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Yao Y, He J, Chen F, Dong M. Arsinothricin Biosynthesis Involving a Radical SAM Enzyme for Noncanonical SAM Cleavage and C-As Bond Formation. J Am Chem Soc 2024; 146:21214-21219. [PMID: 39052934 DOI: 10.1021/jacs.4c06403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2024]
Abstract
Arsinothricin is a potent antibiotic secreted by soil bacteria. The biosynthesis of arsinothricin was proposed to involve a C-As bond formation between trivalent As and the 3-amino-3-carboxypropyl (ACP) group of S-adenosyl-l-methionine (SAM), which is catalyzed by the protein ArsL. However, ArsL has not been characterized in detail. Interestingly, ArsL contains a CxxxCxxC motif and thus belongs to the radical SAM enzyme superfamily, the members of which cleave SAM and generate a 5'-deoxyadenosyl radical. Here, we found that ArsL cleaves the Cγ,Met-S bond of SAM and generates an ACP radical that resembles Dph2, a noncanonical radical SAM enzyme involved in diphthamid biosynthesis. As Dph2 does not contain the CxxxCxxC motif, ArsL is a unique radical SAM enzyme that contains this motif but generates a noncanonical ACP radical. Together with the methyltransferase ArsM, we successfully reconstituted arsinothricin biosynthesis in vitro. ArsL has a conserved RCCLKC motif in the C-terminal sequence and belongs to the RCCLKC-tail radical SAM protein subfamily. By truncation and mutagenesis, we showed that this motif plays an important role in binding to the substrate arsenite and is highly important for its activity. Our results suggested that ArsL has a canonical radical SAM enzyme motif but catalyzes a noncanonical radical SAM reaction, implying that more noncanonical radical SAM chemistry may exist within the radical SAM enzyme superfamily.
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Affiliation(s)
- Yadi Yao
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Jiale He
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Fan Chen
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Min Dong
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
- Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China
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2
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Bhat A, Sharma R, Desigan K, Lucas MM, Mishra A, Bowers RM, Woyke T, Epstein B, Tiffin P, Pueyo JJ, Paape T. Horizontal gene transfer of the Mer operon is associated with large effects on the transcriptome and increased tolerance to mercury in nitrogen-fixing bacteria. BMC Microbiol 2024; 24:247. [PMID: 38971740 PMCID: PMC11227200 DOI: 10.1186/s12866-024-03391-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Accepted: 06/19/2024] [Indexed: 07/08/2024] Open
Abstract
BACKGROUND Mercury (Hg) is highly toxic and has the potential to cause severe health problems for humans and foraging animals when transported into edible plant parts. Soil rhizobia that form symbiosis with legumes may possess mechanisms to prevent heavy metal translocation from roots to shoots in plants by exporting metals from nodules or compartmentalizing metal ions inside nodules. Horizontal gene transfer has potential to confer immediate de novo adaptations to stress. We used comparative genomics of high quality de novo assemblies to identify structural differences in the genomes of nitrogen-fixing rhizobia that were isolated from a mercury (Hg) mine site that show high variation in their tolerance to Hg. RESULTS Our analyses identified multiple structurally conserved merA homologs in the genomes of Sinorhizobium medicae and Rhizobium leguminosarum but only the strains that possessed a Mer operon exhibited 10-fold increased tolerance to Hg. RNAseq analysis revealed nearly all genes in the Mer operon were significantly up-regulated in response to Hg stress in free-living conditions and in nodules. In both free-living and nodule environments, we found the Hg-tolerant strains with a Mer operon exhibited the fewest number of differentially expressed genes (DEGs) in the genome, indicating a rapid and efficient detoxification of Hg from the cells that reduced general stress responses to the Hg-treatment. Expression changes in S. medicae while in bacteroids showed that both rhizobia strain and host-plant tolerance affected the number of DEGs. Aside from Mer operon genes, nif genes which are involved in nitrogenase activity in S. medicae showed significant up-regulation in the most Hg-tolerant strain while inside the most Hg-accumulating host-plant. Transfer of a plasmid containing the Mer operon from the most tolerant strain to low-tolerant strains resulted in an immediate increase in Hg tolerance, indicating that the Mer operon is able to confer hyper tolerance to Hg. CONCLUSIONS Mer operons have not been previously reported in nitrogen-fixing rhizobia. This study demonstrates a pivotal role of the Mer operon in effective mercury detoxification and hypertolerance in nitrogen-fixing rhizobia. This finding has major implications not only for soil bioremediation, but also host plants growing in mercury contaminated soils.
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Affiliation(s)
- Aditi Bhat
- Brookhaven National Laboratory, Upton, USA
| | | | | | | | - Ankita Mishra
- Institute for Advancing Health Through Agriculture, Texas A&M, College Station, TX, USA
| | - Robert M Bowers
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Tanja Woyke
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Brendan Epstein
- Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - Peter Tiffin
- Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA
| | - José J Pueyo
- Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Tim Paape
- Institute for Advancing Health Through Agriculture, Texas A&M, College Station, TX, USA.
- USDA-ARS Children's Nutrition Research Center, Houston, TX, USA.
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Chua JS, Rajasabhai R, Teo WZ, Xue B, Yew WS. Engineering a Metal Reductase for the Bioremediation of Anthropogenic Electronic Wastes: From Hg(II) to Au(III) and Ag(I) Enzymatic Reduction. JACS AU 2024; 4:2335-2342. [PMID: 38938813 PMCID: PMC11200239 DOI: 10.1021/jacsau.4c00297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 05/23/2024] [Accepted: 05/24/2024] [Indexed: 06/29/2024]
Abstract
Recovering precious metals from electronic waste (e-waste) using microbes presents a sustainable methodology that can contribute toward the maintenance of planetary health. To better realize the potential of bioremediation using engineered microbes, enzymes that mediate the reduction of Au(III) to Au(0) have been the subject of intense research. In this study, we report the successful engineering of a metal reductase, MerA, whose cognate substrate is mercury(II), toward other precious metals such as Au(III) and Ag(I). The engineered variant, G415I, exhibited a 15-fold increase in catalytic efficiency (k cat/K M) in Au(III) reduction to Au(0) and a 200-fold increase in catalytic efficiency in Ag(I) reduction to Ag(0) with respect to the wild-type enzyme. The apparent shift in preference toward noncognate metal ions may be attributed to the energetics of valency preference. The improved Au(III) reductase has an apparent increased preference toward monovalent cations such as Au(I) and Ag(I), with respect to divalent cations such as Hg(II), the cognate substrate of the progenitor MerA (an increase in K M of 5.0-fold for Hg(II), compared to a decrease in K M of 5.8-fold for Au(III) and 1.8-fold for Ag(I), respectively). This study further extends the mechanistic understanding of Au(III) bioreduction that could proceed through the stabilization of Au(I) en route to Au(0) and suggests that the biosynthesis of Au nanoparticles with high efficiency can be realized through the engineering of promiscuous metal reductases for precious metal recovery from e-wastes.
