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Abstract
Particulate methane monooxygenase (pMMO) is a multi-subunit membrane metalloenzyme used by methanotrophic bacteria to convert methane to methanol. A major hurdle to studying pMMO is the lack of a recombinant expression system, precluding investigation of individual residues by mutagenesis and hampering a complete understanding of its mechanism. Here, we developed an Escherichia coli lysate-based cell-free protein synthesis (CFPS) system that can be used to express pMMO in vitro in the presence of nanodiscs. We used a SUMO fusion construct to generate the native PmoB subunit and showed that the SUMO protease (Ulp1) cleaves the protein in the reaction mixture. Using an affinity tag to isolate the complete pMMO complex, we demonstrated that the complex forms without the need for exogenous translocon machinery or chaperones, confirmed by negative stain electron microscopy. This work demonstrates the potential for using CFPS to express multi-subunit membrane-bound metalloenzymes directly into lipid bilayers.
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Affiliation(s)
- Christopher W. Koo
- Department of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Jasmine M. Hershewe
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - Michael C. Jewett
- Department of Chemical and Biological Engineering and Center for Synthetic Biology, Northwestern University, Evanston, Illinois 60208, United States
| | - Amy C. Rosenzweig
- Department of Molecular Biosciences and of Chemistry and Center for Synthetic Biology, Northwestern University, Evanston, Illinois 60208, United States
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Guo K, Hakobyan A, Glatter T, Paczia N, Liesack W. Methylocystis sp. Strain SC2 Acclimatizes to Increasing NH(4)(+) Levels by a Precise Rebalancing of Enzymes and Osmolyte Composition. mSystems 2022; 7:e0040322. [PMID: 36154142 DOI: 10.1128/msystems.00403-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
A high NH4+ load is known to inhibit bacterial methane oxidation. This is due to a competition between CH4 and NH3 for the active site of particulate methane monooxygenase (pMMO), which converts CH4 to CH3OH. Here, we combined global proteomics with amino acid profiling and nitrogen oxides measurements to elucidate the cellular acclimatization response of Methylocystis sp. strain SC2 to high NH4+ levels. Relative to 1 mM NH4+, a high (50 mM and 75 mM) NH4+ load under CH4-replete conditions significantly increased the lag phase duration required for proteome adjustment. The number of differentially regulated proteins was highly significantly correlated with an increasing NH4+ load. The cellular responses to increasing ionic and osmotic stress involved a significant upregulation of stress-responsive proteins, the K+ "salt-in" strategy, the synthesis of compatible solutes (glutamate and proline), and the induction of the glutathione metabolism pathway. A significant increase in the apparent Km value for CH4 oxidation during the growth phase was indicative of increased pMMO-based oxidation of NH3 to toxic hydroxylamine. The detoxifying activity of hydroxlyamine oxidoreductase (HAO) led to a significant accumulation of NO2- and, upon decreasing O2 tension, N2O. Nitric oxide reductase and hybrid cluster proteins (Hcps) were the candidate enzymes for the production of N2O. In summary, strain SC2 has the capacity to precisely rebalance enzymes and osmolyte composition in response to increasing NH4+ exposure, but the need to simultaneously combat both ionic-osmotic stress and the toxic effects of hydroxylamine may be the reason why its acclimatization capacity is limited to 75 mM NH4+. IMPORTANCE In addition to reducing CH4 emissions from wetlands and landfills, the activity of alphaproteobacterial methane oxidizers of the genus Methylocystis contributes to the sink capacity of forest and grassland soils for atmospheric methane. The methane-oxidizing activity of Methylocystis spp. is, however, sensitive to high NH4+ concentrations. This is due to the competition of CH4 and NH3 for the active site of particulate methane monooxygenase, thereby resulting in the production of toxic hydroxylamine with an increasing NH4+ load. An understanding of the physiological and molecular response mechanisms of Methylocystis spp. is therefore of great importance. Here, we combined global proteomics with amino acid profiling and NOx measurements to disentangle the cellular mechanisms underlying the acclimatization of Methylocystis sp. strain SC2 to an increasing NH4+ load.
