1
|
Li B, Mao Z, Xue J, Xing P, Wu QL. Metabolic versatility of aerobic methane-oxidizing bacteria under anoxia in aquatic ecosystems. ENVIRONMENTAL MICROBIOLOGY REPORTS 2024; 16:e70002. [PMID: 39232853 PMCID: PMC11374530 DOI: 10.1111/1758-2229.70002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Accepted: 07/26/2024] [Indexed: 09/06/2024]
Abstract
The potential positive feedback between global aquatic deoxygenation and methane (CH4) emission emphasizes the importance of understanding CH4 cycling under O2-limited conditions. Increasing observations for aerobic CH4-oxidizing bacteria (MOB) under anoxia have updated the prevailing paradigm that MOB are O2-dependent; thus, clarification on the metabolic mechanisms of MOB under anoxia is critical and timely. Here, we mapped the global distribution of MOB under anoxic aquatic zones and summarized four underlying metabolic strategies for MOB under anoxia: (a) forming a consortium with oxygenic microorganisms; (b) self-generation/storage of O2 by MOB; (c) forming a consortium with non-oxygenic heterotrophic bacteria that use other electron acceptors; and (d) utilizing alternative electron acceptors other than O2. Finally, we proposed directions for future research. This study calls for improved understanding of MOB under anoxia, and underscores the importance of this overlooked CH4 sink amidst global aquatic deoxygenation.
Collapse
Affiliation(s)
- Biao Li
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
| | - Zhendu Mao
- Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
| | - Jingya Xue
- School of Geographical Sciences, Nanjing Normal University, Nanjing, China
| | - Peng Xing
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
| | - Qinglong L Wu
- Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
- Center for Evolution and Conservation Biology, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
- Sino-Danish Center for Education and Research, University of Chinese Academy of Sciences, Beijing, China
- The Fuxianhu Station of Plateau Deep Lake Research, Chinese Academy of Sciences, Yuxi, China
| |
Collapse
|
2
|
Peng W, Wang Z, Zhang Q, Yan S, Wang B. Unraveling the Valence State and Reactivity of Copper Centers in Membrane-Bound Particulate Methane Monooxygenase. J Am Chem Soc 2023; 145:25304-25317. [PMID: 37955571 DOI: 10.1021/jacs.3c08834] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
Particulate methane monooxygenase (pMMO) plays a critical role in catalyzing the conversion of methane to methanol, constituting the initial step in the C1 metabolic pathway within methanotrophic bacteria. However, the membrane-bound pMMO's structure and catalytic mechanism, notably the copper's valence state and genuine active site for methane oxidation, have remained elusive. Based on the recently characterized structure of membrane-bound pMMO, extensive computational studies were conducted to address these long-standing issues. A comprehensive analysis comparing the quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulated structures with cryo-EM data indicates that both the CuC and CuD sites tend to stay in the Cu(I) valence state within the membrane environment. Additionally, the concurrent presence of Cu(I) at both CuC and CuD sites leads to the significant reduction of the ligand-binding cavity situated between them, making it less likely to accommodate a reductant molecule such as durohydroquinone (DQH2). Subsequent QM/MM calculations reveal that the CuD(I) site is more reactive than the CuC(I) site in oxygen activation, en route to H2O2 formation and the generation of Cu(II)-O•- species. Finally, our simulations demonstrate that the natural reductant ubiquinol (CoQH2) assumes a productive binding conformation at the CuD(I) site but not at the CuC(I) site. This provides evidence that the true active site of membrane-bound pMMOs may be CuD rather than CuC. These findings clarify pMMO's catalytic mechanism and emphasize the membrane environment's pivotal role in modulating the coordination structure and the activity of copper centers within pMMO.
Collapse
Affiliation(s)
- Wei Peng
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering and Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen University, Xiamen 361005, P. R. China
- Key Laboratory of Aerosol Chemistry and Physics, State Key Laboratory of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, P. R. China
| | - Zikuan Wang
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr 45470, Germany
| | - Qiaoyu Zhang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering and Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen University, Xiamen 361005, P. R. China
| | - Shengheng Yan
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering and Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen University, Xiamen 361005, P. R. China
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering and Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen University, Xiamen 361005, P. R. China
| |
Collapse
|
3
|
Hwang Y, Na JG, Lee SJ. Transcriptional regulation of soluble methane monooxygenase via enhancer-binding protein derived from Methylosinus sporium 5. Appl Environ Microbiol 2023; 89:e0210422. [PMID: 37668365 PMCID: PMC10537576 DOI: 10.1128/aem.02104-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 07/07/2023] [Indexed: 09/06/2023] Open
Abstract
Methane is a major greenhouse gas, and methanotrophs regulate the methane level in the carbon cycle. Soluble methane monooxygenase (sMMO) is expressed in various methanotroph genera, including Alphaproteobacteria and Gammaproteobacteria, and catalyzes the hydroxylation of methane to methanol. It has been proposed that MmoR regulates the expression of sMMO as an enhancer-binding protein under copper-limited conditions; however, details on this transcriptional regulation remain limited. Herein, we elucidate the transcriptional pathway of sMMO depending on copper ion concentration, which affects the interaction of MmoR and sigma factor. MmoR and sigma-54 (σ54) from Methylosinus sporium 5 were successfully overexpressed in Escherichia coli and purified to investigate sMMO transcription in methanotrophs. The results indicated that σ54 binds to a promoter positioned -24 (GG) and -12 (TGC) upstream between mmoG and mmoX1. The binding affinity and selectivity are lower (Kd = 184.6 ± 6.2 nM) than those of MmoR. MmoR interacts with the upstream activator sequence (UAS) with a strong binding affinity (Kd = 12.5 ± 0.5 nM). Mutational studies demonstrated that MmoR has high selectivity to its binding partner (ACA-xx-TGT). Titration assays have demonstrated that MmoR does not coordinate with copper ions directly; however, its binding affinity to UAS decreases in a low-copper-containing medium. MmoR strongly interacts with adenosine triphosphate (Kd = 62.8 ± 0.5 nM) to generate RNA polymerase complex. This study demonstrated that the binding events of both MmoR and σ54 that regulate transcription in M. sporium 5 depend on the copper ion concentration. IMPORTANCE This study provides biochemical evidence of transcriptional regulation of soluble methane monooxygenase (sMMO) in methanotrophs that control methane levels in ecological systems. Previous studies have proposed transcriptional regulation of MMOs, including sMMO and pMMO, while we provide further evidence to elucidate its mechanism using a purified enhancer-binding protein (MmoR) and transcription factor (σ54). The characterization studies of σ54 and MmoR identified the promoter binding sites and enhancer-binding sequences essential for sMMO expression. Our findings also demonstrate that MmoR functions as a trigger for sMMO expression due to the high specificity and selectivity for enhancer-binding sequences. The UV-visible spectrum of purified MmoR suggested an iron coordination like other GAF domain, and that ATP is essential for the initiation of enhancer elements. Binding assays indicated that these interactions are blocked by the copper ion. These results provide novel insights into gene regulation of methanotrophs.