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Affiliation(s)
- Jasmine
Puay Suan Chua
- Department
of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- NUS
Synthetic Biology for Clinical and Technological Innovation, 28 Medical Drive, Singapore 117456, Singapore
- Synthetic
Biology Translational Research Programme, Yong Loo Lin School of Medicine, National University of Singapore, 14 Medical Drive, Singapore 117599, Singapore
| | - Rashmi Rajasabhai
- Department
of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- NUS
Synthetic Biology for Clinical and Technological Innovation, 28 Medical Drive, Singapore 117456, Singapore
| | - Wei Zhe Teo
- Department
of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- NUS
Synthetic Biology for Clinical and Technological Innovation, 28 Medical Drive, Singapore 117456, Singapore
- Synthetic
Biology Translational Research Programme, Yong Loo Lin School of Medicine, National University of Singapore, 14 Medical Drive, Singapore 117599, Singapore
| | - Bo Xue
- Department
of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- NUS
Synthetic Biology for Clinical and Technological Innovation, 28 Medical Drive, Singapore 117456, Singapore
- Synthetic
Biology Translational Research Programme, Yong Loo Lin School of Medicine, National University of Singapore, 14 Medical Drive, Singapore 117599, Singapore
| | - Wen Shan Yew
- Department
of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), 8 Medical Drive, Singapore 117597, Singapore
- NUS
Synthetic Biology for Clinical and Technological Innovation, 28 Medical Drive, Singapore 117456, Singapore
- Synthetic
Biology Translational Research Programme, Yong Loo Lin School of Medicine, National University of Singapore, 14 Medical Drive, Singapore 117599, Singapore
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4
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Bonanata J. The role of the active site lysine residue on FAD reduction by NADPH in glutathione reductase. Comput Biol Chem 2024; 110:108075. [PMID: 38678729 DOI: 10.1016/j.compbiolchem.2024.108075] [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: 11/22/2023] [Revised: 04/01/2024] [Accepted: 04/11/2024] [Indexed: 05/01/2024]
Abstract
Glutathione reductase (GR) is a two dinucleotide binding domain flavoprotein (tDBDF) that catalyzes the reduction of glutathione disulfide to glutathione coupled to the oxidation of NADPH to NADP+. An interesting feature of GR and other tDBDFs is the presence of a lysine residue (Lys-66 in human GR) at the active site, which interacts with the flavin group, but has an unknown function. To better understand the role of this residue, the dynamics of GR was studied using molecular dynamics simulations, and the reaction mechanism of FAD reduction by NADPH was studied using QM/MM molecular modeling. The two possible protonation states of Lys-66 were considered: neutral and protonated. Molecular dynamics results suggest that the active site is more structured for neutral Lys-66 than for protonated Lys-66. QM/MM modeling results suggest that Lys-66 should be in its neutral state for a thermodynamically favorable reduction of FAD by NADPH. Since the reaction is unfavorable with protonated Lys-66, the reverse reaction (the reduction of NADP+ by FADH-) is expected to take place. A phylogenetic analysis of various tDBDFs was performed, finding that an active site lysine is present in different the tDBDFs enzymes, suggesting that it has a conserved biological role. Overall, these results suggest that the protonation state of the active site lysine determines the energetics of the reaction, controlling its reversibility.
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Affiliation(s)
- Jenner Bonanata
- Laboratorio de Química Teórica y Computacional, Instituto de Química Biológica, Facultad de Ciencias, Universidad de la República, Uruguay; Centro de Investigaciones Biomédicas, Universidad de la República, Uruguay.
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5
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Smith MM, Moran GR. Building on a theme: The redox hierarchy of pyridine nucleotide-disulfide oxidoreductases. Arch Biochem Biophys 2024; 755:109966. [PMID: 38537870 DOI: 10.1016/j.abb.2024.109966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Revised: 03/14/2024] [Accepted: 03/21/2024] [Indexed: 04/24/2024]
Abstract
Flavin disulfide reductases (FDRs) are FAD-dependent enzymes that transmit electrons from NAD(P)H to reduce specific oxidant substrate disulfides. These enzymes have been studied extensively, most particularly the paradigm examples: glutathione reductase and thioredoxin reductase. The common, though not universal, traits of the family include a tyrosine- or phenylalanine-gated binding pocket for NAD(P) nicotinamides adjacent to the FAD isoalloxazine re-face, and a disulfide stacked against the si-face of the isoalloxazine whose dithiol form is activated for subsequent exchange reactions by a nearby histidine acting as a base. This arrangement promotes transduction of the reducing equivalents for disulfide exchange relay reactions. From an observational standpoint the proximal parallel stacking of three redox moieties induces up to three opportunities for unique charge transfer interactions (NAD(P)H FAD, NAD(P)+•FADH2, and FAD•thiolate). In transient state, the charge transfer transitions provide discrete signals to assign reaction sequences. This review summarizes the lineage of observations for the FDR enzymes that have been extensively studied. Where applicable and in order to chart a consistent interpretation of the record, only data derived from studies that used anaerobic methods are cited. These data reveal a recurring theme for catalysis that is elaborated with specific additional functionalities for each oxidant substrate.
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Affiliation(s)
- Madison M Smith
- Department of Chemistry and Biochemistry, 1068 W Sheridan Rd, Loyola University Chicago, Chicago, IL, 60660, United States
| | - Graham R Moran
- Department of Chemistry and Biochemistry, 1068 W Sheridan Rd, Loyola University Chicago, Chicago, IL, 60660, United States.
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6
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Gutiérrez-Fernández J, Hersleth HP, Hammerstad M. The crystal structure of mycothiol disulfide reductase (Mtr) provides mechanistic insight into the specific low-molecular-weight thiol reductase activity of Actinobacteria. Acta Crystallogr D Struct Biol 2024; 80:181-193. [PMID: 38372589 PMCID: PMC10910545 DOI: 10.1107/s205979832400113x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Accepted: 02/01/2024] [Indexed: 02/20/2024] Open
Abstract
Low-molecular-weight (LMW) thiols are involved in many processes in all organisms, playing a protective role against reactive species, heavy metals, toxins and antibiotics. Actinobacteria, such as Mycobacterium tuberculosis, use the LMW thiol mycothiol (MSH) to buffer the intracellular redox environment. The NADPH-dependent FAD-containing oxidoreductase mycothiol disulfide reductase (Mtr) is known to reduce oxidized mycothiol disulfide (MSSM) to MSH, which is crucial to maintain the cellular redox balance. In this work, the first crystal structures of Mtr are presented, expanding the structural knowledge and understanding of LMW thiol reductases. The structural analyses and docking calculations provide insight into the nature of Mtrs, with regard to the binding and reduction of the MSSM substrate, in the context of related oxidoreductases. The putative binding site for MSSM suggests a similar binding to that described for the homologous glutathione reductase and its respective substrate glutathione disulfide, but with distinct structural differences shaped to fit the bulkier MSSM substrate, assigning Mtrs as uniquely functioning reductases. As MSH has been acknowledged as an attractive antitubercular target, the structural findings presented in this work may contribute towards future antituberculosis drug development.
