Catalytic and Spectroscopic Properties of the Halotolerant Soluble Methane Monooxygenase Reductase from Methylomonas methanica MC09.
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ABSTRACT:
SUBMITTER: Lettau E
PROVIDER: S-EPMC9305295 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The soluble MMO (sMMO) gene clusters from group I methanotrophs were characterized. An 8.1-kb KpnI fragment from Methylomonas sp. strain KSWIII and a 7.5-kb SalI fragment from Methylomonas sp. strain KSPIII which contained the sMMO gene clusters were cloned and sequenced. The sequences of these two fragments were almost identical. The sMMO gene clusters in the fragment consisted of six open reading frames which were 52 to 79% similar to the corresponding genes of previously described sMMO gene clusters of the group II and group X methanotrophs. The phylogenetic analysis of the predicted amino acid sequences of sMMO demonstrated that the sMMOs from these strains were closer to that from M. capsulatus Bath in the group X methanotrophs than to those from Methylosinus trichosporium OB3b and Methylocystis sp. strain M in the group II methanotrophs. Based on the sequence data of sMMO genes of our strains and other methanotrophs, we designed a new PCR primer to amplify sMMO gene fragments of all the known methanotrophs harboring the mmoX gene. The primer set was successfully used for detecting methanotrophs in the groundwater of trichloroethylene-contaminated sites during in situ-biostimulation treatments.
| S-EPMC91705 | biostudies-literature
Project description:The controlled oxidation of methane to methanol is a chemical transformation of great value, particularly in the pursuit of alternative fuels, but the reaction remains underutilized industrially because of inefficient and costly synthetic procedures. In contrast, methane monooxygenase enzymes (MMOs) from methanotrophic bacteria achieve this chemistry efficiently under ambient conditions. In this Account, we discuss the first observable step in the oxidation of methane at the carboxylate-bridged diiron active site of the soluble MMO (sMMO), namely, the reductive activation of atmospheric O(2). The results provide benchmarks against which the dioxygen activation mechanisms of other bacterial multicomponent monooxygenases can be measured. Molecular oxygen reacts rapidly with the reduced diiron(II) cen-ter of the hydroxylase component of sMMO (MMOH). The first spectroscopically characterized intermediate that results from this process is a peroxodiiron(III) species, P*, in which the iron atoms have identical environments. P* converts to a second peroxodiiron(III) unit, H(peroxo), in a process accompanied by the transfer of a proton, probably with the assistance of a residue near the active site. Proton-promoted O-O bond scission and rearrangement of the diiron core then leads to a diiron(IV) unit, termed Q, that is directly responsible for the oxidation of methane to methanol. In one section of this Account, we provide a detailed discussion of these processes, with particular emphasis on possible structures of the intermediates. The geometries of P* and H(peroxo) are currently unknown, and recent synthetic modeling chemistry has highlighted the need for further structural characterization of Q, currently assigned as a di(μ-oxo)diiron(IV) "diamond core." In another section of the Account, we discuss in detail proton transfer during the O(2) activation events. The role of protons in promoting O-O bond cleavage, thereby initiating the conversion of H(peroxo) to Q, was previously a controversial topic. Recent studies of the mechanism, covering a range of pH values and in D(2)O instead of H(2)O, confirmed conclusively that the transfer of protons, possibly at or near the active site, is necessary for both P*-to-H(peroxo) and H(peroxo)-to-Q conversions. Specific mechanistic insights into these processes are provided. In the final section of the Account, we present our view of experiments that need to be done to further define crucial aspects of sMMO chemistry. Here our goal is to detail the challenges that we and others face in this research, particularly with respect to some long-standing questions about the system, as well as approaches that might be used to solve them.
| S-EPMC3079780 | biostudies-literature
Project description:The hydroxylation or epoxidation of hydrocarbons by bacterial multicomponent monooxygenases (BMMs) requires the interplay of three or four protein components. How component protein interactions control catalysis, however, is not well understood. In particular, the binding sites of the reductase components on the surface of their cognate hydroxylases and the role(s) that the regulatory proteins play during intermolecular electron transfer leading to the hydroxylase reduction have been enigmatic. Here we determine the reductase binding site on the hydroxylase of a BMM enzyme, soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). We present evidence that the ferredoxin domain of the reductase binds to the canyon region of the hydroxylase, previously determined to be the regulatory protein binding site as well. The latter thus inhibits reductase binding to the hydroxylase and, consequently, intermolecular electron transfer from the reductase to the hydroxylase diiron active site. The binding competition between the regulatory protein and the reductase may serve as a control mechanism for regulating electron transfer, and other BMM enzymes are likely to adopt the same mechanism.