Collapse
Affiliation(s)
- Yunha Hwang
- Department of Chemistry, Jeonbuk National University , Jeonju, South Korea
| | - Jeong-Geol Na
- Department of Chemical Engineering, Sogang University , Seoul, South Korea
| | - Seung Jae Lee
- Department of Chemistry, Jeonbuk National University , Jeonju, South Korea
- Institute of Molecular Biology and Genetics, Jeonbuk National University , Jeonju, South Korea
| |
Collapse
|
4
|
Evidence for methanobactin "Theft" and novel chalkophore production in methanotrophs: impact on methanotrophic-mediated methylmercury degradation. THE ISME JOURNAL 2022; 16:211-220. [PMID: 34290379 PMCID: PMC8692452 DOI: 10.1038/s41396-021-01062-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Revised: 07/02/2021] [Accepted: 07/08/2021] [Indexed: 02/07/2023]
Abstract
Aerobic methanotrophy is strongly controlled by copper, and methanotrophs are known to use different mechanisms for copper uptake. Some methanotrophs secrete a modified polypeptide-methanobactin-while others utilize a surface-bound protein (MopE) and a secreted form of it (MopE*) for copper collection. As different methanotrophs have different means of sequestering copper, competition for copper significantly impacts methanotrophic activity. Herein, we show that Methylomicrobium album BG8, Methylocystis sp. strain Rockwell, and Methylococcus capsulatus Bath, all lacking genes for methanobactin biosynthesis, are not limited for copper by multiple forms of methanobactin. Interestingly, Mm. album BG8 and Methylocystis sp. strain Rockwell were found to have genes similar to mbnT that encodes for a TonB-dependent transporter required for methanobactin uptake. Data indicate that these methanotrophs "steal" methanobactin and such "theft" enhances the ability of these strains to degrade methylmercury, a potent neurotoxin. Further, when mbnT was deleted in Mm. album BG8, methylmercury degradation in the presence of methanobactin was indistinguishable from when MB was not added. Mc. capsulatus Bath lacks anything similar to mbnT and was unable to degrade methylmercury either in the presence or absence of methanobactin. Rather, Mc. capsulatus Bath appears to rely on MopE/MopE* for copper collection. Finally, not only does Mm. album BG8 steal methanobactin, it synthesizes a novel chalkophore, suggesting that some methanotrophs utilize both competition and cheating strategies for copper collection. Through a better understanding of these strategies, methanotrophic communities may be more effectively manipulated to reduce methane emissions and also enhance mercury detoxification in situ.
Collapse
|
5
|
Karthikeyan OP, Smith TJ, Dandare SU, Parwin KS, Singh H, Loh HX, Cunningham MR, Williams PN, Nichol T, Subramanian A, Ramasamy K, Kumaresan D. Metal(loid) speciation and transformation by aerobic methanotrophs. MICROBIOME 2021; 9:156. [PMID: 34229757 PMCID: PMC8262016 DOI: 10.1186/s40168-021-01112-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 06/09/2021] [Indexed: 05/06/2023]
Abstract
Manufacturing and resource industries are the key drivers for economic growth with a huge environmental cost (e.g. discharge of industrial effluents and post-mining substrates). Pollutants from waste streams, either organic or inorganic (e.g. heavy metals), are prone to interact with their physical environment that not only affects the ecosystem health but also the livelihood of local communities. Unlike organic pollutants, heavy metals or trace metals (e.g. chromium, mercury) are non-biodegradable, bioaccumulate through food-web interactions and are likely to have a long-term impact on ecosystem health. Microorganisms provide varied ecosystem services including climate regulation, purification of groundwater, rehabilitation of contaminated sites by detoxifying pollutants. Recent studies have highlighted the potential of methanotrophs, a group of bacteria that can use methane as a sole carbon and energy source, to transform toxic metal (loids) such as chromium, mercury and selenium. In this review, we synthesise recent advances in the role of essential metals (e.g. copper) for methanotroph activity, uptake mechanisms alongside their potential to transform toxic heavy metal (loids). Case studies are presented on chromium, selenium and mercury pollution from the tanneries, coal burning and artisanal gold mining, respectively, which are particular problems in the developing economy that we propose may be suitable for remediation by methanotrophs. Video Abstract.
Collapse
Affiliation(s)
- Obulisamy Parthiba Karthikeyan
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
- Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI USA
- Department of Engineering Technology, College of Technology, University of Houston, Houston, TX USA
| | - Thomas J. Smith
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Sheffield, UK
| | - Shamsudeen Umar Dandare
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
| | - Kamaludeen Sara Parwin
- Department of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore, India
| | - Heetasmin Singh
- Department of Chemistry, University of Guyana, Georgetown, Guyana
| | - Hui Xin Loh
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
| | - Mark R Cunningham
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
| | - Paul Nicholas Williams
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
| | - Tim Nichol
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Sheffield, UK
| | | | | | - Deepak Kumaresan
- School of Biological Sciences & Institute for Global Food Security, Queen’s University Belfast, 19 Chlorine Gardens, Belfast, UK
| |
Collapse
|
6
|
Abstract
Methanobactins (MBs) are small (<1,300-Da) posttranslationally modified copper-binding peptides and represent the extracellular component of a copper acquisition system in some methanotrophs. Interestingly, MBs can bind a range of metal ions, with some being reduced after binding, e.g., Cu2+ reduced to Cu+. Other metal ions, however, are bound but not reduced, e.g., K+. The source of electrons for selective metal ion reduction has been speculated to be water but never empirically shown. Here, using H218O, we show that when MBs from Methylocystis sp. strain SB2 (MB-SB2) and Methylosinus trichosporium OB3b (MB-OB3) were incubated in the presence of either Au3+, Cu2, or Ag+, 18,18O2 and free protons were released. No 18,18O2 production was observed in the presence of either MB-SB2 or MB-OB3b alone, gold alone, copper alone, or silver alone or when K+ or Mo2+ was incubated with MB-SB2. In contrast to MB-OB3b, MB-SB2 binds Fe3+ with an N2S2 coordination and will also reduce Fe3+ to Fe2+. Iron reduction was also found to be coupled to the oxidation of 2H2O and the generation of O2. MB-SB2 will also couple Hg2+, Ni2+, and Co2+ reduction to the oxidation of 2H2O and the generation of O2, but MB-OB3b will not, ostensibly as MB-OB3b binds but does not reduce these metal ions. To determine if the O2 generated during metal ion reduction by MB could be coupled to methane oxidation, 13CH4 oxidation by Methylosinus trichosporium OB3b was monitored under anoxic conditions. The results demonstrate that O2 generation from metal ion reduction by MB-OB3b can support methane oxidation. IMPORTANCE The discovery that MB will couple the oxidation of H2O to metal ion reduction and the release of O2 suggests that methanotrophs expressing MB may be able to maintain their activity under hypoxic/anoxic conditions through the “self-generation” of dioxygen required for the initial oxidation of methane to methanol. Such an ability may be an important factor in enabling methanotrophs to not only colonize the oxic-anoxic interface where methane concentrations are highest but also tolerate significant temporal fluctuations of this interface. Given that genomic surveys often show evidence of aerobic methanotrophs within anoxic zones, the ability to express MB (and thereby generate dioxygen) may be an important parameter in facilitating their ability to remove methane, a potent greenhouse gas, before it enters the atmosphere.
Collapse
|
7
|
Avdeeva LV, Gvozdev RI. Oxidation of L-Ascorbic Acid in the Presence of the Copper-Binding Compound from Methanotrophic Bacteria Methylococcus capsulatus (M). Biomimetics (Basel) 2020; 5:biomimetics5040048. [PMID: 33049942 PMCID: PMC7709488 DOI: 10.3390/biomimetics5040048] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 10/03/2020] [Accepted: 10/06/2020] [Indexed: 11/16/2022] Open
Abstract
The oxidation of ascorbic acid by air oxygen and hydrogen peroxide in the presence of the copper-binding compound (cbc) from bacteria Methylococcus capsulatus (M) was studied. The rate constant of ascorbic acid oxidation by air oxygen in the presence of the copper complex with cbc from M. capsulatus (M) was shown to be 1.5 times higher than that of the noncatalytic reaction. The rate constant of ascorbic acid oxidation by hydrogen peroxide in the presence of the copper complex with cbc from M. capsulatus (M) decreased by almost one-third compared to the reaction in the absence of the copper complex with cbc. It was assumed that cbc can be involved in a multilevel system of antioxidant protection and can protect a bacterial cell from oxidation stress. Thus, the cbc is mimetic ascorbate oxidase in the oxidation of ascorbic acid by molecular oxygen.