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Xin JY, Sun LR, Lin HY, Zhang S, Xia CG. Hybridization of Particulate Methane Monooxygenase by Methanobactin-Modified AuNPs. Molecules 2019; 24:E4027. [PMID: 31703299 PMCID: PMC6891627 DOI: 10.3390/molecules24224027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 10/28/2019] [Accepted: 11/05/2019] [Indexed: 11/16/2022] Open
Abstract
Particulate methane monooxygenase (pMMO) is a characteristic membrane-bound metalloenzyme of methane-oxidizing bacteria that can catalyze the bioconversion of methane to methanol. However, in order to achieve pMMO-based continuous methane-to-methanol bioconversion, the problems of reducing power in vitro regeneration and pMMO stability need to be overcome. Methanobactin (Mb) is a small copper-chelating molecule that functions not only as electron carrier for pMMO catalysis and pMMO protector against oxygen radicals, but also as an agent for copper acquisition and uptake. In order to improve the activity and stability of pMMO, methanobactin-Cu (Mb-Cu)-modified gold nanoparticle (AuNP)-pMMO nanobiohybrids were straightforwardly synthesized via in situ reduction of HAuCl4 to AuNPs in a membrane fraction before further association with Mb-Cu. Mb-Cu modification can greatly improve the activity and stability of pMMO in the AuNP-pMMO nanobiohybrids. It is shown that the Mb-Cu-modified AuNP-pMMO nanobiohybrids can persistently catalyze the conversion of methane to methanol with hydroquinone as electron donor. The artificial heterogeneous nanobiohybrids exhibited excellent reusability and reproducibility in three cycles of catalysis, and they provide a model for achieving hydroquinone-driven conversion of methane to methanol.
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Affiliation(s)
- Jia-Ying Xin
- Key Laboratory of Food Science and Engineering, Harbin University of Commerce, Harbin 150076, China
- State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
| | - Li-Rui Sun
- Key Laboratory of Food Science and Engineering, Harbin University of Commerce, Harbin 150076, China
| | - Hui-Ying Lin
- Key Laboratory of Food Science and Engineering, Harbin University of Commerce, Harbin 150076, China
| | - Shuai Zhang
- Key Laboratory of Food Science and Engineering, Harbin University of Commerce, Harbin 150076, China
| | - Chun-Gu Xia
- State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
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Ro SY, Ross MO, Deng YW, Batelu S, Lawton TJ, Hurley JD, Stemmler TL, Hoffman BM, Rosenzweig AC. From micelles to bicelles: Effect of the membrane on particulate methane monooxygenase activity. J Biol Chem 2018; 293:10457-10465. [PMID: 29739854 DOI: 10.1074/jbc.ra118.003348] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2018] [Revised: 05/06/2018] [Indexed: 11/06/2022] Open
Abstract
Particulate methane monooxygenase (pMMO) is a copper-dependent integral membrane metalloenzyme that converts methane to methanol in methanotrophic bacteria. Studies of isolated pMMO have been hindered by loss of enzymatic activity upon its removal from the native membrane. To characterize pMMO in a membrane-like environment, we reconstituted pMMOs from Methylococcus (Mcc.) capsulatus (Bath) and Methylomicrobium (Mm.) alcaliphilum 20Z into bicelles. Reconstitution into bicelles recovers methane oxidation activity lost upon detergent solubilization and purification without substantial alterations to copper content or copper electronic structure, as observed by electron paramagnetic resonance (EPR) spectroscopy. These findings suggest that loss of pMMO activity upon isolation is due to removal from the membranes rather than caused by loss of the catalytic copper ions. A 2.7 Å resolution crystal structure of pMMO from Mm. alcaliphilum 20Z reveals a mononuclear copper center in the PmoB subunit and indicates that the transmembrane PmoC subunit may be conformationally flexible. Finally, results from extended X-ray absorption fine structure (EXAFS) analysis of pMMO from Mm. alcaliphilum 20Z were consistent with the observed monocopper center in the PmoB subunit. These results underscore the importance of studying membrane proteins in a membrane-like environment and provide valuable insight into pMMO function.