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Affiliation(s)
- Javier Gutiérrez-Fernández
- Section for Biochemistry and Molecular Biology, Department of Biosciences, University of Oslo, PO Box 1066, Blindern, 0316 Oslo, Norway
- Centre for Molecular Medicine Norway, Nordic EMBL Partnership, University of Oslo, 0318 Oslo, Norway
| | - Hans-Petter Hersleth
- Section for Biochemistry and Molecular Biology, Department of Biosciences, University of Oslo, PO Box 1066, Blindern, 0316 Oslo, Norway
| | - Marta Hammerstad
- Section for Biochemistry and Molecular Biology, Department of Biosciences, University of Oslo, PO Box 1066, Blindern, 0316 Oslo, Norway
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7
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Shin H, Baek Y, Lee D, Xu Y, Kwon Y, Jo I, Ha NC. Structural and Functional Analyses of the Flavoprotein Disulfide Reductase FN0820 of Fusobacterium nucleatum. J Microbiol 2023; 61:1033-1041. [PMID: 38117463 DOI: 10.1007/s12275-023-00095-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 11/07/2023] [Accepted: 11/07/2023] [Indexed: 12/21/2023]
Abstract
Escherichia coli RclA and Staphylococcus aureus MerA are part of the Group I flavoprotein disulfide reductase (FDR) family and have been implicated in the contribution to bacterial pathogenesis by defending against the host immune response. Fusobacterium nucleatum is a pathogenic, anaerobic Gram-negative bacterial species commonly found in the human oral cavity and gastrointestinal tract. In this study, we discovered that the F. nucleatum protein FN0820, belonging to the Group I FDR family, exhibited a higher activity of a Cu2+-dependent NADH oxidase than E. coli RclA. Moreover, FN0820 decreased the dissolved oxygen level in the solution with higher NADH oxidase activity. We found that L-tryptophan and its analog 5-hydroxytryptophan inhibit the FN0820 activities of NADH oxidase and the concomitant reduction of oxygen. Our results have implications for developing new treatment strategies against pathogens that defend the host immune response with Group I FDRs.
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Affiliation(s)
- Hyunwoo Shin
- Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, CALS, Seoul National University, Seoul, 08826, Republic of Korea
| | - Yeongjin Baek
- Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, CALS, Seoul National University, Seoul, 08826, Republic of Korea
| | - Dukwon Lee
- Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, CALS, Seoul National University, Seoul, 08826, Republic of Korea
| | - Yongbin Xu
- Department of Bioengineering, College of Life Science, Dalian Minzu University, Dalian, 116600, People's Republic of China
| | - Yonghoon Kwon
- Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, CALS, Seoul National University, Seoul, 08826, Republic of Korea
| | - Inseong Jo
- Infectious Diseases Therapeutic Research Center, Korea Research Institute of Chemical Technology (KRICT), Daejeon, 34114, Republic of Korea.
| | - Nam-Chul Ha
- Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, CALS, Seoul National University, Seoul, 08826, Republic of Korea.
- Center for Food and Bioconvergence, Seoul National University, Seoul, 08826, Republic of Korea.
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8
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Mascarenhas R, Guha A, Li Z, Ruetz M, An S, Seravalli J, Banerjee R. Cobalt-Sulfur Coordination Chemistry Drives B 12 Loading onto Methionine Synthase. J Am Chem Soc 2023:10.1021/jacs.3c07941. [PMID: 37916782 PMCID: PMC11063128 DOI: 10.1021/jacs.3c07941] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2023]
Abstract
Cobalt-sulfur (Co-S) coordination is labile to both oxidation and reduction chemistry and is rarely seen in nature. Cobalamin (or vitamin B12) is an essential cobalt-containing organometallic cofactor in mammals and is escorted via an intricate network of chaperones to a single cytoplasmic target, methionine synthase. In this study, we report that the human cobalamin trafficking protein, MMADHC, exploits the chemical lability of Co-S coordination for cofactor off-loading onto methionine synthase. Cys-261 on MMADHC serves as the β-axial ligand to cobalamin. Complex formation between MMADHC and methionine synthase is signaled by loss of the lower axial nitrogen ligand, leading to five-coordinate thiolato-cobalamin. Nucleophilic displacement by the vicinal thiolate, Cys-262, completes cofactor transfer to methionine synthase and release of a cysteine disulfide-containing MMADHC. The physiological relevance of this mechanism is supported by clinical variants of MMADHC, which impair cofactor binding and off-loading, explaining the molecular basis of the associated homocystinuria.
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Affiliation(s)
- Romila Mascarenhas
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Arkajit Guha
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Zhu Li
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Markus Ruetz
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Sojin An
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Javier Seravalli
- Department of Biological Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Ruma Banerjee
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
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9
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Pardhe BD, Lee MJ, Lee JH, Do H, Oh TJ. Biochemical and structural basis of mercuric reductase, GbsMerA, from Gelidibacter salicanalis PAMC21136. Sci Rep 2023; 13:17854. [PMID: 37857791 PMCID: PMC10587081 DOI: 10.1038/s41598-023-44968-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2023] [Accepted: 10/13/2023] [Indexed: 10/21/2023] Open
Abstract
Heavy metals, including mercury, are non-biodegradable and highly toxic to microorganisms even at low concentrations. Understanding the mechanisms underlying the environmental adaptability of microorganisms with Hg resistance holds promise for their use in Hg bioremediation. We characterized GbsMerA, a mercury reductase belonging to the mercury-resistant operon of Gelidibacter salicanalis PAMC21136, and found its maximum activity of 474.7 µmol/min/mg in reducing Hg+2. In the presence of Ag and Mn, the enzyme exhibited moderate activity as 236.5 µmol/min/mg and 69 µmol/min/mg, respectively. GbsMerA exhibited optimal activity at pH 7.0 and a temperature of 60 °C. Moreover, the crystal structure of GbsMerA and structural comparison with homologues indicated that GbsMerA contains residues, Tyr437´ and Asp47, which may be responsible for metal transfer at the si-face by providing a hydroxyl group (-OH) to abstract a proton from the thiol group of cysteine. The complex structure with NADPH indicated that Y174 in the re-face can change its side chain direction upon NADPH binding, indicating that Y174 may have a role as a gate for NADPH binding. Moreover, the heterologous host expressing GbsMerA (pGbsMerA) is more resistant to Hg toxicity when compared to the host lacking GbsMerA. Overall, this study provides a background for understanding the catalytic mechanism and Hg detoxification by GbsMerA and suggests the application of genetically engineered E. coli strains for environmental Hg removal.
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Affiliation(s)
- Bashu Dev Pardhe
- Department of Life Science and Biochemical Engineering, Graduate School, SunMoon University, Asan, 31460, Republic of Korea
| | - Min Ju Lee
- Research Unit of Cryogenic Novel Material, Korea Polar Research Institute, Incheon, 21990, Republic of Korea
| | - Jun Hyuck Lee
- Research Unit of Cryogenic Novel Material, Korea Polar Research Institute, Incheon, 21990, Republic of Korea
- Department of Polar Sciences, University of Science and Technology, Incheon, 21990, Republic of Korea
| | - Hackwon Do
- Research Unit of Cryogenic Novel Material, Korea Polar Research Institute, Incheon, 21990, Republic of Korea.
- Department of Polar Sciences, University of Science and Technology, Incheon, 21990, Republic of Korea.
| | - Tae-Jin Oh
- Department of Life Science and Biochemical Engineering, Graduate School, SunMoon University, Asan, 31460, Republic of Korea.
- Genome-Based BioIT Convergence Institute, Asan, 31460, Republic of Korea.
- Department of Pharmaceutical Engineering and Biotechnology, SunMoon University, Asan, 31460, Republic of Korea.