Collapse
|
8
|
Semrau JD, DiSpirito AA, Obulisamy PK, Kang-Yun CS. Methanobactin from methanotrophs: genetics, structure, function and potential applications. FEMS Microbiol Lett 2020; 367:5804726. [PMID: 32166327 DOI: 10.1093/femsle/fnaa045] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 03/11/2020] [Indexed: 12/12/2022] Open
Abstract
Aerobic methane-oxidizing bacteria of the Alphaproteobacteria have been found to express a novel ribosomally synthesized post-translationally modified polypeptide (RiPP) termed methanobactin (MB). The primary function of MB in these microbes appears to be for copper uptake, but MB has been shown to have multiple capabilities, including oxidase, superoxide dismutase and hydrogen peroxide reductase activities, the ability to detoxify mercury species, as well as acting as an antimicrobial agent. Herein, we describe the diversity of known MBs as well as the genetics underlying MB biosynthesis. We further propose based on bioinformatics analyses that some methanotrophs may produce novel forms of MB that have yet to be characterized. We also discuss recent findings documenting that MBs play an important role in controlling copper availability to the broader microbial community, and as a result can strongly affect the activity of microbes that require copper for important enzymatic transformations, e.g. conversion of nitrous oxide to dinitrogen. Finally, we describe procedures for the detection/purification of MB, as well as potential medical and industrial applications of this intriguing RiPP.
Collapse
Affiliation(s)
- Jeremy D Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA 48109-2125
| | - Alan A DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, USA 50011
| | | | - Christina S Kang-Yun
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA 48109-2125
| |
Collapse
|
9
|
Hofmann M, Retamal-Morales G, Tischler D. Metal binding ability of microbial natural metal chelators and potential applications. Nat Prod Rep 2020; 37:1262-1283. [DOI: 10.1039/c9np00058e] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Metallophores can chelate many different metal and metalloid ions next to iron, make them valuable for many applications.
Collapse
Affiliation(s)
- Marika Hofmann
- Institute of Biosciences
- Chemistry and Physics Faculty
- TU Bergakademie Freiberg
- 09599 Freiberg
- Germany
| | - Gerardo Retamal-Morales
- Laboratorio de Microbiología Básica y Aplicada
- Facultad de Química y Biología
- Universidad de Santiago de Chile
- Santiago
- Chile
| | - Dirk Tischler
- Microbial Biotechnology
- Ruhr-Universität Bochum
- 44780 Bochum
- Germany
| |
Collapse
|
10
|
Avdeeva LV, Gvozdev RI. Effect of Heavy Metal Salts on Propylene Oxidation by Methanotrophic Bacteria. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY B 2019. [DOI: 10.1134/s1990793119060022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
11
|
Semrau JD, DiSpirito AA. Methanobactin: A Novel Copper-Binding Compound Produced by Methanotrophs. ACTA ACUST UNITED AC 2019. [DOI: 10.1007/978-3-030-23261-0_7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
|
12
|
Abstract
Copper-binding metallophores, or chalkophores, play a role in microbial copper homeostasis that is analogous to that of siderophores in iron homeostasis. The best-studied chalkophores are members of the methanobactin (Mbn) family-ribosomally produced, posttranslationally modified natural products first identified as copper chelators responsible for copper uptake in methane-oxidizing bacteria. To date, Mbns have been characterized exclusively in those species, but there is genomic evidence for their production in a much wider range of bacteria. This review addresses the current state of knowledge regarding the function, biosynthesis, transport, and regulation of Mbns. While the roles of several proteins in these processes are supported by substantial genetic and biochemical evidence, key aspects of Mbn manufacture, handling, and regulation remain unclear. In addition, other natural products that have been proposed to mediate copper uptake as well as metallophores that have biologically relevant roles involving copper binding, but not copper uptake, are discussed.
Collapse
Affiliation(s)
- Grace E Kenney
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA; ,
| | - Amy C Rosenzweig
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA; ,
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| |
Collapse
|
13
|
Li Y, Wang Y, Lin Z, Wang J, He Q, Zhou J. A novel methanotrophic co-metabolic system with high soluble methane monooxygenase activity to biodegrade refractory organics in pulping wastewater. BIORESOURCE TECHNOLOGY 2018; 256:358-365. [PMID: 29471231 DOI: 10.1016/j.biortech.2018.02.048] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/09/2018] [Accepted: 02/10/2018] [Indexed: 06/08/2023]
Abstract
Pulping wastewater still contains massive refractory organics after biotreatment, with high colority, low biodegradability, and lasting biotoxicity. To eliminate refractory organics in pulping wastewater, a methanotrophic co-metabolic system in a gas cycle Sequencing Batch Biofilm Reactor (gcSBBR) seeded by soil at a ventilation opening of coal mine was quickly built on the 92nd day. The removal rate of COD, colority and TOC was 53.28%, 50.59% and 51.60%, respectively. Analysis of 3D-EEM indicated that glycolated protein-like, melanoidin-like or lignocellulose-like, and humic acid-like decreased by 7.85%, 5.02% and 1.74%, respectively. Moreover, this system exhibited high activity of soluble methane monooxygenase (sMMO) and mmoX encoding sMMO reached up to 7.89 × 105 copies/μL. Methanotrophs, namely, Methylocaldum (8.28%), Methylococcus (6.06%) and Methylomonas (0.07%), were detected by 16S rRNA sequencing. And other bacteria were dominated by Denitratisoma, Anaerolineaceae_uncultured and Methylophilaceae_uncultured. Refractory organics was biodegraded through the synergy among microorganisms, and a postulated synergy pathway was put forward.
Collapse
Affiliation(s)
- Yancheng Li
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China
| | - Yingmu Wang
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China
| | - Ziyuan Lin
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China
| | - Jiale Wang
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China
| | - Qiang He
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China
| | - Jian Zhou
- Key Laboratory of the Three Gorges Reservoir's Eco-Environments, Chongqing University, Chongqing 400045, PR China.
| |
Collapse
|
14
|
Kenney GE, Rosenzweig AC. Methanobactins: Maintaining copper homeostasis in methanotrophs and beyond. J Biol Chem 2018; 293:4606-4615. [PMID: 29348173 PMCID: PMC5880147 DOI: 10.1074/jbc.tm117.000185] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Methanobactins (Mbns) are ribosomally produced, post-translationally modified natural products that bind copper with high affinity and specificity. Originally identified in methanotrophic bacteria, which have a high need for copper, operons encoding these compounds have also been found in many non-methanotrophic bacteria. The proteins responsible for Mbn biosynthesis include several novel enzymes. Mbn transport involves export through a multidrug efflux pump and re-internalization via a TonB-dependent transporter. Release of copper from Mbn and the molecular basis for copper regulation of Mbn production remain to be elucidated. Future work is likely to result in the identification of new enzymatic chemistry, opportunities for bioengineering and drug targeting of copper metabolism, and an expanded understanding of microbial metal homeostasis.