| S-EPMC4105053 | biostudies-literature
Project description:The soluble methane monooxygenase (sMMO; EC 1.14.13.25) from the pseudothermophile Methylococcus capsulatus (Bath) is a three-component enzyme system that catalyzes the selective oxidation of methane to methanol. We have used NMR spectroscopy to produce a highly refined structure of MMOB, the 16-kDa regulatory protein of this system. This structure has a unique and intricate fold containing seven beta-strands forming two beta-sheets oriented perpendicular to each other and bridged by three alpha-helices. The rate and efficiency of the methane hydroxylation by sMMO depend on dynamic binding interactions of the hydroxylase with the reductase and regulatory protein components during catalysis. We have monitored by NMR the binding of MMOB to the hydroxylase in the presence and absence of the reductase. The results of these studies provide structural insight into how the regulatory protein interacts with the hydroxylase.
| S-EPMC22155 | biostudies-literature
Project description:During a single turnover of the hydroxylase component (MMOH) of soluble methane monooxygenase from Methylosinus trichosporium OB3b, several discrete intermediates are formed. The diiron cluster of MMOH is first reduced to the Fe(II)Fe(II) state (H(red)). O₂ binds rapidly at a site away from the cluster to form the Fe(II)Fe(II) intermediate O, which converts to an Fe(III)Fe(III)-peroxo intermediate P and finally to the Fe(IV)Fe(IV) intermediate Q. Q binds and reacts with methane to yield methanol and water. The rate constants for these steps are increased by a regulatory protein, MMOB. Previously reported transient kinetic studies have suggested that an intermediate P* forms between O and P in which the g = 16 EPR signal characteristic of the reduced diiron cluster of H(red) and O is lost. This was interpreted as signaling oxidation of the cluster, but a low level of accumulation of P* prevented further characterization. In this study, three methods for directly detecting and trapping P* are applied together to allow its spectroscopic and kinetic characterization. First, the MMOB mutant His33Ala is used to specifically slow the decay of P* without affecting its formation rate, leading to its nearly quantitative accumulation. Second, spectra-kinetic data collection is used to provide a sensitive measure of the formation and decay rate constants of intermediates as well as their optical spectra. Finally, the substrate furan is included to react with Q and quench its strong chromophore. The optical spectrum of P* closely mimics those of H(red) and O, but it is distinctly different from that of P. The reaction cycle rate constants allowed prediction of the times for maximal accumulation of the intermediates. Mössbauer spectra of rapid freeze-quench samples at these times show that the intermediates are formed at almost exactly the predicted levels. The Mössbauer spectra show that the diiron cluster of P*, quite unexpectedly, is in the Fe(II)Fe(II) state. Thus, the loss of the g = 16 EPR signal results from a change in the electronic structure of the Fe(II)Fe(II) center rather than oxidation. The similarity of the optical and Mössbauer spectra of H(red), O, and P* suggests that only subtle changes occur in the electronic and physical structure of the diiron cluster as P* forms. Nevertheless, the changes that do occur are necessary for O₂ to be activated for hydrocarbon oxidation.
| S-EPMC3712755 | biostudies-literature
Project description:Soluble methane monooxygenase in methanotrophs converts methane to methanol under ambient conditions. The maximum catalytic activity of hydroxylase (MMOH) is achieved through the interplay of its regulatory protein (MMOB) and reductase. An additional auxiliary protein, MMOD, functions as an inhibitor of MMOH; however, its inhibitory mechanism remains unknown. Here, we report the crystal structure of the MMOH-MMOD complex from Methylosinus sporium strain 5 (2.6 Å). Its structure illustrates that MMOD associates with the canyon region of MMOH where MMOB binds. Although MMOD and MMOB recognize the same binding site, each binding component triggers different conformational changes toward MMOH, which then respectively lead to the inhibition and activation of MMOH. Particularly, MMOD binding perturbs the di-iron geometry by inducing two major MMOH conformational changes, i.e., MMOH β subunit disorganization and subsequent His147 dissociation with Fe1 coordination. Furthermore, 1,6-hexanediol, a mimic of the products of sMMO, reveals the substrate access route.
| S-EPMC6774732 | biostudies-literature
Project description:The hydroxylation of methane (CH4) is crucial to the field of environmental microbiology, owing to the heat capacity of methane, which is much higher than that of carbon dioxide (CO2). Soluble methane monooxygenase (sMMO), a member of the bacterial multicomponent monooxygenase (BMM) superfamily, is essential for the hydroxylation of specific substrates, including hydroxylase (MMOH), regulatory component (MMOB), and reductase (MMOR). The diiron active site positioned in the MMOH α-subunit is reduced through the interaction of MMOR in the catalytic cycle. The electron transfer pathway, however, is not yet fully understood due to the absence of complex structures with reductases. A type II methanotroph, Methylosinus sporium 5, successfully expressed sMMO and hydroxylase, which were purified for the study of the mechanisms. Studies on the MMOH-MMOB interaction have demonstrated that Tyr76 and Trp78 induce hydrophobic interactions through π-π stacking. Structural analysis and sequencing of the ferredoxin domain in MMOR (MMOR-Fd) suggested that Tyr93 and Tyr95 could be key residues for electron transfer. Mutational studies of these residues have shown that the concentrations of flavin adenine dinucleotide (FAD) and iron ions are changed. The measurements of dissociation constants (Kds) between hydroxylase and mutated reductases confirmed that the binding affinities were not significantly changed, although the specific enzyme activities were significantly reduced by MMOR-Y93A. This result shows that Tyr93 could be a crucial residue for the electron transfer route at the interface between hydroxylase and reductase.
