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Huang Y, Huangfu X, Ma C, Liu Z. Sequestration and oxidation of heavy metals mediated by Mn(II) oxidizing microorganisms in the aquatic environment. CHEMOSPHERE 2023; 329:138594. [PMID: 37030347 DOI: 10.1016/j.chemosphere.2023.138594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 03/30/2023] [Accepted: 04/01/2023] [Indexed: 05/03/2023]
Abstract
Microorganisms can oxidize Mn(II) to biogenic Mn oxides (BioMnOx), through enzyme-mediated processes and non-enzyme-mediated processes, which are generally considered as the source and sink of heavy metals due to highly reactive to sequestrate and oxidize heavy metals. Hence, the summary of interactions between Mn(II) oxidizing microorganisms (MnOM) and heavy metals is benefit for further work on microbial-mediated self-purification of water bodies. This review comprehensively summarizes the interactions between MnOM and heavy metals. The processes of BioMnOx production by MnOM has been firstly discussed. Moreover, the interactions between BioMnOx and various heavy metals are critically discussed. On the one hand, modes for heavy metals adsorbed on BioMnOx are summarized, such as electrostatic attraction, oxidative precipitation, ion exchange, surface complexation, and autocatalytic oxidation. On the other hand, adsorption and oxidation of representative heavy metals based on BioMnOx/Mn(II) are also discussed. Thirdly, the interactions between MnOM and heavy metals are also focused on. Finally, several perspectives which will contribute to future research are proposed. This review provides insight into the sequestration and oxidation of heavy metals mediated by Mn(II) oxidizing microorganisms. It might be helpful to understand the geochemical fate of heavy metals in the aquatic environment and the process of microbial-mediated water self-purification.
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Affiliation(s)
- Yuheng Huang
- Key Laboratory of Eco-Environments in Three Gorges Reservoir Region, Ministry of Education, College of Environment, and Ecology, Chongqing University, Chongqing, 400044, China
| | - Xiaoliu Huangfu
- Key Laboratory of Eco-Environments in Three Gorges Reservoir Region, Ministry of Education, College of Environment, and Ecology, Chongqing University, Chongqing, 400044, China.
| | - Chengxue Ma
- State Key Laboratory of Urban Water Resource, and Environment, School of Municipal, and Environmental Engineering, Harbin Institute of Technology, Harbin, 150090, China
| | - Ziqiang Liu
- Key Laboratory of Eco-Environments in Three Gorges Reservoir Region, Ministry of Education, College of Environment, and Ecology, Chongqing University, Chongqing, 400044, China
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2
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Proteins-Based Nanocatalysts for Energy Conversion Reactions. Top Curr Chem (Cham) 2020; 378:43. [PMID: 32562011 DOI: 10.1007/s41061-020-00306-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 06/10/2020] [Indexed: 10/24/2022]
Abstract
In recent years, the incorporation of molecular enzymes into nanostructured frameworks to create efficient energy conversion biomaterials has gained increasing interest as a promising strategy owing to both the dynamic behavior of proteins for their electrocatalytic function and the unique properties of the synergistic interactions between proteins and nanosized materials. Herein, we review the impact of proteins on energy conversion fields and the contribution of proteins to the improved activity of the resulting nanocomposites. We address different strategies to fabricate protein-based nanocatalysts as well as current knowledge on the structure-function relationships of enzymes during the catalytic processes. Additionally, a comprehensive review of state-of-the-art bioelectrocatalytic materials for water-splitting reactions such as hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) is afforded. Finally, we briefly envision opportunities to develop a new generation of electrocatalysts towards the electrochemical reduction of N2 to NH3 using theoretical tools to built nature-inspired nitrogen reduction reaction catalysts.