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10
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Bernabeu de Maria M, Tesauro D, Prencipe F, Saviano M, Messori L, Enjalbal C, Lobinski R, Ronga L. Disclosing the Preferential Mercury Chelation by SeCys Containing Peptides over Their Cys Analogues. Inorg Chem 2023; 62:14980-14990. [PMID: 37651565 DOI: 10.1021/acs.inorgchem.3c01708] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
Methylmercury, mercury (II), and mercury (I) chlorides were found to react with vasopressin, a nonapeptide hormone cyclized by two cysteine residues, and its mono- and diselenium analogues to form several mercury-peptide adducts. The replacement of Cys by SeCys in vasopressin increased the reactivity toward methylmercury, with the predominant formation of -Se/S-Hg-Se-bridged structures and the consequent demethylation of methylmercury. In competitive experiments, CH3HgCl reacted preferentially with the diselenium analogue rather than with vasopressin. The diselenium peptide also showed the capability to displace the CH3Hg moiety bound to S in vasopressin. These results open a promising perspective for the use of selenopeptides for methylmercury chelation and detoxification strategies.
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Affiliation(s)
| | - Diego Tesauro
- Department of Pharmacy and CIRPeB, Università Degli Studi di Napoli Federico II, 49 80131 Naples, Italy
| | | | | | - Luigi Messori
- Department of Chemistry, Università Degli Studi di Firenze, 50019 Sesto Fiorentino, Italy
| | - Christine Enjalbal
- IBMM, Université de Montpellier, CNRS, ENSCM, UMR 5247, 34293 Montpellier Cedex 5, France
| | - Ryszard Lobinski
- Pays de l'Adour, E2S UPPA, CNRS, IPREM, 64000 Pau, France
- Warsaw University of Technology, 00-664 Warsaw, Poland
| | - Luisa Ronga
- Pays de l'Adour, E2S UPPA, CNRS, IPREM, 64000 Pau, France
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11
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Singh S, Kumar V, Gupta P, Ray M. The trafficking of Hg II by alleviating its toxicity via Citrobacter sp. IITISM25 in batch and pilot-scale investigation. JOURNAL OF HAZARDOUS MATERIALS 2022; 433:128711. [PMID: 35395524 DOI: 10.1016/j.jhazmat.2022.128711] [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: 12/29/2021] [Revised: 03/10/2022] [Accepted: 03/13/2022] [Indexed: 06/14/2023]
Abstract
The study aims to see how effective the Citrobacter species strain is in removing HgII under stressful conditions. For this, a response surface methodology was chosen to optimized pH, temperature, and biomass for effective biotransformation of HgII. The optimized value for pH, temperature, and biomass were 6.5, 30 °C, and 2 mg/l with 89% HgII removal potential. TEM-EDX showed accumulated mercury onto the bacterial surface. Pot study was conducted to check the potentiality of this strain in alleviating the toxicity in Solanum lycopersicum L. under different concentrations of mercury. The enhancement in antioxidative enzymes, as well as mercury accumulation, was observed in test plants inoculated with IITISM25. Obtained result showed a greater accumulation of mercury in the root system than that of the shoot system due to poor translocation. Moreover, mercury reductase enzyme synthesis was also boosted by the addition of β-mercaptoethanol and L-cysteine. The optimized condition for maximum enzyme synthesis was at pH 7.5 and temperature 30 °C with Km = 48.07 μmol and Vmax = 9.75 μmol/min. Thus, we can say that Citrobacter species strain IITISM25 can be effectively applied in remediation of HgII stress condition as well as promotion of Solanum lycopersicum L growth under stress conditions as a promising host.
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Affiliation(s)
- Shalini Singh
- Laboratory of Applied Microbiology, Department of Environmental Science & Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826 004, Jharkhand, India
| | - Vipin Kumar
- Laboratory of Applied Microbiology, Department of Environmental Science & Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826 004, Jharkhand, India.
| | - Pratishtha Gupta
- Laboratory of Applied Microbiology, Department of Environmental Science & Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826 004, Jharkhand, India
| | - Madhurya Ray
- Laboratory of Applied Microbiology, Department of Environmental Science & Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826 004, Jharkhand, India
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Christakis CA, Barkay T, Boyd ES. Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea. Front Microbiol 2021; 12:682605. [PMID: 34248899 PMCID: PMC8261052 DOI: 10.3389/fmicb.2021.682605] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Accepted: 05/28/2021] [Indexed: 11/13/2022] Open
Abstract
Mercury (Hg) is a highly toxic element due to its high affinity for protein sulfhydryl groups, which upon binding, can destabilize protein structure and decrease enzyme activity. Prokaryotes have evolved enzymatic mechanisms to detoxify inorganic Hg and organic Hg (e.g., MeHg) through the activities of mercuric reductase (MerA) and organomercury lyase (MerB), respectively. Here, the taxonomic distribution and evolution of MerAB was examined in 84,032 archaeal and bacterial genomes, metagenome assembled genomes, and single-cell genomes. Homologs of MerA and MerB were identified in 7.8 and 2.1% percent of genomes, respectively. MerA was identified in the genomes of 10 archaeal and 28 bacterial phyla previously unknown to code for this functionality. Likewise, MerB was identified in 2 archaeal and 11 bacterial phyla previously unknown to encode this functionality. Surprisingly, homologs of MerB were identified in a number of genomes (∼50% of all MerB-encoding genomes) that did not encode MerA, suggesting alternative mechanisms to detoxify Hg(II) once it is generated in the cytoplasm. Phylogenetic reconstruction of MerA place its origin in thermophilic Thermoprotei (Crenarchaeota), consistent with high levels of Hg(II) in geothermal environments, the natural habitat of this archaeal class. MerB appears to have been recruited to the mer operon relatively recently and likely among a mesophilic ancestor of Euryarchaeota and Thaumarchaeota. This is consistent with the functional dependence of MerB on MerA and the widespread distribution of mesophilic microorganisms that methylate Hg(II) at lower temperature. Collectively, these results expand the taxonomic and ecological distribution of mer-encoded functionalities, and suggest that selection for Hg(II) and MeHg detoxification is dependent not only on the availability and type of mercury compounds in the environment but also the physiological potential of the microbes who inhabit these environments. The expanded diversity and environmental distribution of MerAB identify new targets to prioritize for future research.
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Affiliation(s)
- Christos A. Christakis
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT, United States
| | - Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States
| | - Eric S. Boyd
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT, United States
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Manceau A, Nagy KL, Glatzel P, Bourdineaud JP. Acute Toxicity of Divalent Mercury to Bacteria Explained by the Formation of Dicysteinate and Tetracysteinate Complexes Bound to Proteins in Escherichia coli and Bacillus subtilis. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:3612-3623. [PMID: 33629845 DOI: 10.1021/acs.est.0c05202] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Bacteria are the most abundant organisms on Earth and also the major life form affected by mercury (Hg) poisoning in aquatic and terrestrial food webs. In this study, we applied high energy-resolution X-ray absorption near edge structure (HR-XANES) spectroscopy to bacteria with intracellular concentrations of Hg as low as 0.7 ng/mg (ppm) for identifying the intracellular molecular forms and trafficking pathways of Hg in bacteria at environmentally relevant concentrations. Gram-positive Bacillus subtilis and Gram-negative Escherichia coli were exposed to three Hg species: HgCl2, Hg-dicysteinate (Hg(Cys)2), and Hg-dithioglycolate (Hg(TGA)2). In all cases, Hg was transformed into new two- and four-coordinate cysteinate complexes, interpreted to be bound, respectively, to the consensus metal-binding CXXC motif and zinc finger domains of proteins, with glutathione acting as a transfer ligand. Replacement of zinc cofactors essential to gene regulatory proteins with Hg would inhibit vital functions such as DNA transcription and repair and is suggested to be a main cause of Hg genotoxicity.