Collapse
Affiliation(s)
- Grace E Kenney
- Departments of Molecular Biosciences, Evanston, Illinois 60208
| | - Amy C Rosenzweig
- Departments of Molecular Biosciences, Evanston, Illinois 60208; Chemistry, Northwestern University, Evanston, Illinois 60208.
| |
Collapse
|
15
|
McCabe JW, Vangala R, Angel LA. Binding Selectivity of Methanobactin from Methylosinus trichosporium OB3b for Copper(I), Silver(I), Zinc(II), Nickel(II), Cobalt(II), Manganese(II), Lead(II), and Iron(II). JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:2588-2601. [PMID: 28856622 DOI: 10.1007/s13361-017-1778-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 08/03/2017] [Accepted: 08/04/2017] [Indexed: 05/22/2023]
Abstract
Methanobactin (Mb) from Methylosinus trichosporium OB3b is a member of a class of metal binding peptides identified in methanotrophic bacteria. Mb will selectively bind and reduce Cu(II) to Cu(I), and is thought to mediate the acquisition of the copper cofactor for the enzyme methane monooxygenase. These copper chelating properties of Mb make it potentially useful as a chelating agent for treatment of diseases where copper plays a role including Wilson's disease, cancers, and neurodegenerative diseases. Utilizing traveling wave ion mobility-mass spectrometry (TWIMS), the competition for the Mb copper binding site from Ag(I), Pb(II), Co(II), Fe(II), Mn(II), Ni(II), and Zn(II) has been determined by a series of metal ion titrations, pH titrations, and metal ion displacement titrations. The TWIMS analyses allowed for the explicit identification and quantification of all the individual Mb species present during the titrations and measured their collision cross-sections and collision-induced dissociation patterns. The results showed Ag(I) and Ni(II) could irreversibly bind to Mb and not be effectively displaced by Cu(I), whereas Ag(I) could also partially displace Cu(I) from the Mb complex. At pH ≈ 6.5, the Mb binding selectivity follows the order Ag(I)≈Cu(I)>Ni(II)≈Zn(II)>Co(II)>>Mn(II)≈Pb(II)>Fe(II), and at pH 7.5 to 10.4 the order is Ag(I)>Cu(I)>Ni(II)>Co(II)>Zn(II)>Mn(II)≈Pb(II)>Fe(II). Breakdown curves of the disulfide reduced Cu(I) and Ag(I) complexes showed a correlation existed between their relative stability and their compact folded structure indicated by their CCS. Fluorescence spectroscopy, which allowed the determination of the binding constant, compared well with the TWIMS analyses, with the exception of the Ni(II) complex. Graphical abstract ᅟ.
Collapse
Affiliation(s)
- Jacob W McCabe
- Department of Chemistry, Texas A&M University-Commerce, Commerce, TX, 75428, USA
| | - Rajpal Vangala
- Department of Chemistry, Texas A&M University-Commerce, Commerce, TX, 75428, USA
| | - Laurence A Angel
- Department of Chemistry, Texas A&M University-Commerce, Commerce, TX, 75428, USA.
| |
Collapse
|
16
|
Abstract
Methanobactins (Mbns) are ribosomally produced, post-translationally modified peptide (RiPP) natural products that bind copper with high affinity using nitrogen-containing heterocycles and thioamide groups. In some methanotrophic bacteria, Mbns are secreted under conditions of copper starvation and then re-internalized as a copper source for the enzyme particulate methane monooxygenase (pMMO). Genome mining studies have led to the identification and classification of operons encoding the Mbn precursor peptide (MbnA) as well as a number of putative transport, regulatory, and biosynthetic proteins. These Mbn operons are present in non-methanotrophic bacteria as well, suggesting a broader role in and perhaps beyond copper acquisition. Genetic and biochemical studies indicate that specific operon-encoded proteins are involved in Mbn transport and provide insight into copper-responsive gene regulation in methanotrophs. Mbn biosynthesis is not yet understood, but combined analysis of Mbn structures, MbnA sequences, and operon content represents a powerful approach to elucidating the roles of specific biosynthetic enzymes. Future work will likely lead to the discovery of unique pathways for natural product biosynthesis and new mechanisms of microbial metal homeostasis.
Collapse
Affiliation(s)
- Laura M K Dassama
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
| | - Grace E Kenney
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
| | - Amy C Rosenzweig
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA. and Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| |
Collapse
|
17
|
Lu X, Gu W, Zhao L, Farhan Ul Haque M, DiSpirito AA, Semrau JD, Gu B. Methylmercury uptake and degradation by methanotrophs. SCIENCE ADVANCES 2017; 3:e1700041. [PMID: 28580426 PMCID: PMC5451197 DOI: 10.1126/sciadv.1700041] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/30/2017] [Indexed: 05/22/2023]
Abstract
Methylmercury (CH3Hg+) is a potent neurotoxin produced by certain anaerobic microorganisms in natural environments. Although numerous studies have characterized the basis of mercury (Hg) methylation, no studies have examined CH3Hg+ degradation by methanotrophs, despite their ubiquitous presence in the environment. We report that some methanotrophs, such as Methylosinus trichosporium OB3b, can take up and degrade CH3Hg+ rapidly, whereas others, such as Methylococcus capsulatus Bath, can take up but not degrade CH3Hg+. Demethylation by M. trichosporium OB3b increases with increasing CH3Hg+ concentrations but was abolished in mutants deficient in the synthesis of methanobactin, a metal-binding compound used by some methanotrophs, such as M. trichosporium OB3b. Furthermore, addition of methanol (>5 mM) as a competing one-carbon (C1) substrate inhibits demethylation, suggesting that CH3Hg+ degradation by methanotrophs may involve an initial bonding of CH3Hg+ by methanobactin followed by cleavage of the C-Hg bond in CH3Hg+ by the methanol dehydrogenase. This new demethylation pathway by methanotrophs indicates possible broader involvement of C1-metabolizing aerobes in the degradation and cycling of toxic CH3Hg+ in the environment.
Collapse
Affiliation(s)
- Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Wenyu Gu
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Muhammad Farhan Ul Haque
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Alan A. DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jeremy D. Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Corresponding author.
| |
Collapse
|
18
|
Avdeeva L, Gvozdev R. Effect of Copper Concentration on the Growth of Methylococcus Capsulatus (Strain М). CHEMISTRY JOURNAL OF MOLDOVA 2017. [DOI: 10.19261/cjm.2017.404] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
|
19
|
DiSpirito AA, Semrau JD, Murrell JC, Gallagher WH, Dennison C, Vuilleumier S. Methanobactin and the Link between Copper and Bacterial Methane Oxidation. Microbiol Mol Biol Rev 2016; 80:387-409. [PMID: 26984926 PMCID: PMC4867365 DOI: 10.1128/mmbr.00058-15] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Methanobactins (mbs) are low-molecular-mass (<1,200 Da) copper-binding peptides, or chalkophores, produced by many methane-oxidizing bacteria (methanotrophs). These molecules exhibit similarities to certain iron-binding siderophores but are expressed and secreted in response to copper limitation. Structurally, mbs are characterized by a pair of heterocyclic rings with associated thioamide groups that form the copper coordination site. One of the rings is always an oxazolone and the second ring an oxazolone, an imidazolone, or a pyrazinedione moiety. The mb molecule originates from a peptide precursor that undergoes a series of posttranslational modifications, including (i) ring formation, (ii) cleavage of a leader peptide sequence, and (iii) in some cases, addition of a sulfate group. Functionally, mbs represent the extracellular component of a copper acquisition system. Consistent with this role in copper acquisition, mbs have a high affinity for copper ions. Following binding, mbs rapidly reduce Cu(2+) to Cu(1+). In addition to binding copper, mbs will bind most transition metals and near-transition metals and protect the host methanotroph as well as other bacteria from toxic metals. Several other physiological functions have been assigned to mbs, based primarily on their redox and metal-binding properties. In this review, we examine the current state of knowledge of this novel type of metal-binding peptide. We also explore its potential applications, how mbs may alter the bioavailability of multiple metals, and the many roles mbs may play in the physiology of methanotrophs.