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Medina M, Rizo A, Dinh D, Chau B, Omidvar M, Juarez A, Ngo J, Johnson HA. MopA, the Mn Oxidizing Protein From Erythrobacter sp. SD-21, Requires Heme and NAD + for Mn(II) Oxidation. Front Microbiol 2018; 9:2671. [PMID: 30487779 PMCID: PMC6247904 DOI: 10.3389/fmicb.2018.02671] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 10/19/2018] [Indexed: 11/15/2022] Open
Abstract
Bacterial manganese (Mn) oxidation is catalyzed by a diverse group of microbes and can affect the fate of other elements in the environment. Yet, we understand little about the enzymes that catalyze this reaction. The Mn oxidizing protein MopA, from Erythrobacter sp. strain SD-21, is a heme peroxidase capable of Mn(II) oxidation. Unlike Mn oxidizing multicopper oxidase enzymes, an understanding of MopA is very limited. Sequence analysis indicates that MopA contains an N-terminal heme peroxidase domain and a C-terminal calcium binding domain. Heterologous expression and nickel affinity chromatography purification of the N-terminal peroxidase domain (MopA-hp) from Erythrobacter sp. strain SD-21 led to partial purification. MopA-hp is a heme binding protein that requires heme, NAD+, and calcium (Ca2+) for activity. Mn oxidation is also stimulated by the presence of pyrroloquinoline quinone. MopA-hp has a KM for Mn(II) of 154 ± 46 μM and kcat = 1.6 min−1. Although oxygen requiring MopA-hp is homologous to peroxidases based on sequence, addition of hydrogen peroxide and hydrogen peroxide scavengers had little effect on Mn oxidation, suggesting this is not the oxidizing agent. These studies provide insight into the mechanism by which MopA oxidizes Mn.
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Affiliation(s)
- Michael Medina
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Antonia Rizo
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - David Dinh
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Briana Chau
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Moussa Omidvar
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Andrew Juarez
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Julia Ngo
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
| | - Hope A Johnson
- Department of Biological Science, Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA, United States
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4
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Tao L, Stich TA, Soldatova AV, Tebo BM, Spiro TG, Casey WH, Britt RD. Mn(III) species formed by the multi-copper oxidase MnxG investigated by electron paramagnetic resonance spectroscopy. J Biol Inorg Chem 2018; 23:1093-1104. [PMID: 29968177 DOI: 10.1007/s00775-018-1587-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 06/22/2018] [Indexed: 01/24/2023]
Abstract
The multi-copper oxidase (MCO) MnxG from marine Bacillus bacteria plays an essential role in geochemical cycling of manganese by oxidizing Mn2+(aq) to form manganese oxide minerals at rates that are three to five orders of magnitude faster than abiotic rates. The MCO MnxG protein is isolated as part of a multi-protein complex, denoted as Mnx, which includes one MnxG unit and a hexamer of MnxE3F3 subunit. During the oxidation of Mn2+(aq) catalyzed by the Mnx protein complex, an enzyme-bound Mn(III) species was trapped recently in the presence of pyrophosphate (PP) and analyzed using parallel-mode electron paramagnetic resonance (EPR) spectroscopy. Herein, we provide a full analysis of this enzyme-bound Mn(III) intermediate via temperature dependence studies and spectral simulations. This Mnx-bound Mn(III) species is characterized by a hyperfine-coupling value of A(55Mn) = 4.2 mT (corresponding to 120 MHz) and a negative zero-field splitting (ZFS) value of D = - 2.0 cm-1. These magnetic properties suggest that the Mnx-bound Mn(III) species could be either six-coordinate with a 5B1g ground state or square-pyramidal five-coordinate with a 5B1 ground state. In addition, as a control, Mn(III)PP is also analyzed by parallel-mode EPR spectroscopy. It exhibits distinctly different magnetic properties with a hyperfine-coupling value of A(55Mn) = 4.8 mT (corresponding to 140 MHz) and a negative ZFS value of D = - 2.5 cm-1. The different ZFS values suggest differences in ligand environment of Mnx-bound Mn(III) and aqueous Mn(III)PP species. These studies provide further insights into the mechanism of biological Mn2+(aq) oxidation.
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Affiliation(s)
- Lizhi Tao
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA, 95616, USA
| | - Troy A Stich
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA, 95616, USA
| | - Alexandra V Soldatova
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195, USA
| | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Oregon Health and Science University, Portland, OR, 97239, USA
| | - Thomas G Spiro
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195, USA
| | - William H Casey
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA, 95616, USA
- Department of Geology, University of California, One Shields Avenue, Davis, CA, 95616, USA
| | - R David Britt
- Department of Chemistry, University of California, One Shields Avenue, Davis, CA, 95616, USA.
