Lienard
authors.forename: Gerhard
authors.initials: G
authors.lastname: Gottschalk
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Krzycki
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D019843:Archaeal Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D045728:Corrinoids / Q000378:metabolism*; D004789:Enzyme Activation; D005288:Ferredoxins / Q000235:genetics / Q000378:metabolism; D020745:Genome, Archaeal / Q000235:genetics; D017021:Methanosarcina barkeri / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D013997:Time Factors
chemical_list: D019843:Archaeal Proteins; D045728:Corrinoids; D005288:Ferredoxins; D000255:Adenosine Triphosphate; D008780:Methyltransferases