Collapse
Affiliation(s)
- Alan A DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, USA
| | - Jeremy D Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA
| | - J Colin Murrell
- Earth and Life Systems Alliance, School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
| | - Warren H Gallagher
- Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin, USA
| | - Christopher Dennison
- Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Stéphane Vuilleumier
- Department of Microbiology, Genomics and the Environment, UMR 7156 UNISTRA-CNRS, Université de Strasbourg, Strasbourg, France
| |
Collapse
|
20
|
Larsen Ø, Karlsen OA. Transcriptomic profiling of Methylococcus capsulatus (Bath) during growth with two different methane monooxygenases. Microbiologyopen 2016; 5:254-67. [PMID: 26687591 PMCID: PMC4831470 DOI: 10.1002/mbo3.324] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Revised: 11/04/2015] [Accepted: 11/06/2015] [Indexed: 11/23/2022] Open
Abstract
Methylococcus capsulatus (Bath) is a methanotroph that possesses both a membrane-embedded (pMMO) and a soluble methane monooxygenase (sMMO). The expression of these two MMO's is tightly controlled by the availability of copper in the growth medium, but the underlying mechanisms and the number of genes involved in this switch in methane oxidation is not yet fully elucidated. Microarray analyses were used to assess the transcriptome in cells producing either pMMO or sMMO. A total of 137 genes were differentially expressed, with 87 genes showing a significant up-regulation during sMMO production. The majority of the differentially expressed genes could be assigned to functional roles in the energy metabolism and transport. Furthermore, three copper responding gene clusters were discovered, including an extended cluster that also harbors the genes for sMMO. Our data also indicates that major changes takes place in the respiratory chain between pMMO- and sMMO-producing cells, and that quinone are predominantly used as the electron donors for methane oxidation by pMMO. Intriguingly, a large proportion of the differentially expressed genes between pMMO- and sMMO-producing cells encode c-type cytochromes. By combining microarray- and mass spectrometry data, a total of 35 c-type cytochromes are apparently expressed in M. capsulatus when grown in nitrate mineral salt medium with methane as sole energy and carbon source, and the expression of 21 of these respond to the availability of copper. Interestingly, several of these c-type cytochromes are recovered from the cell surface, suggesting that extracellular electron transfers may occur in M. capsulatus.
Collapse
Affiliation(s)
- Øivind Larsen
- Uni Research EnvironmentThormøhlensgate 49bBergen5006Norway
| | - Odd A. Karlsen
- Department of Molecular BiologyUniversity of BergenBergenNorway
| |
Collapse
|
21
|
|
22
|
Choi D, Alshahrani AA, Vytla Y, Deeconda M, Serna VJ, Saenz RF, Angel LA. Redox activity and multiple copper(I) coordination of 2His-2Cys oligopeptide. JOURNAL OF MASS SPECTROMETRY : JMS 2015; 50:316-25. [PMID: 25800013 DOI: 10.1002/jms.3530] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 10/13/2014] [Accepted: 10/14/2014] [Indexed: 05/07/2023]
Abstract
Copper binding motifs with their molecular mechanisms of selective copper(I) recognition are essential molecules for acquiring copper ions, trafficking copper to specific locations and controlling the potentially damaging redox activities of copper in biochemical processes. The redox activity and multiple Cu(I) binding of an analog methanobactin peptide-2 (amb2) with the sequence acetyl-His1-Cys2-Tyr3-Pro4-His5-Cys6 was investigated using ion mobility-mass spectrometry (IM-MS) and UV-Vis spectrophotometry analyses. The Cu(II) titration of amb2 showed oxidation of amb2 via the formation of intra- and intermolecular Cys-Cys disulfide bridges and the multiple Cu(I) coordination by unoxidized amb2 or the partially oxidized dimer and trimer of amb2. The principal product of these reactions was [amb2 + 3Cu(I)](+) which probably coordinates the three Cu(I) ions via two bridging thiolate groups of Cys2 and Cys6 and the δN6 of the imidazole groups of His6, as determined by geometry optimized structures at the B3LYP/LanL2DZ level of theory. The products observed by IM-MS showed direct correlation to spectral changes associated with disulfide bond formation in the UV-Vis spectrophotometric study. The results show that IM-MS analysis is a powerful technique for unambiguously determining the major ion species produced during the redox and metal binding chemistry of oligopeptides.
Collapse
Affiliation(s)
- DongWon Choi
- Department of Biology and Environmental Sciences, Texas A&M University-Commerce, TX, 75428, USA
| | | | | | | | | | | | | |
Collapse
|
23
|
Solomon EI, Heppner DE, Johnston EM, Ginsbach JW, Cirera J, Qayyum M, Kieber-Emmons MT, Kjaergaard CH, Hadt RG, Tian L. Copper active sites in biology. Chem Rev 2014; 114:3659-853. [PMID: 24588098 PMCID: PMC4040215 DOI: 10.1021/cr400327t] [Citation(s) in RCA: 1138] [Impact Index Per Article: 113.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
| | - David E. Heppner
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | | | - Jake W. Ginsbach
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Jordi Cirera
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Munzarin Qayyum
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | | | | | - Ryan G. Hadt
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Li Tian
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| |
Collapse
|
24
|
Johnson KA, Ve T, Larsen Ø, Pedersen RB, Lillehaug JR, Jensen HB, Helland R, Karlsen OA. CorA is a copper repressible surface-associated copper(I)-binding protein produced in Methylomicrobium album BG8. PLoS One 2014; 9:e87750. [PMID: 24498370 PMCID: PMC3912023 DOI: 10.1371/journal.pone.0087750] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Accepted: 12/30/2013] [Indexed: 11/18/2022] Open
Abstract
CorA is a copper repressible protein previously identified in the methanotrophic bacterium Methylomicrobium album BG8. In this work, we demonstrate that CorA is located on the cell surface and binds one copper ion per protein molecule, which, based on X-ray Absorption Near Edge Structure analysis, is in the reduced state (Cu(I)). The structure of endogenously expressed CorA was solved using X-ray crystallography. The 1.6 Å three-dimensional structure confirmed the binding of copper and revealed that the copper atom was coordinated in a mononuclear binding site defined by two histidines, one water molecule, and the tryptophan metabolite, kynurenine. This arrangement of the copper-binding site is similar to that of its homologous protein MopE* from Metylococcus capsulatus Bath, confirming the importance of kynurenine for copper binding in these proteins. Our findings show that CorA has an overall fold similar to MopE, including the unique copper(I)-binding site and most of the secondary structure elements. We suggest that CorA plays a role in the M. album BG8 copper acquisition.