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Zhou M, Yan J, Romano CA, Tebo BM, Wysocki VH, Paša-Tolić L. Surface Induced Dissociation Coupled with High Resolution Mass Spectrometry Unveils Heterogeneity of a 211 kDa Multicopper Oxidase Protein Complex. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:723-733. [PMID: 29388167 PMCID: PMC7305857 DOI: 10.1007/s13361-017-1882-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2017] [Revised: 12/22/2017] [Accepted: 12/22/2017] [Indexed: 05/11/2023]
Abstract
Manganese oxidation is an important biogeochemical process that is largely regulated by bacteria through enzymatic reactions. However, the detailed mechanism is poorly understood due to challenges in isolating and characterizing these unknown enzymes. A manganese oxidase, Mnx, from Bacillus sp. PL-12 has been successfully overexpressed in active form as a protein complex with a molecular mass of 211 kDa. We have recently used surface induced dissociation (SID) and ion mobility-mass spectrometry (IM-MS) to release and detect folded subcomplexes for determining subunit connectivity and quaternary structure. The data from the native mass spectrometry experiments led to a plausible structural model of this multicopper oxidase, which has been difficult to study by conventional structural biology methods. It was also revealed that each Mnx subunit binds a variable number of copper ions. Becasue of the heterogeneity of the protein and limited mass resolution, ambiguities in assigning some of the observed peaks remained as a barrier to fully understanding the role of metals and potential unknown ligands in Mnx. In this study, we performed SID in a modified Fourier transform-ion cyclotron resonance (FTICR) mass spectrometer. The high mass accuracy and resolution offered by FTICR unveiled unexpected artificial modifications on the protein that had been previously thought to be iron bound species based on lower resolution spectra. Additionally, isotopically resolved spectra of the released subcomplexes revealed the metal binding stoichiometry at different structural levels. This method holds great potential for in-depth characterization of metalloproteins and protein-ligand complexes. Graphical Abstract ᅟ.
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Affiliation(s)
- Mowei Zhou
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Blvd, Richland, WA, 99354, USA
| | - Jing Yan
- Department of Chemistry and Biochemistry, Ohio State University, 460 W 12th Ave, Columbus, OH, 43210, USA
| | - Christine A Romano
- Division of Environmental and Biomolecular Systems, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR, 97239, USA
| | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR, 97239, USA
| | - Vicki H Wysocki
- Department of Chemistry and Biochemistry, Ohio State University, 460 W 12th Ave, Columbus, OH, 43210, USA
| | - Ljiljana Paša-Tolić
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Blvd, Richland, WA, 99354, USA.
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6
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Zhang C, Shi S. Physiological and Proteomic Responses of Contrasting Alfalfa ( Medicago sativa L.) Varieties to PEG-Induced Osmotic Stress. FRONTIERS IN PLANT SCIENCE 2018; 9:242. [PMID: 29541085 PMCID: PMC5835757 DOI: 10.3389/fpls.2018.00242] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Accepted: 02/12/2018] [Indexed: 05/23/2023]
Abstract
Drought severely limits global plant distribution and agricultural production. Elucidating the physiological and molecular mechanisms governing alfalfa stress responses will contribute to the improvement of drought tolerance in leguminous crops. In this study, the physiological and proteomic responses of two alfalfa (Medicago sativa L.) varieties contrasting in drought tolerance, Longzhong (drought-tolerant) and Gannong No. 3 (drought-sensitive), were comparatively assayed when seedlings were exposed to -1.2 MPa polyethylene glycol (PEG-6000) treatments for 15 days. The results showed that the levels of proline, malondialdehyde (MDA), hydrogen peroxide (H2O2), hydroxyl free radical (OH•) and superoxide anion free radical (O2•-) in both varieties were significantly increased, while the root activity, the superoxide dismutase (SOD) and glutathione reductase (GR) activities, and the ratios of reduced/oxidized ascorbate (AsA/DHA) and reduced/oxidized glutathione (GSH/GSSG) were significantly decreased. The soluble protein and soluble sugar contents, the total antioxidant capability (T-AOC) and the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) first increased and then decreased with the increase in treatment days. Under osmotic stress, Longzhong exhibited lower levels of MDA, H2O2, OH• and O2•- but higher levels of SOD, CAT, APX, T-AOC and ratios of AsA/DHA and GSH/GSSG compared with Gannong No.3. Using isobaric tags for relative and absolute quantification (iTRAQ), 142 differentially accumulated proteins (DAPs) were identified from two alfalfa varieties, including 52 proteins (34 up-regulated and 18 down-regulated) in Longzhong, 71 proteins (28 up-regulated and 43 down-regulated) in Gannong No. 3, and 19 proteins (13 up-regulated and 6 down-regulated) shared by both varieties. Most of these DAPs were involved in stress and defense, protein metabolism, transmembrane transport, signal transduction, as well as cell wall and cytoskeleton metabolism. In conclusion, the stronger drought-tolerance of Longzhong was attributed to its higher osmotic adjustment capacity, greater ability to orchestrate its enzymatic and non-enzymatic antioxidant systems and thus avoid great oxidative damage in comparison to Gannong No. 3. Moreover, the involvement of other pathways, including carbohydrate metabolism, ROS detoxification, secondary metabolism, protein processing, ion and water transport, signal transduction, and cell wall adjustment, are important mechanisms for conferring drought tolerance in alfalfa.