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Affiliation(s)
- Alain Manceau
- Université Grenoble Alpes, CNRS, ISTerre, CS 40700, 38058 Grenoble, France
| | - Kathryn L Nagy
- Department of Earth and Environmental Sciences, University of Illinois at Chicago, MC-186, 845 West Taylor Street, Chicago, Illinois 60607, United States
| | - Pieter Glatzel
- European Synchrotron Radiation Facility (ESRF), 71 Rue des Martyrs, 38000 Grenoble, France
| | - Jean-Paul Bourdineaud
- Institut Européen de Chimie et Biologie, Université de Bordeaux, CNRS, UMR 5234, 2 rue Escarpit, 33607 Pessac, France
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Overview of structurally homologous flavoprotein oxidoreductases containing the low M r thioredoxin reductase-like fold - A functionally diverse group. Arch Biochem Biophys 2021; 702:108826. [PMID: 33684359 DOI: 10.1016/j.abb.2021.108826] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 02/23/2021] [Accepted: 02/27/2021] [Indexed: 01/12/2023]
Abstract
Structural studies show that enzymes have a limited number of unique folds, although structurally related enzymes have evolved to perform a large variety of functions. In this review, we have focused on enzymes containing the low molecular weight thioredoxin reductase (low Mr TrxR) fold. This fold consists of two domains, both containing a three-layer ββα sandwich Rossmann-like fold, serving as flavin adenine dinucleotide (FAD) and, in most cases, pyridine nucleotide (NAD(P)H) binding-domains. Based on a search of the Protein Data Bank for all published structures containing the low Mr TrxR-like fold, we here present a comprehensive overview of enzymes with this structural architecture. These range from TrxR-like ferredoxin/flavodoxin NAD(P)+ oxidoreductases, through glutathione reductase, to NADH peroxidase. Some enzymes are solely composed of the low Mr TrxR-like fold, while others contain one or two additional domains. In this review, we give a detailed description of selected enzymes containing only the low Mr TrxR-like fold, however, catalyzing a diversity of chemical reactions. Our overview of this structurally similar, yet functionally distinct group of flavoprotein oxidoreductases highlights the fascinating and increasing number of studies describing the diversity among these enzymes, especially during the last decade(s).
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Reddy KKA, Jayashree M, Govindu PCV, Gowd KH. Ligand-induced transition in conformations of vicinal cysteine disulfides in proteins. Proteins 2020; 89:599-613. [PMID: 33378101 DOI: 10.1002/prot.26039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Revised: 11/04/2020] [Accepted: 12/12/2020] [Indexed: 01/02/2023]
Abstract
Vicinal cysteine disulfides are thought to be associated with specific conformations of cysteine disulfides due to the restricted rotation of single bonds in an eight-membered cyclic disulfide loop. Conformations of vicinal cysteine disulfides are analyzed using χ1 , χ2 , χ3 , χ2 ', χ1 ' torsion angles in the crystal structures of proteins retrieved from Protein Data Bank (PDB). 85% of vicinal disulfides have (+, -)LHStaple conformation with trans configuration of the peptide bond and 9% have (-, -)RHStaple conformation with cis configured peptide bond. Conformational analysis of dipeptide Cys-Cys vicinal disulfide by density functional theory (DFT) further supported (+, -)LHStaple, (-, -)RHStaple, and (+, +)RHStaple as the preferred conformations of vicinal disulfides. Interestingly, the rare conformations of vicinal disulfides are observed in the ligand-bound forms of proteins and have higher disulfide strain energy. Conformations of vicinal disulfides in palmitoyl protein thioesterase 1, AChBP, and α7 nicotinic receptor are changed from preferred (+, -)LHStaple to rare (+, -)AntiLHHook/(+, -)AntiRHHook/(+, +)RHStaple conformation due to binding of ligands. Surprisingly, ligands are proximal to the vicinal disulfides in protein complexes that exhibited rare conformations of vicinal disulfides. The report has identified (+, -) LHStaple/(-, -) RHStaple as the hallmark conformations of vicinal disulfides and unraveled ligand-induced transition in conformations of vicinal cysteine disulfides in proteins.
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Affiliation(s)
- K Kasi Amarnath Reddy
- Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, India
| | - Muddagoni Jayashree
- Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, India
| | - Panchada Ch V Govindu
- Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, India
| | - Konkallu Hanumae Gowd
- Department of Chemistry, School of Chemical Sciences, Central University of Karnataka, Kalaburagi, India
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The Cu(II) Reductase RclA Protects Escherichia coli against the Combination of Hypochlorous Acid and Intracellular Copper. mBio 2020; 11:mBio.01905-20. [PMID: 32994322 PMCID: PMC7527725 DOI: 10.1128/mbio.01905-20] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Enterobacteria, including Escherichia coli, bloom to high levels in the gut during inflammation and strongly contribute to the pathology of inflammatory bowel diseases. To survive in the inflamed gut, E. coli must tolerate high levels of antimicrobial compounds produced by the immune system, including toxic metals like copper and reactive chlorine oxidants such as hypochlorous acid (HOCl). Here, we show that extracellular copper is a potent detoxifier of HOCl and that the widely conserved bacterial HOCl resistance enzyme RclA, which catalyzes the reduction of copper(II) to copper(I), specifically protects E. coli against damage caused by the combination of HOCl and intracellular copper. E. coli lacking RclA was highly sensitive to HOCl when grown in the presence of copper and was defective in colonizing an animal host. Our results indicate that there is unexpected complexity in the interactions between antimicrobial toxins produced by innate immune cells and that bacterial copper status is a key determinant of HOCl resistance and suggest an important and previously unsuspected role for copper redox reactions during inflammation.IMPORTANCE During infection and inflammation, the innate immune system uses antimicrobial compounds to control bacterial populations. These include toxic metals, like copper, and reactive oxidants, including hypochlorous acid (HOCl). We have now found that RclA, a copper(II) reductase strongly induced by HOCl in proinflammatory Escherichia coli and found in many bacteria inhabiting epithelial surfaces, is required for bacteria to resist killing by the combination of intracellular copper and HOCl and plays an important role in colonization of an animal host. This finding indicates that copper redox chemistry plays a critical and previously underappreciated role in bacterial interactions with the innate immune system.