Collapse
Affiliation(s)
- Kenneth A. Johnson
- Norwegian Structural Biology Centre, Faculty of Science, University of Tromsø, Tromsø, Norway
| | - Thomas Ve
- Department of Molecular Biology, University of Bergen, Bergen, Norway
| | - Øivind Larsen
- Department of Molecular Biology, University of Bergen, Bergen, Norway
| | - Rolf B. Pedersen
- Department of Earth Science - Centre for Geobiology, University of Bergen, Bergen, Norway
| | | | - Harald B. Jensen
- Department of Molecular Biology, University of Bergen, Bergen, Norway
| | - Ronny Helland
- Norwegian Structural Biology Centre, Faculty of Science, University of Tromsø, Tromsø, Norway
| | - Odd A. Karlsen
- Department of Molecular Biology, University of Bergen, Bergen, Norway
- * E-mail:
| |
Collapse
|
25
|
Khmelenina VN, Suzina NE, Trotsenko YA. Surface layers of methanotrophic bacteria. Microbiology (Reading) 2013. [DOI: 10.1134/s0026261713050068] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
|
26
|
Detoxification of mercury by methanobactin from Methylosinus trichosporium OB3b. Appl Environ Microbiol 2013; 79:5918-26. [PMID: 23872554 DOI: 10.1128/aem.01673-13] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many methanotrophs have been shown to synthesize methanobactin, a novel biogenic copper-chelating agent or chalkophore. Methanobactin binds copper via two heterocyclic rings with associated enethiol groups. The structure of methanobactin suggests that it can bind other metals, including mercury. Here we report that methanobactin from Methylosinus trichosporium OB3b does indeed bind mercury when added as HgCl2 and, in doing so, reduced toxicity associated with Hg(II) for both Alphaproteobacteria methanotrophs, including M. trichosporium OB3b, M. trichosporium OB3b ΔmbnA (a mutant defective in methanobactin production), and Methylocystis sp. strain SB2, and a Gammaproteobacteria methanotroph, Methylomicrobium album BG8. Mercury binding by methanobactin was evident in both the presence and absence of copper, despite the fact that methanobactin had a much higher affinity for copper due to the rapid and irreversible binding of mercury by methanobactin. The formation of a gray precipitate suggested that Hg(II), after being bound by methanobactin, was reduced to Hg(0) but was not volatilized. Rather, mercury remained associated with methanobactin and was also found associated with methanotrophic biomass. It thus appears that although the mercury-methanobactin complex was cell associated, mercury was not removed from methanobactin. The amount of biomass-associated mercury in the presence of methanobactin from M. trichosporium OB3b was greatest for M. trichosporium wild-type strain OB3b and the ΔmbnA mutant and least for M. album BG8, suggesting that methanotrophs may have selective methanobactin uptake systems that may be based on TonB-dependent transporters but that such uptake systems exhibit a degree of infidelity.
Collapse
|
27
|
Semrau JD, Jagadevan S, DiSpirito AA, Khalifa A, Scanlan J, Bergman BH, Freemeier BC, Baral BS, Bandow NL, Vorobev A, Haft DH, Vuilleumier S, Murrell JC. Methanobactin and MmoD work in concert to act as the 'copper-switch' in methanotrophs. Environ Microbiol 2013; 15:3077-86. [PMID: 23682956 DOI: 10.1111/1462-2920.12150] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 04/21/2013] [Indexed: 10/26/2022]
Abstract
Biological oxidation of methane to methanol by aerobic bacteria is catalysed by two different enzymes, the cytoplasmic or soluble methane monooxygenase (sMMO) and the membrane-bound or particulate methane monooxygenase (pMMO). Expression of MMOs is controlled by a 'copper-switch', i.e. sMMO is only expressed at very low copper : biomass ratios, while pMMO expression increases as this ratio increases. Methanotrophs synthesize a chalkophore, methanobactin, for the binding and import of copper. Previous work suggested that methanobactin was formed from a polypeptide precursor. Here we report that deletion of the gene suspected to encode for this precursor, mbnA, in Methylosinus trichosporium OB3b, abolishes methanobactin production. Further, gene expression assays indicate that methanobactin, together with another polypeptide of previously unknown function, MmoD, play key roles in regulating expression of MMOs. Based on these data, we propose a general model explaining how expression of the MMO operons is regulated by copper, methanobactin and MmoD. The basis of the 'copper-switch' is MmoD, and methanobactin amplifies the magnitude of the switch. Bioinformatic analysis of bacterial genomes indicates that the production of methanobactin-like compounds is not confined to methanotrophs, suggesting that its use as a metal-binding agent and/or role in gene regulation may be widespread in nature.
Collapse
Affiliation(s)
- Jeremy D Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA
| | - Sheeja Jagadevan
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, 48109-2125, USA
| | - Alan A DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Ashraf Khalifa
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.,Botany Department, Faculty of Science, Beni-Suef University, Beni-Suef, 65211, Egypt
| | - Julie Scanlan
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Brandt H Bergman
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Brittani C Freemeier
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Bipin S Baral
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Nathan L Bandow
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Alexey Vorobev
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, 48109-2125, USA
| | - Daniel H Haft
- J. Craig Venter Institute, 9704 Medical Center Drive, Rockville, MD, 20850, USA
| | - Stéphane Vuilleumier
- Equipe Adaptations et Interactions Microbiennes dans l'Environnement, Département Micro-organismes, Génomes, Environnement, UMR 7156 Université de Strasbourg - CNRS, Université de Strasbourg, 67083, Strasbourg Cédex, France
| | - J Colin Murrell
- School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| |
Collapse
|
28
|
Kenney GE, Rosenzweig AC. Genome mining for methanobactins. BMC Biol 2013; 11:17. [PMID: 23442874 PMCID: PMC3621798 DOI: 10.1186/1741-7007-11-17] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/26/2013] [Indexed: 01/27/2023] Open
Abstract
Background Methanobactins (Mbns) are a family of copper-binding natural products involved in copper uptake by methanotrophic bacteria. The few Mbns that have been structurally characterized feature copper coordination by two nitrogen-containing heterocycles next to thioamide groups embedded in a peptidic backbone of varying composition. Mbns are proposed to derive from post-translational modification of ribosomally synthesized peptides, but only a few genes encoding potential precursor peptides have been identified. Moreover, the relevance of neighboring genes in these genomes has been unclear. Results The potential for Mbn production in a wider range of bacterial species was assessed by mining microbial genomes. Operons encoding Mbn-like precursor peptides, MbnAs, were identified in 16 new species, including both methanotrophs and, surprisingly, non-methanotrophs. Along with MbnA, the core of the operon is formed by two putative biosynthetic genes denoted MbnB and MbnC. The species can be divided into five groups on the basis of their MbnA and MbnB sequences and their operon compositions. Additional biosynthetic proteins, including aminotransferases, sulfotransferases and flavin adenine dinucleotide (FAD)-dependent oxidoreductases were also identified in some families. Beyond biosynthetic machinery, a conserved set of transporters was identified, including MATE multidrug exporters and TonB-dependent transporters. Additional proteins of interest include a di-heme cytochrome c peroxidase and a partner protein, the roles of which remain a mystery. Conclusions This study indicates that Mbn-like compounds may be more widespread than previously thought, but are not present in all methanotrophs. This distribution of species suggests a broader role in metal homeostasis. These data provide a link between precursor peptide sequence and Mbn structure, facilitating predictions of new Mbn structures and supporting a post-translational modification biosynthetic pathway. In addition, testable models for Mbn transport and for methanotrophic copper regulation have emerged. Given the unusual modifications observed in Mbns characterized thus far, understanding the roles of the putative biosynthetic proteins is likely to reveal novel pathways and chemistry.