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Affiliation(s)
- Cuimei Zhang
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Pratacultural Engineering Laboratory of Gansu Province, Sino-U.S. Centers for Grazing Land Ecosystem Sustainability, Gansu Agricultural University, Lanzhou, China
| | - Shangli Shi
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Pratacultural Engineering Laboratory of Gansu Province, Sino-U.S. Centers for Grazing Land Ecosystem Sustainability, Gansu Agricultural University, Lanzhou, China
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7
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Biogenic manganese oxide nanoparticle formation by a multimeric multicopper oxidase Mnx. Nat Commun 2017; 8:746. [PMID: 28963463 PMCID: PMC5622069 DOI: 10.1038/s41467-017-00896-8] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2017] [Accepted: 08/02/2017] [Indexed: 12/28/2022] Open
Abstract
Bacteria that produce Mn oxides are extraordinarily skilled engineers of nanomaterials that contribute significantly to global biogeochemical cycles. Their enzyme-based reaction mechanisms may be genetically tailored for environmental remediation applications or bioenergy production. However, significant challenges exist for structural characterization of the enzymes responsible for biomineralization. The active Mn oxidase in Bacillus sp. PL-12, Mnx, is a complex composed of a multicopper oxidase (MCO), MnxG, and two accessory proteins, MnxE and MnxF. MnxG shares sequence similarity with other, structurally characterized MCOs. MnxE and MnxF have no similarity to any characterized proteins. The ~200 kDa complex has been recalcitrant to crystallization, so its structure is unknown. Here, we show that native mass spectrometry defines the subunit topology and copper binding of Mnx, while high-resolution electron microscopy visualizes the protein and nascent Mn oxide minerals. These data provide critical structural information for understanding Mn biomineralization by such unexplored enzymes. Significant challenges exist for structural characterization of enzymes responsible for biomineralization. Here the authors show that native mass spectrometry and high resolution electron microscopy can define the subunit topology and copper binding of a manganese oxidizing complex, and describe early stage formation of its mineral products
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Simonov AN, Hocking RK, Tao L, Gengenbach T, Williams T, Fang XY, King HJ, Bonke SA, Hoogeveen DA, Romano CA, Tebo BM, Martin LL, Casey WH, Spiccia L. Tunable Biogenic Manganese Oxides. Chemistry 2017; 23:13482-13492. [PMID: 28722330 DOI: 10.1002/chem.201702579] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Indexed: 11/08/2022]
Abstract
Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx ) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.