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Kerber T, Vrielink A. The role of hydrogen atoms in redox catalysis by the flavoenzyme cholesterol oxidase. Methods Enzymol 2020; 634:361-377. [PMID: 32093840 DOI: 10.1016/bs.mie.2019.12.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
Abstract
Flavoenzymes comprise a large class of proteins that carry out a diverse range of important redox chemistry. Although X-ray crystal structures of many flavoenzymes have been determined, there are still unresolved questions regarding the actual oxidation state of the flavin cofactors in these structures due to photoreduction by the ionizing radiation of the X-ray beam during the diffraction experiment. Additionally, the ability to visualize hydrogen atoms in X-ray structures is difficult due to the weak scattering capability of these atoms. Since hydrogen atoms affect the electrostatic nature of enzyme active sites and play important roles in the chemistry of key amino acid residues, visualizing the precise positions of these atoms provides a more detailed understanding of their role in enzyme catalysis. Single crystal neutron diffraction is an alternative method to structure determination, circumventing problems associated with photoreduction of the sample thus providing a clearer view of the structural features of a flavoenzyme in different redox states. Additionally, the larger neutron scattering factors for hydrogen and deuterium atoms enables one to visualize these atoms much more easily than from X-ray scattering measurements. In this chapter we give an overview of neutron and X-ray crystallography studies on the flavoenzyme, cholesterol oxidase and how the observations of unusual hydrogen atom positions provide insight into the redox chemistry of the flavin cofactor.
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Affiliation(s)
- Tatiana Kerber
- School of Molecular Sciences, University of Western Australia, Perth, WA, Australia
| | - Alice Vrielink
- School of Molecular Sciences, University of Western Australia, Perth, WA, Australia.
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Baek Y, Kim J, Ahn J, Jo I, Hong S, Ryu S, Ha NC. Structure and function of the hypochlorous acid-induced flavoprotein RclA from Escherichia coli. J Biol Chem 2020; 295:3202-3212. [PMID: 31988242 DOI: 10.1074/jbc.ra119.011530] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 01/22/2020] [Indexed: 12/24/2022] Open
Abstract
In response to microbial invasion, the animal immune system generates hypochlorous acid (HOCl) that kills microorganisms in the oxidative burst. HOCl toxicity is amplified in the phagosome through import of the copper cation (Cu2+). In Escherichia coli and Salmonella, the transcriptional regulator RclR senses HOCl stress and induces expression of the RclA, -B, and -C proteins involved in bacterial defenses against oxidative stress. However, the structures and biochemical roles of the Rcl proteins remain to be elucidated. In this study, we first examined the role of the flavoprotein disulfide reductase (FDR) RclA in the survival of Salmonella in macrophage phagosomes, finding that RclA promotes Salmonella survival in macrophage vacuoles containing sublethal HOCl levels. To clarify the molecular mechanism, we determined the crystal structure of RclA from E. coli at 2.9 Å resolution. This analysis revealed that the structure of homodimeric RclA is similar to those of typical FDRs, exhibiting two conserved cysteine residues near the flavin ring of the cofactor flavin adenine dinucleotide (FAD). Of note, we observed that Cu2+ accelerated RclA-mediated oxidation of NADH, leading to a lowering of oxygen levels in vitro Compared with the RclA WT enzyme, substitution of the conserved cysteine residues lowered the specificity to Cu2+ or substantially increased the production of superoxide anion in the absence of Cu2+ We conclude that RclA-mediated lowering of oxygen levels could contribute to the inhibition of oxidative bursts in phagosomes. Our study sheds light on the molecular basis for how bacteria can survive HOCl stress in macrophages.
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Affiliation(s)
- Yeongjin Baek
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Jinwoo Kim
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Jinsook Ahn
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Inseong Jo
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Seokho Hong
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Sangryeol Ryu
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea
| | - Nam-Chul Ha
- Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, and Research Institute for Agriculture and Life Sciences, CALS, Seoul National University, Seoul 08826, Republic of Korea.
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19
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Szekeres LI, Bálint S, Galbács G, Kálomista I, Kiss T, Larsen FH, Hemmingsen L, Jancsó A. Hg 2+ and Cd 2+ binding of a bioinspired hexapeptide with two cysteine units constructed as a minimalistic metal ion sensing fluorescent probe. Dalton Trans 2019; 48:8327-8339. [PMID: 31111849 DOI: 10.1039/c9dt01141b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Hg2+ and Cd2+ complexation of a short hexapeptide, Ac-DCSSCY-NH2 (DY), was studied by pH-potentiometry, UV and NMR spectroscopy and fluorimetry in aqueous solutions and the Hg2+-binding ability of the ligand was also described in an immobilized form, where the peptides were anchored to a hydrophilic resin. Hg2+ was demonstrated to form a 1 : 1 complex with the ligand even at pH = 2.0 while Cd2+ coordination by the peptide takes place only above pH ∼ 3.5. Both metal ions form bis-ligand complexes by the coordination of four Cys-thiolates at ligand excess above pH ∼ 5.5 (Cd2+) and 7.0 (Hg2+). Fluorescence studies demonstrated a Hg2+ induced concentration-dependent quenching of the Tyr fluorescence until a 1 : 1 Hg2+ : DY ratio. The fluorescence emission intensity decreases linearly with the increasing Hg2+ concentration in a range of over two orders of magnitude. The fact that this occurs even in the presence of 1.0 eq. of Cd2+ per ligand reflects a complete displacement of the latter metal ion by Hg2+ from its peptide-bound form. The immobilized peptide was also shown to bind Hg2+ very efficiently even from samples at pH = 2.0. However, the existence of lower affinity binding sites was also demonstrated by binding of more than 1.0 eq. of Hg2+ per immobilized DY molecule under Hg2+-excess conditions. Experiments performed with a mixture of four metal ions, Hg2+, Cd2+, Zn2+ and Ni2+, indicate that this molecular probe may potentially be used in Hg2+-sensing systems under acidic conditions for the measurement of μM range concentrations.
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Affiliation(s)
- Levente I Szekeres
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
| | - Sára Bálint
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
| | - Gábor Galbács
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
| | - Ildikó Kálomista
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
| | - Tamás Kiss
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
| | - Flemming H Larsen
- Department of Food Science, University of Copenhagen, Rolighedsvej 30, 1958 Frederiksberg C, Denmark
| | - Lars Hemmingsen
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - Attila Jancsó
- Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, Szeged, H-6720, Hungary.