Collapse
Affiliation(s)
- Grace E Kenney
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | | |
Collapse
|
29
|
Ve T, Mathisen K, Helland R, Karlsen OA, Fjellbirkeland A, Røhr ÅK, Andersson KK, Pedersen RB, Lillehaug JR, Jensen HB. The Methylococcus capsulatus (Bath) secreted protein, MopE*, binds both reduced and oxidized copper. PLoS One 2012; 7:e43146. [PMID: 22916218 PMCID: PMC3423442 DOI: 10.1371/journal.pone.0043146] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 07/17/2012] [Indexed: 11/18/2022] Open
Abstract
Under copper limiting growth conditions the methanotrophic bacterium Methylococcus capsulatus (Bath) secrets essentially only one protein, MopE*, to the medium. MopE* is a copper-binding protein whose structure has been determined by X-ray crystallography. The structure of MopE* revealed a unique high affinity copper binding site consisting of two histidine imidazoles and one kynurenine, the latter an oxidation product of Trp130. In this study, we demonstrate that the copper ion coordinated by this strong binding site is in the Cu(I) state when MopE* is isolated from the growth medium of M. capsulatus. The conclusion is based on X-ray Near Edge Absorption spectroscopy (XANES), and Electron Paramagnetic Resonance (EPR) studies. EPR analyses demonstrated that MopE*, in addition to the strong copper-binding site, also binds Cu(II) at two weaker binding sites. Both Cu(II) binding sites have properties typical of non-blue type II Cu (II) centres, and the strongest of the two Cu(II) sites is characterised by a relative high hyperfine coupling of copper (A|| = 20 mT). Immobilized metal affinity chromatography binding studies suggests that residues in the N-terminal part of MopE* are involved in forming binding site(s) for Cu(II) ions. Our results support the hypothesis that MopE plays an important role in copper uptake, possibly making use of both its high (Cu(I) and low Cu(II) affinity properties.
Collapse
Affiliation(s)
- Thomas Ve
- Department of Molecular Biology, University of Bergen, Bergen, Norway
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia
| | - Karina Mathisen
- Department of Chemistry, Norwegian University of Science and Technology, Trondheim, Norway
| | - Ronny Helland
- Norwegian Structural Biology Centre, Faculty of Science, University of Tromso, Tromso, Norway
| | - Odd A. Karlsen
- Department of Molecular Biology, University of Bergen, Bergen, Norway
| | | | - Åsmund K. Røhr
- Department of Molecular Biosciences, University of Oslo, Oslo, Norway
| | | | - Rolf-Birger Pedersen
- Department of Earth Science–Centre for Geobiology, University of Bergen, Bergen, Norway
| | | | - Harald B. Jensen
- Department of Molecular Biology, University of Bergen, Bergen, Norway
- * E-mail:
| |
Collapse
|
30
|
Pesch ML, Christl I, Hoffmann M, Kraemer SM, Kretzschmar R. Copper complexation of methanobactin isolated from Methylosinus trichosporium OB3b: pH-dependent speciation and modeling. J Inorg Biochem 2012; 116:55-62. [PMID: 23010330 DOI: 10.1016/j.jinorgbio.2012.07.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 05/31/2012] [Accepted: 07/05/2012] [Indexed: 11/30/2022]
Abstract
Methanobactins are copper-binding ligands produced by aerobic methanotrophic microorganisms. A quantitative understanding of their potential role in methanotrophic copper acquisition requires the investigation of their copper complexes under relevant pH conditions. In this study, a chemical speciation model describing the pH-dependence of copper binding and the formation of the different complexes by methanobactin (mb) is released by Methylosinus trichosporium OB3b was developed. Potentiometric and spectrophotometric titrations of the free ligand indicated the presence of four protonation sites consistent with the molecular structure of methanobactin. Metal titrations revealed a distinct pH-dependence of copper binding to methanobactin between pH 5 and 8. Based on evidence from size-exclusion chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS), the copper binding was quantitatively described with three different types of copper-methanobactin complexes which can additionally undergo protonation reactions. The high affinity observed upon initial copper additions resulted from the predominant occurrence of copper-methanobactin dimer complexes, mb(2)H(4)Cu and mb(2)H(3)Cu with log K values of 58 and 52, respectively. With increasing copper to methanobactin ratios, methanobactin bound copper as monomers, mbHCu (log K=25) and mbCu (log K=18), whereas at elevated copper activities methanobactin was able to bind two copper ions (mbHCu(2) and mbCu(2)). Model calculations based on the fitted complexation constants suggest that in natural systems, copper-methanobactin complexes are mostly present as monomers.
Collapse
Affiliation(s)
- Marie-Laure Pesch
- Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, CHN, Universitätstrasse 16, 8092 Zurich, Switzerland
| | | | | | | | | |
Collapse
|
31
|
Variations in methanobactin structure influences copper utilization by methane-oxidizing bacteria. Proc Natl Acad Sci U S A 2012; 109:8400-4. [PMID: 22582172 DOI: 10.1073/pnas.1112921109] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Methane-oxidizing bacteria are nature's primary biological mechanism for suppressing atmospheric levels of the second-most important greenhouse gas via methane monooxygenases (MMOs). The copper-containing particulate enzyme is the most widespread and efficient MMO. Under low-copper conditions methane-oxidizing bacteria secrete the small copper-binding peptide methanobactin (mbtin) to acquire copper, but how variations in the structures of mbtins influence copper metabolism and species selection are unknown. Methanobactins have been isolated from Methylocystis strains M and hirsuta CSC1, organisms that can switch to using an iron-containing soluble MMO when copper is limiting, and the nonswitchover Methylocystis rosea. These mbtins are shorter, and have different amino acid compositions, than the characterized mbtin from Methylosinus trichosporium OB3b. A coordinating pyrazinedione ring in the Methylocystis mbtins has little influence on the Cu(I) site structure. The Methylocystis mbtins have a sulfate group that helps stabilize the Cu(I) forms, resulting in affinities of approximately 10(21) M(-1). The Cu(II) affinities vary over three orders of magnitude with reduction potentials covering approximately 250 mV, which may dictate the mechanism of intracellular copper release. Copper uptake and the switchover from using the iron-containing soluble MMO to the copper-containing particulate enzyme is faster when mediated by the native mbtin, suggesting that the amino acid sequence is important for the interaction of mbtins with receptors. The differences in structures and properties of mbtins, and their influence on copper utilization by methane-oxidizing bacteria, have important implications for the ecology and global function of these environmentally vital organisms.
Collapse
|
32
|
Bandow N, Gilles VS, Freesmeier B, Semrau JD, Krentz B, Gallagher W, McEllistrem MT, Hartsel SC, Choi DW, Hargrove MS, Heard TM, Chesner LN, Braunreiter KM, Cao BV, Gavitt MM, Hoopes JZ, Johnson JM, Polster EM, Schoenick BD, Umlauf AM, DiSpirito AA. Spectral and copper binding properties of methanobactin from the facultative methanotroph Methylocystis strain SB2. J Inorg Biochem 2012; 110:72-82. [DOI: 10.1016/j.jinorgbio.2012.02.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2011] [Revised: 01/06/2012] [Accepted: 02/01/2012] [Indexed: 11/25/2022]
|
33
|
Kenney GE, Rosenzweig AC. Chemistry and biology of the copper chelator methanobactin. ACS Chem Biol 2012; 7:260-8. [PMID: 22126187 DOI: 10.1021/cb2003913] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Methanotrophic bacteria, organisms that oxidize methane, produce a small copper chelating molecule called methanobactin (Mb). Mb binds Cu(I) with high affinity and is hypothesized to mediate copper acquisition from the environment. Recent advances in Mb characterization include revision of the chemical structure of Mb from Methylosinus trichosporium OB3b and further investigation of its biophysical properties. In addition, Mb production by several other methanotroph strains has been investigated, and preliminary characterization suggests diversity in chemical composition. Initial clues into Mb biosynthesis have been obtained by identification of a putative precursor gene in the M. trichosporium OB3b genome. Finally, direct uptake of intact Mb into the cytoplasm of M. trichosporium OB3b cells has been demonstrated, and studies of the transport mechanism have been initiated. Taken together, these advances represent significant progress and set the stage for exciting new research directions.
