MetaCyc Polypeptide: soluble methane monooxygenase reductase component

Gene: mmoC Accession Number: G-2930 (MetaCyc)

Species: Methylosinus trichosporium OB3b

Component of: soluble methane monooxygenase (extended summary available)

The reductase component of the soluble methane monooxygenase (MMOR) is an iron-sulfur flavoprotein, whose main responsibility is to shuttle electrons from NADH through its FAD and [2Fe-2S] cofactors to the hydroxylase active site [Lund85, Lund85a].

Gene Citations: [Cardy91]

Molecular Weight of Polypeptide: 39.7 kD (experimental) [Fox89]

Unification Links: ModBase:Q53563, Protein Model Portal:Q53563, Swiss-Model:Q53563, UniProt:Q53563

Relationship Links: Entrez-Nucleotide:RELATED-TO:X55394, InterPro:IN-FAMILY:IPR001041, InterPro:IN-FAMILY:IPR001221, InterPro:IN-FAMILY:IPR001433, InterPro:IN-FAMILY:IPR001709, InterPro:IN-FAMILY:IPR008333, InterPro:IN-FAMILY:IPR012675, InterPro:IN-FAMILY:IPR017927, InterPro:IN-FAMILY:IPR017938, Pfam:IN-FAMILY:PF00111, Pfam:IN-FAMILY:PF00175, Pfam:IN-FAMILY:PF00970, Prints:IN-FAMILY:PR00371, Prints:IN-FAMILY:PR00410, Prosite:IN-FAMILY:PS51384

Gene-Reaction Schematic

Gene-Reaction Schematic

MultiFun Terms: metabolismcarbon utilizationcarbon compounds

Subunit of: soluble methane monooxygenase

Species: Methylosinus trichosporium OB3b

Subunit composition of soluble methane monooxygenase = [([MmoX][MmoY][MmoZ])2][MmoC][MmoB][OrfY]
         soluble methane monooxygenase hydroxylase component dimer = ([MmoX][MmoY][MmoZ])2 (summary available)
                 soluble methane monooxygenase hydroxylase component monomer = (MmoX)(MmoY)(MmoZ)
                         soluble methane monooxygenase hydroxylase component α subunit = MmoX (summary available)
                         soluble methane monooxygenase hydroxylase component β subunit = MmoY (summary available)
                         soluble methane monooxygenase hydroxylase component γ subunit = MmoZ (summary available)
         soluble methane monooxygenase reductase component = MmoC (summary available)
         soluble methane monooxygenase regulatory component = MmoB (summary available)
         soluble methane monooxygenase MMOD component = OrfY

Almost all methanotrophic bacteria contain a membrane-bound, copper-dependent, particulate form of MMO (pMMO), and some also express a soluble form (sMMO) under conditions of low copper availability. The sMMO proteins are more stable and easier to purify than those of pMMO, and the enzymes from Methylococcus capsulatus Bath and Methylosinus trichosporium OB3b in particular have been studied in considerable detail over the last decade.

Full catalytic activity requires the presence of three protein components. Reductive activation of dioxygen and the oxidation of methane occur at carboxylate-bridged diiron centers in the subunits of the hydroxylase enzyme MMOH, a 251-kDa α2β2γ2 protein. A reductase, MMOR, which contains both a [2Fe-2S] ferredoxin and an FAD (flavine adenine dinucleotide) domain, provides electrons to MMOH by oxidizing NADH to NAD+. Finally, the presence of a small cofactorless protein, MMOB, is required for efficient catalysis [Fox89].

Recent work demonstrated that a fourth protein, MMOD, is also involved in the sMMO system [Merkx02].

Three substrates are involved in the reaction of sMMO. Both O2 and CH4 react at the dinuclear iron centers of MMOH, whereas the third, NADH, reacts at the FAD center of MMOR. Steady-state kinetic data support a catalytic cycle in which the sMMO system reacts sequentially with CH4, NADH, and O2. Initially, methane binds to the oxidized hydroxylase. NADH subsequently transfers a hydride to the FAD moiety of MMOR, and two electrons are transmitted sequentially from the reduced FAD through the [2Fe-2S] center of MMOR to a binuclear non-heme iron cluster(III) center of the hydroxylase by means of intra- and intermolecular electron-transfer reactions. Molecular oxygen then binds to the diiron(II) center of the hydroxylase where it is reductively activated to hydroxylate methane, forming methanol and water [Gassner99].

Enzymatic reaction of: methane monooxygenase

Inferred from experiment

EC Number:

methane + NAD(P)H + oxygen + H+ → methanol + NAD(P)+ + H2O

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: methane oxidation to methanol I

Cofactors or Prosthetic Groups: binuclear non-heme iron cluster


Cardy91: Cardy DL, Laidler V, Salmond GP, Murrell JC (1991). "The methane monooxygenase gene cluster of Methylosinus trichosporium: cloning and sequencing of the mmoC gene." Arch Microbiol 156(6);477-83. PMID: 1785954

Fox89: Fox BG, Froland WA, Dege JE, Lipscomb JD (1989). "Methane monooxygenase from Methylosinus trichosporium OB3b. Purification and properties of a three-component system with high specific activity from a type II methanotroph." J Biol Chem 264(17);10023-33. PMID: 2542319

Gassner99: Gassner GT, Lippard SJ (1999). "Component interactions in the soluble methane monooxygenase system from Methylococcus capsulatus (Bath)." Biochemistry 38(39);12768-85. PMID: 10504247

Lund85: Lund J, Dalton H (1985). "Further characterisation of the FAD and Fe2S2 redox centres of component C, the NADH:acceptor reductase of the soluble methane monooxygenase of Methylococcus capsulatus (Bath)." Eur J Biochem 147(2);291-6. PMID: 2982614

Lund85a: Lund J, Woodland MP, Dalton H (1985). "Electron transfer reactions in the soluble methane monooxygenase of Methylococcus capsulatus (Bath)." Eur J Biochem 147(2);297-305. PMID: 3918864

Merkx02: Merkx M, Lippard SJ (2002). "Why OrfY? Characterization of MMOD, a long overlooked component of the soluble methane monooxygenase from Methylococcus capsulatus (Bath)." J Biol Chem 277(8);5858-65. PMID: 11709550

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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