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Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool. mBio 2019; 10:mBio.00183-19. [PMID: 30940703 PMCID: PMC6445937 DOI: 10.1128/mbio.00183-19] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Thermus thermophilus is a deep-branching thermophilic aerobe. It is a member of the Deinococcus-Thermus phylum that, together with the Aquificae, constitute the earliest branching aerobic bacterial lineages; therefore, this organism serves as a model for early diverged bacteria (R. K. Hartmann, J. Wolters, B. Kröger, S. Schultze, et al., Syst Appl Microbiol 11:243–249, 1989, https://doi.org/10.1016/S0723-2020(89)80020-7) whose natural heated habitat may contain mercury of geological origins (G. G. Geesey, T. Barkay, and S. King, Sci Total Environ 569-570:321–331, 2016, https://doi.org/10.1016/j.scitotenv.2016.06.080). T. thermophilus likely arose shortly after the oxidation of the biosphere 2.4 billion years ago. Studying T. thermophilus physiology provides clues about the origin and evolution of mechanisms for mercury and oxidative stress responses, the latter being critical for the survival and function of all extant aerobes. Mercury (Hg) is a widely distributed, toxic heavy metal with no known cellular role. Mercury toxicity has been linked to the production of reactive oxygen species (ROS), but Hg does not directly perform redox chemistry with oxygen. How exposure to the ionic form, Hg(II), generates ROS is unknown. Exposure of Thermus thermophilus to Hg(II) triggered ROS accumulation and increased transcription and activity of superoxide dismutase (Sod) and pseudocatalase (Pcat); however, Hg(II) inactivated Sod and Pcat. Strains lacking Sod or Pcat had increased oxidized bacillithiol (BSH) levels and were more sensitive to Hg(II) than the wild type. The ΔbshA Δsod and ΔbshA Δpcat double mutant strains were as sensitive to Hg(II) as the ΔbshA strain that lacks bacillithiol, suggesting that the increased sensitivity to Hg(II) in the Δsod and Δpcat mutant strains is due to a decrease of reduced BSH. Treatment of T. thermophilus with Hg(II) decreased aconitase activity and increased the intracellular concentration of free Fe, and these phenotypes were exacerbated in Δsod and Δpcat mutant strains. Treatment with Hg(II) also increased DNA damage. We conclude that sequestration of the redox buffering thiol BSH by Hg(II), in conjunction with direct inactivation of ROS-scavenging enzymes, impairs the ability of T. thermophilus to effectively metabolize ROS generated as a normal consequence of growth in aerobic environments.
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Ramadan E, Maged M, El Hosseiny A, Chambergo FS, Setubal JC, El Dorry H. Molecular Adaptations of Bacterial Mercuric Reductase to the Hypersaline Kebrit Deep in the Red Sea. Appl Environ Microbiol 2019; 85:e01431-18. [PMID: 30504211 PMCID: PMC6365835 DOI: 10.1128/aem.01431-18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 11/20/2018] [Indexed: 11/20/2022] Open
Abstract
The hypersaline Kebrit Deep brine pool in the Red Sea is characterized by high levels of toxic heavy metals. Here, we describe two structurally related mercuric reductases (MerAs) from this site which were expressed in Escherichia coli Sequence similarities suggest that both genes are derived from proteobacteria, most likely the Betaproteobacteria or Gammaproteobacteria We show that one of the enzymes (K35NH) is strongly inhibited by NaCl, while the other (K09H) is activated in a NaCl-dependent manner. We infer from this difference that the two forms might support the detoxification of mercury in bacterial microorganisms that employ the compatible solutes and salt-in strategies, respectively. Three-dimensional structure modeling shows that all amino acid substitutions unique to each type are located outside the domain responsible for formation of the active MerA homodimer, and the vast majority of these are found on the surface of the molecule. Moreover, K09H exhibits the predominance of acidic over hydrophobic side chains that is typical of halophilic salt-dependent proteins. These findings enhance our understanding of how selection pressures imposed by two environmental stressors have endowed MerA enzymes with catalytic properties that can potentially function in microorganisms that utilize distinct mechanisms for osmotic balance in hypersaline environments.IMPORTANCE Analysis of two structurally homologous but catalytically distinct mercuric reductases from the Kebrit Deep brine in the Red Sea sheds light on the adaptations that enable microorganisms to cope simultaneously with extreme salinity and toxic mercury compounds. One is strongly inhibited by high NaCl concentrations, while the other exhibits NaCl-dependent activation. Their different activity profiles imply that they may derive from bacterial microorganisms that utilize compatible solutes and salt-in strategies, respectively, to maintain osmotic balance. Three-dimensional modeling reveals that regions not involved in formation of the active homodimer are conserved between the two. However, in the NaCl-dependent form, distinct amino acid substitutions are found in areas that are critical for stability in high salt. The work provides insights into how two environmental stressors have shaped the structure of orthologous enzymes through selection and adaptation, enabling them to retain their catalytic function in what may be very different cellular contexts.
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Affiliation(s)
- Eman Ramadan
- Department of Biology, School of Sciences and Engineering, The American University in Cairo, New Cairo, Egypt
| | - Mohamad Maged
- Department of Biology, School of Sciences and Engineering, The American University in Cairo, New Cairo, Egypt
| | - Ahmed El Hosseiny
- Department of Biology, School of Sciences and Engineering, The American University in Cairo, New Cairo, Egypt
| | - Felipe S Chambergo
- Escola de Artes Ciências e Humanidades, Universidade de São Paulo, São Paulo, Brazil
| | - João C Setubal
- Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Hamza El Dorry
- Department of Biology, School of Sciences and Engineering, The American University in Cairo, New Cairo, Egypt
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22
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Thermal Stability of a Mercuric Reductase from the Red Sea Atlantis II Hot Brine Environment as Analyzed by Site-Directed Mutagenesis. Appl Environ Microbiol 2019; 85:AEM.02387-18. [PMID: 30446558 DOI: 10.1128/aem.02387-18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 11/11/2018] [Indexed: 01/28/2023] Open
Abstract
The lower convective layer (LCL) of the Atlantis II brine pool of the Red Sea is a unique environment in terms of high salinity, temperature, and high concentrations of heavy metals. Mercuric reductase enzymes functional in such extreme conditions could be considered a potential tool in the environmental detoxification of mercurial poisoning and might alleviate ecological hazards in the mining industry. Here, we constructed a mercuric reductase library from Atlantis II, from which we identified genes encoding two thermostable mercuric reductase (MerA) isoforms: one is halophilic (designated ATII-LCL) while the other is not (designated ATII-LCL-NH). The ATII-LCL MerA has a short motif composed of four aspartic acids (4D414-417) and two characteristic signature boxes that played a crucial role in its thermal stability. To further understand the mechanism behind the thermostability of the two studied enzymes, we mutated the isoform ATII-LCL-NH and found that the substitution of 2 aspartic acids (2D) at positions 415 and 416 enhanced the thermal stability, while other mutations had the opposite effect. The 2D mutant showed superior thermal tolerance, as it retained 81% of its activity after 10 min of incubation at 70°C. A three-dimensional structure prediction revealed newly formed salt bridges and H bonds in the 2D mutant compared to the parent molecule. To the best of our knowledge, this study is the first to rationally design a mercuric reductase with enhanced thermal stability, which we propose to have a strong potential in the bioremediation of mercurial poisoning.IMPORTANCE The Red Sea is an attractive environment for bioprospecting. There are 25 brine-filled deeps in the Red Sea. The Atlantis II brine pool is the biggest and hottest of such hydrothermal ecosystems. We generated an environmental mercuric reductase library from the lowermost layer of the Atlantis II brine pool, in which we identified two variants of the mercuric reductase enzyme (MerA). One is the previously described halophilic and thermostable ATII-LCL MerA and the other is a nonhalophilic relatively less thermostable enzyme, designated ATII-LCL-NH MerA. We used the ATII-LCL-NH enzyme as a parent molecule to locate the amino acid residues involved in the noticeably higher thermotolerance of the homolog ATII-LCL MerA. Moreover, we designed a novel enzyme with superior thermal stability. This enzyme might have strong potential in the bioremediation of mercuric toxicity.
