Oxidation of methane by a biological dicopper centre

• Published in: Nature (London) Vol. 465; no. 7294; pp. 115 - 119
• Main Authors: Balasubramanian, Ramakrishnan, Smith, Stephen M., Rawat, Swati, Yatsunyk, Liliya A., Stemmler, Timothy L., Rosenzweig, Amy C.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.05.2010; Nature Publishing Group
• Subjects: 631/92/173; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Catalytic Domain; Copper; Copper - chemistry; E coli; Enzymes; Enzymes and enzyme inhibitors; Fourier transforms; Fundamental and applied biological sciences. Psychology; Genetic code; High temperature; Humanities and Social Sciences; letter; Methane; Methane - metabolism; Methanol - chemistry; Methylococcus capsulatus - enzymology; Methylosinus trichosporium - enzymology; Models, Molecular; multidisciplinary; Mutation; Oxidation; Oxidation-Reduction; Oxidation-reduction reaction; Oxidoreductases; Oxygenases - chemistry; Oxygenases - genetics; Oxygenases - metabolism; Protein Structure, Tertiary; Proteins; Science; Science (multidisciplinary); Spectrum analysis; Zinc; Methane; Methanotrophy; Enzyme; Active site; Group IB metal; Alkane; Fuel; Prokaryote; Bacteria; Methane monooxygenase; Oxidation; Microorganism; Oxidoreductases; Copper
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature08992

Copper-dependent methane monooxygenase Particulate methane monooxygenase (pMMO) is an integral membrane protein that can selectively oxidize methane to methanol. This metalloenzyme contains three subunits, and the metal composition and exact location of the active site of this enzyme has been the subject of much speculation and controversy. In this paper, the authors determined that the pMMO activity is dependent on copper and not — as has been suggested elsewhere — iron. They also determine that the copper active site is located in the soluble domains of the pmoB subunit, not within the membrane portion of the protein. Particulate methane monooxygenase (pMMO) is an integral membrane protein, found in methanotropic bacteria, that can selectively oxidize methane to produce methanol. This metalloenzyme contains three subunits, and the metal composition and exact location of its active site has been the subject of much speculation. Here it is found that the enzyme's activity is dependent on copper, and that the active site is located in the soluble domains of the pmoB subunit. Vast world reserves of methane gas are underutilized as a feedstock for the production of liquid fuels and chemicals owing to the lack of economical and sustainable strategies for the selective oxidation of methane to methanol 1 . Current processes to activate the strong C–H bond (104 kcal mol -1 ) in methane require high temperatures, are costly and inefficient, and produce waste 2 . In nature, methanotrophic bacteria perform this reaction under ambient conditions using metalloenzymes called methane monooxygenases (MMOs). MMOs thus provide the optimal model for an efficient, environmentally sound catalyst 3 . There are two types of MMO. Soluble MMO (sMMO) is expressed by several strains of methanotroph under copper-limited conditions and oxidizes methane with a well-characterized catalytic di-iron centre 4 . Particulate MMO (pMMO) is an integral membrane metalloenzyme produced by all methanotrophs and is composed of three subunits, pmoA, pmoB and pmoC, arranged in a trimeric α 3 β 3 γ 3 complex 5 . Despite 20 years of research and the availability of two crystal structures, the metal composition and location of the pMMO metal active site are not known. Here we show that pMMO activity is dependent on copper, not iron, and that the copper active site is located in the soluble domains of the pmoB subunit rather than within the membrane. Recombinant soluble fragments of pmoB (spmoB) bind copper and have propylene and methane oxidation activities. Disruption of each copper centre in spmoB by mutagenesis indicates that the active site is a dicopper centre. These findings help resolve the pMMO controversy and provide a promising new approach to developing environmentally friendly C–H oxidation catalysts.