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Affiliation(s)
- Soo Y Ro
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Matthew O Ross
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Yue Wen Deng
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Sharon Batelu
- the Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48201
| | - Thomas J Lawton
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Joseph D Hurley
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Timothy L Stemmler
- the Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48201
| | - Brian M Hoffman
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
| | - Amy C Rosenzweig
- From the Departments of Molecular Biosciences and Chemistry, Northwestern University, Evanston, Illinois 60208 and
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Cao L, Caldararu O, Rosenzweig AC, Ryde U. Quantum Refinement Does Not Support Dinuclear Copper Sites in Crystal Structures of Particulate Methane Monooxygenase. Angew Chem Int Ed Engl 2018; 57:162-166. [PMID: 29164769 PMCID: PMC5808928 DOI: 10.1002/anie.201708977] [Citation(s) in RCA: 94] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 11/06/2017] [Indexed: 01/23/2023]
Abstract
Particulate methane monooxygenase (pMMO) is one of the few enzymes that can activate methane. The metal content of this enzyme has been highly controversial, with suggestions of a dinuclear Fe site or mono-, di-, or trinuclear Cu sites. Crystal structures have shown a mono- or dinuclear Cu site, but the resolution was low and the geometry of the dinuclear site unusual. We have employed quantum refinement (crystallographic refinement enhanced with quantum-mechanical calculations) to improve the structure of the active site. We compared a number of different mono- and dinuclear geometries, in some cases enhanced with more protein ligands or one or two water molecules, to determine which structure fits two sets of crystallographic raw data best. In all cases, the best results were obtained with mononuclear Cu sites, occasionally with an extra water molecule. Thus, we conclude that there is no crystallographic support for a dinuclear Cu site in pMMO.
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Affiliation(s)
- Lili Cao
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, 22100, Lund, Sweden
| | - Octav Caldararu
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, 22100, Lund, Sweden
| | - Amy C Rosenzweig
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, IL, 60208, USA
| | - Ulf Ryde
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, 22100, Lund, Sweden
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Martineau C, Pan Y, Bodrossy L, Yergeau E, Whyte LG, Greer CW. Atmospheric methane oxidizers are present and active in Canadian high Arctic soils. FEMS Microbiol Ecol 2014; 89:257-69. [PMID: 24450397 DOI: 10.1111/1574-6941.12287] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 01/16/2014] [Accepted: 01/16/2014] [Indexed: 01/08/2023] Open
Abstract
The melting of permafrost and the associated potential for methane emissions to the atmosphere are major concerns in the context of global warming. However, soils can also represent a significant sink for methane through the activity of methane-oxidizing bacteria (MOB). In this study, we looked at the activity, diversity, and community structure of MOB at two sampling depths within the active layer in three soils from the Canadian high Arctic. These soils had the capacity to oxidize methane at low (15 ppm) and high (1000 ppm) methane concentrations, but rates differed greatly depending on the sampling date, depth, and site. The pmoA gene sequences related to two genotypes of uncultured MOB involved in atmospheric methane oxidation, the 'upland soil cluster gamma' and the 'upland soil cluster alpha', were detected in soils with near neutral and acidic pH, respectively. Other groups of MOB, including Type I methanotrophs and the 'Cluster 1' genotype, were also detected, indicating a broader diversity of MOB than previously reported for Arctic soils. Overall, the results reported here showed that methane oxidation at both low and high methane concentrations occurs in high Arctic soils and revealed that different groups of atmospheric MOB inhabit these soils.
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Ramakrishnan V, Ogram AV, Lindner AS. Impacts of co-solvent flushing on microbial populations capable of degrading trichloroethylene. Environ Health Perspect 2005; 113:55-61. [PMID: 15626648 PMCID: PMC1253710 DOI: 10.1289/ehp.6937] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
With increased application of co-solvent flushing technologies for removal of nonaqueous phase liquids from groundwater aquifers, concern over the effects of the solvent on native microorganisms and their ability to degrade residual contaminant has also arisen. This study assessed the impact of ethanol flushing on the numbers and activity potentials of trichloroethylene (TCE)-degrading microbial populations present in aquifer soils taken immediately after and 2 years after ethanol flushing of a former dry cleaners site. Polymerase chain reaction analysis revealed soluble methane monooxygenase genes in methanotrophic enrichments, and 16S rRNA analysis identified Methylocystis parvus with 98% similarity, further indicating the presence of a type II methanotroph. Dissimilatory sulfite reductase genes in sulfate-reducing enrichments prepared were also observed. Ethanol flushing was simulated in columns packed with uncontaminated soils from the dry cleaners site that were dosed with TCE at concentrations observed in the field; after flushing, the columns were subjected to a continuous flow of 500 pore volumes of groundwater per week. Total acridine orange direct cell counts of the flushed and nonflushed soils decreased over the 15-week testing period, but after 5 weeks, the flushed soils maintained higher cell counts than the nonflushed soils. Inhibition of methanogenesis by sulfate reduction was observed in all column soils, as was increasing removal of total methane by soils incubated under methanotrophic conditions. These results showed that impacts of ethanol were not as severe as anticipated and imply that ethanol may mitigate the toxicity of TCE to the microorganisms.
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