Collapse
Affiliation(s)
- Grace E. Kenney
- Departments of Molecular Biosciences
and of Chemistry, Northwestern University, Evanston, Illinois 60208,
United States
| | - Amy C. Rosenzweig
- Departments of Molecular Biosciences
and of Chemistry, Northwestern University, Evanston, Illinois 60208,
United States
| |
Collapse
|
34
|
Choi D, Sesham R, Kim Y, Angel LA. Analysis of methanobactin from Methylosinus trichosporium OB3b via ion mobility mass spectrometry. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2012; 18:509-520. [PMID: 23654196 DOI: 10.1255/ejms.1202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Methanobactins (mbs) are Low molecular mass copper binding chromopeptides analogous to pyoverdin class iron-binding siderophores. Mb produced by Methylosinus trichosporium OB3b (mb-oB3b) has been used as a model molecuLe for methanobactin although the amino acid sequence of mb-OB3b differs significantly from other characterized mbs. In particular, there is the presence of a pair of cystine residues which are absent in other characterized mbs. The role of the Cys3-Cys6 in copper binding, Cu(ll) reduction and its role on the mb-OB3b structure remains in debate. Here, we use a single-step dithiothreitol treatment as an effective method in reducing the disulfide bond allowing in-depth ion mobility-mass spectrometry (IM-MS) analysis. The IM-MS results show mb-oB3b exists in the gas-phase as three different negatively-charged states and exists in multiple conformational states, when introduced via electrospray ionization from aqueous solution near physiological pH. The disulfide bond serves a structural role and is not involved in the Cu(I/ll) binding capability of mb-OB3b, with the binding of a second Cu(I/ll) related to a further deprotonation of mb-OB3b. Overall, these findings are in good correlation with expected solution-phase behavior of mb-OB3b. The results suggest IM-MS is an effective tool for better understanding the complex nature of this intriguing peptide.
Collapse
Affiliation(s)
- DongWon Choi
- Department of BioLogical & Environmental Sciences, Texas A&M University-Commerce, 2600 S Neat St., Commerce. TX 75428, USA
| | | | | | | |
Collapse
|
35
|
Balasubramanian R, Kenney GE, Rosenzweig AC. Dual pathways for copper uptake by methanotrophic bacteria. J Biol Chem 2011; 286:37313-9. [PMID: 21900235 DOI: 10.1074/jbc.m111.284984] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Methanobactin (Mb), a 1217-Da copper chelator produced by the methanotroph Methylosinus trichosporium OB3b, is hypothesized to mediate copper acquisition from the environment, particularly from insoluble copper mineral sources. Although indirect evidence suggests that Mb provides copper for the regulation and activity of methane monooxygenase enzymes, experimental data for direct uptake of copper loaded Mb (Cu-Mb) are lacking. Uptake of intact Cu-Mb by M. trichosporium OB3b was demonstrated by isotopic and fluorescent labeling experiments. Confocal microscopy data indicate that Cu-Mb is localized in the cytoplasm. Both Cu-Mb and unchelated Cu are taken up by M. trichosporium OB3b, but by different mechanisms. Uptake of unchelated Cu is inhibited by spermine, suggesting a porin-dependent passive transport process. By contrast, uptake of Cu-Mb is inhibited by the uncoupling agents carbonyl cyanide m-chlorophenylhydrazone and methylamine, but not by spermine, consistent with an active transport process. Cu-Mb from M. trichosporium OB3b can also be internalized by other strains of methanotroph, but not by Escherichia coli, suggesting that Cu-Mb uptake is specific to methanotrophic bacteria. These findings are consistent with a key role for Cu-Mb in copper acquisition by methanotrophs and have important implications for further investigation of the copper uptake machinery.
Collapse
|
36
|
Karlsen OA, Larsen Ø, Jensen HB. The copper responding surfaceome of Methylococccus capsulatus Bath. FEMS Microbiol Lett 2011; 323:97-104. [DOI: 10.1111/j.1574-6968.2011.02365.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/05/2011] [Accepted: 07/11/2011] [Indexed: 11/28/2022] Open
Affiliation(s)
- Odd A. Karlsen
- Department of Molecular Biology; University of Bergen; Norway
| | | | | |
Collapse
|
37
|
Bandow NL, Gallagher WH, Behling L, Choi DW, Semrau JD, Hartsel SC, Gilles VS, Dispirito AA. Isolation of methanobactin from the spent media of methane-oxidizing bacteria. Methods Enzymol 2011; 495:259-69. [PMID: 21419927 DOI: 10.1016/b978-0-12-386905-0.00017-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chalkophores are low molecular mass modified peptides involved in copper acquisition in methane-oxidizing bacteria (MOB). A screening method for the detection of this copper-binding molecule is presented in Chapter 16. Here we describe methods to (1) maximize expression and secretion of chalkophores, (2) concentrate chalkophores from the spent media of MOB, and (3) purify chalkophores.
Collapse
Affiliation(s)
- Nathan L Bandow
- Department of Biochemistry, Iowa State University, Ames, Iowa, USA
| | | | | | | | | | | | | | | |
Collapse
|
38
|
|
39
|
Krentz BD, Mulheron HJ, Semrau JD, Dispirito AA, Bandow NL, Haft DH, Vuilleumier S, Murrell JC, McEllistrem MT, Hartsel SC, Gallagher WH. A comparison of methanobactins from Methylosinus trichosporium OB3b and Methylocystis strain Sb2 predicts methanobactins are synthesized from diverse peptide precursors modified to create a common core for binding and reducing copper ions. Biochemistry 2010; 49:10117-30. [PMID: 20961038 DOI: 10.1021/bi1014375] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Methanobactins (mb) are low-molecular mass, copper-binding molecules secreted by most methanotrophic bacteria. These molecules have been identified for a number of methanotrophs, but only the one produced by Methylosinus trichosporium OB3b (mb-OB3b) has to date been chemically characterized. Here we report the chemical characterization and copper binding properties of a second methanobactin, which is produced by Methylocystis strain SB2 (mb-SB2). mb-SB2 shows some significant similarities to mb-OB3b, including its spectral and metal binding properties, and its ability to bind and reduce Cu(II) to Cu(I). Like mb-OB3b, mb-SB2 contains two five-member heterocyclic rings with associated enethiol groups, which together form the copper ion binding site. mb-SB2 also displays some significant differences compared to mb-OB3b, including the number and types of amino acids used to complete the structure of the molecule, the presence of an imidazolone ring in place of one of the oxazolone rings found in mb-OB3b, and the presence of a sulfate group not found in mb-OB3b. The sulfate is bonded to a threonine-like side chain that is associated with one of the heterocyclic rings and may represent the first example of this type of sulfate group found in a bacterially derived peptide. Acid-catalyzed hydrolysis and decarboxylation of the oxazolone rings found in mb-OB3b and mb-SB2 produce pairs of amino acid residues and suggest that both mb-OB3b and mb-SB2 are derived from peptides. In support of this, the gene for a ribosomally produced peptide precursor for mb-OB3b has been identified in the genome of M. trichosporium OB3b. The gene sequence indicates that the oxazolone rings in mb-OB3b are derived from the combination of a cysteine residue and the carbonyl from the preceding residue in the peptide sequence. Taken together, the results suggest methanobactins make up a structurally diverse group of ribosomally produced, peptide-derived molecules, which share a common pair of five-member rings with associated enethiol groups that are able to bind, reduce, and stabilize copper ions in an aqueous environment.
Collapse
Affiliation(s)
- Benjamin D Krentz
- Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702-4004, United States
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|