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Affiliation(s)
- Alexandr N Simonov
- School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | - Rosalie K Hocking
- Discipline of Chemistry, College of Science and Engineering, James Cook University, Queensland, 4811, Australia
| | - Lizhi Tao
- Department of Chemistry, University of California, One Shields Avenue, Davis, California, 95616, USA
| | - Thomas Gengenbach
- Commonwealth Scientific and Industrial Research Organisation Manufacturing Flagship, Clayton, Victoria, 3168, Australia
| | - Timothy Williams
- Monash Centre for Electron Microscopy, Monash University, Victoria, 3800, Australia
| | - Xi-Ya Fang
- Monash Centre for Electron Microscopy, Monash University, Victoria, 3800, Australia
| | - Hannah J King
- Discipline of Chemistry, College of Science and Engineering, James Cook University, Queensland, 4811, Australia
| | - Shannon A Bonke
- School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | - Dijon A Hoogeveen
- School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | - Christine A Romano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA
| | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA
| | - Lisandra L Martin
- School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | - William H Casey
- Department of Chemistry, University of California, One Shields Avenue, Davis, California, 95616, USA.,Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, California, 95616, USA
| | - Leone Spiccia
- School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
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Soldatova AV, Romano CA, Tao L, Stich TA, Casey WH, Britt RD, Tebo BM, Spiro TG. Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Coordinated Two-Stage Mn(II)/(III) and Mn(III)/(IV) Mechanism. J Am Chem Soc 2017; 139:11381-11391. [PMID: 28712303 DOI: 10.1021/jacs.7b02772] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The bacterial manganese oxidase MnxG of the Mnx protein complex is unique among multicopper oxidases (MCOs) in carrying out a two-electron metal oxidation, converting Mn(II) to MnO2 nanoparticles. The reaction occurs in two stages: Mn(II) → Mn(III) and Mn(III) → MnO2. In a companion study , we show that the electron transfer from Mn(II) to the low-potential type 1 Cu of MnxG requires an activation step, likely forming a hydroxide bridge at a dinuclear Mn(II) site. Here we study the second oxidation step, using pyrophosphate (PP) as a Mn(III) trap. PP chelates Mn(III) produced by the enzyme and subsequently allows it to become a substrate for the second stage of the reaction. EPR spectroscopy confirms the presence of Mn(III) bound to the enzyme. The Mn(III) oxidation step does not involve direct electron transfer to the enzyme from Mn(III), which is shown by kinetic measurements to be excluded from the Mn(II) binding site. Instead, Mn(III) is proposed to disproportionate at an adjacent polynuclear site, thereby allowing indirect oxidation to Mn(IV) and recycling of Mn(II). PP plays a multifaceted role, slowing the reaction by complexing both Mn(II) and Mn(III) in solution, and also inhibiting catalysis, likely through binding at or near the active site. An overall mechanism for Mnx-catalyzed MnO2 production from Mn(II) is presented.
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Affiliation(s)
- Alexandra V Soldatova
- Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States
| | - Christine A Romano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University , Portland, Oregon 97239, United States
| | | | | | | | | | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University , Portland, Oregon 97239, United States
| | - Thomas G Spiro
- Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States
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10
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Soldatova AV, Tao L, Romano CA, Stich TA, Casey WH, Britt RD, Tebo BM, Spiro TG. Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism. J Am Chem Soc 2017; 139:11369-11380. [PMID: 28712284 DOI: 10.1021/jacs.7b02771] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO2 biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for the MnxG type 1 Cu2+, the electron acceptor. Indeed the type 1 Cu2+ is not reduced by Mn(II) in the absence of molecular oxygen, indicating that substrate oxidation requires an activation step. We have investigated the enzyme mechanism via electronic absorption spectroscopy, using chemometric analysis to separate enzyme-catalyzed MnO2 formation from MnO2 nanoparticle aging. The nanoparticle aging time course is characteristic of nucleation and particle growth; rates for these processes followed expected dependencies on Mn(II) concentration and temperature, but exhibited different pH optima. The enzymatic time course is sigmoidal, signaling an activation step, prior to turnover. The Mn(II) concentration and pH dependence of a preceding lag phase indicates weak Mn(II) binding. The activation step is enabled by a pKa > 8.6 deprotonation, which is assigned to Mn(II)-bound H2O; it induces a conformation change (consistent with a high activation energy, 106 kJ/mol) that increases Mn(II) affinity. Mnx activation is proposed to decrease the Mn(III/II) reduction potential below that of type 1 Cu(II/I) by formation of a hydroxide-bridged binuclear complex, Mn(II)(μ-OH)Mn(II), at the substrate site. Turnover is found to depend cooperatively on two Mn(II) and is enabled by a pKa 7.6 double deprotonation. It is proposed that turnover produces a Mn(III)(μ-OH)2Mn(III) intermediate that proceeds to the enzyme product, likely Mn(IV)(μ-O)2Mn(IV) or an oligomer, which subsequently nucleates MnO2 nanoparticles. We conclude that Mnx exploits manganese polynuclear chemistry in order to facilitate an otherwise difficult oxidation reaction, as well as biomineralization. The mechanism of the Mn(III/IV) conversion step is elucidated in an accompanying paper .
