Particulate methane monooxygenase contains only mononuclear copper centers

Abstract

Bacteria that oxidize methane to methanol are central to mitigating emissions of methane, a potent greenhouse gas. The nature of the copper active site in the primary metabolic enzyme of these bacteria, particulate methane monooxygenase (pMMO), has been controversial owing to seemingly contradictory biochemical, spectroscopic, and crystallographic results. We present biochemical and electron paramagnetic resonance spectroscopic characterization most consistent with two monocopper sites within pMMO: one in the soluble PmoB subunit at the previously assigned active site (CuB) and one ~2 nanometers away in the membrane-bound PmoC subunit (CuC). On the basis of these results, we propose that a monocopper site is able to catalyze methane oxidation in pMMO.

Bioinspired chemistry at MOF secondary building units

“…10 Oxo-bridged copper centers have been proposed (but recently called into question, vide infra) as intermediates in the oxidation of methane to methanol by pMMO. 42 Sequential isothermal treatments of 3% N 2 O in He followed by ow of CH 4 for one hour at 150 C resulted in the formation of methanol with productivities ranging from $1.5-2.5 mmol MeOH per mol Cu dependent on the imidazole ligand (Table 1), with no loss of MOF crystallinity. A Cu 2 O 2 active site proposed from density functional theory (DFT) was supported by X-ray absorption spectroscopy.…”

“…40 Leading structural proposals for the active sites invoke mono or dinuclear copper centers in pMMO, and dinuclear iron sites in sMMO. [41][42][43] These motifs are found in a variety of Cu/Fe MOF SBUs and have accordingly been investigated for methane/ ethane oxidation activity. Other examples of alkane oxidation by abiological metals and/or oxidizing metal species (e.g.…”

Approaches for Selective Oxidation of Methane to Methanol

“…In comparison to the iron based active centers in sMMO, pMMO contains a catalytic copper center [13,35]. In a recent report, Ross et al [36] reported that pMMO consists of two mono-copper active sites, having an assembly of protein sub-units, PmoB and PmoC, for methane binding and oxidation [36]. According to their study, methane oxidation to methanol in pMMO occurs in the presence of an electron donor, formaldehyde dehydrogenase (FADH), which generates hydrogen peroxide (H 2 O 2 ) at the PmoB site.…”

Large Freshwater Phages with the Potential to Augment Aerobic Methane Oxidation

“…2a, Supplementary Fig. 9 ) 9 and required for O 2 binding and methane oxidation 26 . Interestingly, the bacterial and phage-associated PmoC sequences were generally very similar in the central membrane-and periplasmic associated portions, but divergent at the cytoplasmic N-and C-termini.…”

“…Although possibly acquired from bacterial hosts along with other genes, only pmoC was retained as it can enhance phage fitness alone. In bacterial methanotrophs, there is increasing evidence indicating the essential role of PmoC in methane oxidation and the absolute necessity of PmoB is questionable 12,25,26,40 . Given that the structure of PmoC is susceptible and largely disordered when the cell membrane is perturbed 41 , we suggest that the additional pmoC genes either in the bacterial methanotroph or phage genome ( Supplementary Table 3 ) could sustain methane oxidation under abnormal conditions.…”