| S-EPMC9628860 | biostudies-literature
Project description:Soluble methane monooxygenase (sMMO) is a multicomponent metalloenzyme capable of catalyzing the fissure of the C-H bond of methane and the insertion of one atom of oxygen from O2 to yield methanol. Efficient multiple-turnover catalysis occurs only in the presence of all three sMMO protein components: hydroxylase (MMOH), reductase (MMOR), and regulatory protein (MMOB). The complex series of sMMO protein component interactions that regulate the formation and decay of sMMO reaction cycle intermediates is not fully understood. Here, the two tryptophan residues in MMOB and the single tryptophan residue in MMOR are converted to 5-fluorotryptophan (5FW) by expression in defined media containing 5-fluoroindole. In addition, the mechanistically significant N-terminal region of MMOB is 19F-labeled by reaction of the K15C variant with 3-bromo-1,1,1-trifluoroacetone (BTFA). The 5FW and BTFA modifications cause minimal structural perturbation, allowing detailed studies of the interactions with sMMOH using 19F NMR. Resonances from the 275 kDa complexes of sMMOH with 5FW-MMOB and BTFA-K15C-5FW-MMOB are readily detected at 5 μM labeled protein concentration. This approach shows directly that MMOR and MMOB competitively bind to sMMOH with similar KD values, independent of the oxidation state of the sMMOH diiron cluster. These findings suggest a new model for regulation in which the dynamic equilibration of MMOR and MMOB with sMMOH allows a transient formation of key reactive complexes that irreversibly pull the reaction cycle forward. The slow kinetics of exchange of the sMMOH:MMOB complex is proposed to prevent MMOR-mediated reductive quenching of the high-valent reaction cycle intermediate Q before it can react with methane.
| S-EPMC8345336 | biostudies-literature
Project description:Methane oxidation by aerobic methanotrophs is well-known to be strongly regulated by the availability of copper, i.e., the “copper-switch”. That is, there are two forms of the methane monooxygenase: a cytoplasmic or soluble methane monooxygenase (sMMO) and a membrane-bound or particulate methane monooxygenase (pMMO). sMMO is only expressed and active in the absence of copper, while pMMO requires copper. Previous work has also shown that one gene in the operon of the soluble methane monooxygenase – mmoD – also plays a critical role, but its function is still vague. Herein we show that MmoD is not needed for expression of genes in the sMMO gene cluster but is critical for formation of sMMO polypeptides and sMMO activity in Methylosinus trichosporium OB3b, indicating that MmoD plays a key post-transcriptional role in maturation of sMMO. Further, data also show that MmoD controls expression of methanobactin, a unique copper-binding compound used by some methanotrophs for copper collection. Collectively these results provide greater insights into the components of the “copper-switch” and thus provide new strategies to manipulate methanotrophic activity.
2023-09-29 | PXD045741 | Pride
Project description:Methanotrophs with soluble methane monooxygenase (sMMO) show high potential for various ecological and biotechnological applications. Here, we developed a high throughput method to identify sMMO-producing microbes by integrating droplet microfluidics and a genetic circuit-based biosensor system. sMMO-producers and sensor cells were encapsulated in monodispersed droplets with benzene as the substrate and incubated for 5 h. The sensor cells were analyzed as the reporter for phenol-sensitive transcription activation of fluorescence. Various combinations of methanotrophs and biosensor cells were investigated to optimize the performance of our droplet-integrated transcriptional factor biosensor system. As a result, the conditions to ensure sMMO activity to convert the starting material, benzene, into phenol, were determined. The biosensor signals were sensitive and quantitative under optimal conditions, showing that phenol is metabolically stable within both cell species and accumulates in picoliter-sized droplets, and the biosensor cells are healthy enough to respond quantitatively to the phenol produced. These results show that our system would be useful for rapid evaluation of phenotypes of methanotrophs showing sMMO activity, while minimizing the necessity of time-consuming cultivation and enzyme preparation, which are required for conventional analysis of sMMO activity.
| S-EPMC7193049 | biostudies-literature