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Affiliation(s)
- Alexandra V Soldatova
- Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States
| | | | - Christine A Romano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University , Portland, Oregon 97239, United States
| | | | | | | | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University , Portland, Oregon 97239, United States
| | - Thomas G Spiro
- Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States
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11
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Tao L, Stich TA, Liou SH, Soldatova AV, Delgadillo DA, Romano CA, Spiro TG, Goodin DB, Tebo BM, Casey WH, Britt RD. Copper Binding Sites in the Manganese-Oxidizing Mnx Protein Complex Investigated by Electron Paramagnetic Resonance Spectroscopy. J Am Chem Soc 2017; 139:8868-8877. [DOI: 10.1021/jacs.7b02277] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
| | | | | | - Alexandra V. Soldatova
- Department
of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195, United States
| | - David A. Delgadillo
- Department of Chemistry & Chemical Biology, University of California, 5200 North Lake Road, Merced, California 95343, United States
| | - Christine A. Romano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Thomas G. Spiro
- Department
of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195, United States
| | | | - Bradley M. Tebo
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon 97239, United States
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12
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Butterfield CN, Tebo BM. Substrate specificity and copper loading of the manganese-oxidizing multicopper oxidase Mnx from Bacillus sp. PL-12. Metallomics 2017; 9:183-191. [DOI: 10.1039/c6mt00239k] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Tao L, Simonov AN, Romano CA, Butterfield CN, Fekete M, Tebo BM, Bond AM, Spiccia L, Martin LL, Casey WH. Biogenic Manganese-Oxide Mineralization is Enhanced by an Oxidative Priming Mechanism for the Multi-Copper Oxidase, MnxEFG. Chemistry 2016; 23:1346-1352. [PMID: 27726210 DOI: 10.1002/chem.201603803] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Indexed: 11/07/2022]
Abstract
In a natural geochemical cycle, manganese-oxide minerals (MnOx ) are principally formed through a microbial process, where a putative multicopper oxidase MnxG plays an essential role. Recent success in isolating the approximately 230 kDa, enzymatically active MnxEFG protein complex, has advanced our understanding of biogenic MnOx mineralization. Here, the kinetics of MnOx formation catalyzed by MnxEFG are examined using a quartz crystal microbalance (QCM), and the first electrochemical characterization of the MnxEFG complex is reported using Fourier transformed alternating current voltammetry. The voltammetric studies undertaken using near-neutral solutions (pH 7.8) establish the apparent reversible potentials for the Type 2 Cu sites in MnxEFG immobilized on a carboxy-terminated monolayer to be in the range 0.36-0.40 V versus a normal hydrogen electrode. Oxidative priming of the MnxEFG protein complex substantially enhances the enzymatic activity, as found by in situ electrochemical QCM analysis. The biogeochemical significance of this enzyme is clear, although the role of an oxidative priming of catalytic activity might be either an evolutionary advantage or an ancient relic of primordial existence.
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Affiliation(s)
- Lizhi Tao
- Department of Chemistry and Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, California, 95616, USA
| | - Alexandr N Simonov
- School of Chemistry, Monash University, Victoria, 3800, Australia.,ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | - Christine A Romano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA
| | - Cristina N Butterfield
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA.,Current address: Department of Earth and Planetary Science, University of California Berkeley, Berkeley, California, 94720, USA
| | - Monika Fekete
- School of Chemistry, Monash University, Victoria, 3800, Australia
| | - Bradley M Tebo
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA
| | - Alan M Bond
- School of Chemistry, Monash University, Victoria, 3800, Australia
| | - Leone Spiccia
- School of Chemistry, Monash University, Victoria, 3800, Australia.,ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia
| | | | - William H Casey
- Department of Chemistry and Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, California, 95616, USA
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The Role of Bacterial Spores in Metal Cycling and Their Potential Application in Metal Contaminant Bioremediation. Microbiol Spectr 2016; 4. [DOI: 10.1128/microbiolspec.tbs-0018-2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
ABSTRACT
Bacteria are one of the premier biological forces that, in combination with chemical and physical forces, drive metal availability in the environment. Bacterial spores, when found in the environment, are often considered to be dormant and metabolically inactive, in a resting state waiting for favorable conditions for them to germinate. However, this is a highly oversimplified view of spores in the environment. The surface of bacterial spores represents a potential site for chemical reactions to occur. Additionally, proteins in the outer layers (spore coats or exosporium) may also have more specific catalytic activity. As a consequence, bacterial spores can play a role in geochemical processes and may indeed find uses in various biotechnological applications. The aim of this review is to introduce the role of bacteria and bacterial spores in biogeochemical cycles and their potential use as toxic metal bioremediation agents.
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