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23
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Karri R, Chalana A, Das R, Rai RK, Roy G. Cytoprotective effects of imidazole-based [S 1] and [S 2]-donor ligands against mercury toxicity: a bioinorganic approach. Metallomics 2019; 11:213-225. [PMID: 30488926 DOI: 10.1039/c8mt00237a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Here we report the coordination behaviour of an imidazole-based [S1]-donor ligand, 1,3-dimethyl-imidazole-2(3H)-thione (L1), and [S2]-donor ligand, 3,3'-methylenebis(1-methyl-imidazole-2(3H)-thione) (L2) or 4,4'-(3,3'-methylenebis-(2-thioxo-2,3-dihydro-imidazole-3,1-diyl))dibutanoic acid (L3), with HgX2 (X = Cl, Br or I) in solution and the solid state. NMR, UV-Vis spectroscopic, and single crystal X-ray studies demonstrated that L1 or L2 coordinated rapidly and reversibly to the mercury center of HgX2 through the thione moiety. Treatment of L2 with HgCl2 or HgBr2 afforded 16-membered metallacycle k1-(L2)2Hg2Cl4 or k1-(L2)2Hg2Br4 where two Cl or Br atoms are located inside the ring. In contrast, treatment of L2 with HgI2 afforded a chain-like structure of k1-[L2Hgl2]n, possibly due to the large size of the iodine atom. Interestingly, [S1] and [S2]-donor ligands (L1, L2, and L3) showed an excellent efficacy to protect liver cells against HgCl2 induced toxicity and the strength of their efficacy is in the order of L3 > L2 > L1. 30% decrease of ROS production was observed when liver cells were co-treated with HgCl2 and L1 in comparison to those cells treated with HgCl2 only. In contrast, 45% and 60% decrease of ROS production was observed in the case of cells co-treated with HgCl2 and thiones L2 and L3, respectively, indicating that [S2]-donor ligands L2 and L3 have better cytoprotective effects against oxidative stress induced by HgCl2 than [S1]-donor ligand L1. Water-soluble ligand L3 with N-(CH2)3CO2H substituents showed a better cytoprotective effect against HgCl2 toxicity than L2 in liver cells.
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Affiliation(s)
- Ramesh Karri
- Department of Chemistry, School of Natural Sciences, Shiv Nadar University, NH91, Dadri, Gautam Buddha Nagar, UP 201314, India.
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Kilgore HR, Raines RT. n→π* Interactions Modulate the Properties of Cysteine Residues and Disulfide Bonds in Proteins. J Am Chem Soc 2018; 140:17606-17611. [PMID: 30403347 DOI: 10.1021/jacs.8b09701] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Noncovalent interactions are ubiquitous in biology, taking on roles that include stabilizing the conformation of and assembling biomolecules, and providing an optimal environment for enzymatic catalysis. Here, we describe a noncovalent interaction that engages the sulfur atoms of cysteine residues and disulfide bonds in proteins-their donation of electron density into an antibonding orbital of proximal amide carbonyl groups. This n→ π* interaction tunes the reactivity of the CXXC motif, which is the critical feature of thioredoxin and other enzymes involved in redox homeostasis. In particular, an n→ π* interaction lowers the p Ka value of the N-terminal cysteine residue of the motif, which is the nucleophile that initiates catalysis. In addition, the interplay between disulfide n→ π* interactions and C5 hydrogen bonds leads to hyperstable β-strands. Finally, n→ π* interactions stabilize vicinal disulfide bonds, which are naturally diverse in function. These previously unappreciated n→ π* interactions are strong and underlie the ability of cysteine residues and disulfide bonds to engage in the structure and function of proteins.
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Affiliation(s)
- Henry R Kilgore
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Ronald T Raines
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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Chen CT, Liao YY, Salunke SB, Lin YH, Kuo TS. Directed Self-Assembly of C 4-Symmetric, Oxidovanadate-Centered, Vanadyl(V) Quadruplexes for Ba 2+- and Hg 2+-Specific Recognition, Transport, and Recovery. Inorg Chem 2018; 57:11511-11523. [PMID: 30183263 DOI: 10.1021/acs.inorgchem.8b01454] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Directed assembly of loosely, Na+-bound, oxidovanadate-centered quartets of C4-symmetry from tailor-made chiral N-salicylidene-vanadyl(V) complexes, for the first time, allows for highly efficient Ba2+- or Hg2+-specific detection (by 51V NMR and VCD), transport (forming a unique helical capsule or a capped square planar complex, respectively), and green recovery from an aqueous phase containing 4 different alkaline earth ions or from at least 10 different metal ions of similar size and charge capacity into the CHCl3 layer without interference from oxa- or oxophilic ions like Mg2+, Ca2+, Cu2+, Cd2+, and Pb2+.
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Affiliation(s)
- Chien-Tien Chen
- Department of Chemistry , National Tsing Hua University , Hsinchu , Taiwan
| | - Yi-Ya Liao
- Department of Chemistry , National Tsing Hua University , Hsinchu , Taiwan
| | | | - Ya-Hui Lin
- National Taiwan Normal University , Taipei , Taiwan
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Low-Molecular-Weight Thiols and Thioredoxins Are Important Players in Hg(II) Resistance in Thermus thermophilus HB27. Appl Environ Microbiol 2018; 84:AEM.01931-17. [PMID: 29150497 DOI: 10.1128/aem.01931-17] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 10/24/2017] [Indexed: 12/31/2022] Open
Abstract
Mercury (Hg), one of the most toxic and widely distributed heavy metals, has a high affinity for thiol groups. Thiol groups reduce and sequester Hg. Therefore, low-molecular-weight (LMW) and protein thiols may be important cell components used in Hg resistance. To date, the role of low-molecular-weight thiols in Hg detoxification remains understudied. The mercury resistance (mer) operon of Thermus thermophilus suggests an evolutionary link between Hg(II) resistance and low-molecular-weight thiol metabolism. The mer operon encodes an enzyme involved in methionine biosynthesis, Oah. Challenge with Hg(II) resulted in increased expression of genes involved in the biosynthesis of multiple low-molecular-weight thiols (cysteine, homocysteine, and bacillithiol), as well as the thioredoxin system. Phenotypic analysis of gene replacement mutants indicated that Oah contributes to Hg resistance under sulfur-limiting conditions, and strains lacking bacillithiol and/or thioredoxins are more sensitive to Hg(II) than the wild type. Growth in the presence of either a thiol-oxidizing agent or a thiol-alkylating agent increased sensitivity to Hg(II). Furthermore, exposure to 3 μM Hg(II) consumed all intracellular reduced bacillithiol and cysteine. Database searches indicate that oah2 is present in all Thermus sp. mer operons. The presence of a thiol-related gene was also detected in some alphaproteobacterial mer operons, in which a glutathione reductase gene was present, supporting the role of thiols in Hg(II) detoxification. These results have led to a working model in which LMW thiols act as Hg(II)-buffering agents while Hg is reduced by MerA.IMPORTANCE The survival of microorganisms in the presence of toxic metals is central to life's sustainability. The affinity of thiol groups for toxic heavy metals drives microbe-metal interactions and modulates metal toxicity. Mercury detoxification (mer) genes likely originated early in microbial evolution in geothermal environments. Little is known about how mer systems interact with cellular thiol systems. Thermus spp. possess a simple mer operon in which a low-molecular-weight thiol biosynthesis gene is present, along with merR and merA In this study, we present experimental evidence for the role of thiol systems in mercury resistance. Our data suggest that, in T. thermophilus, thiolated compounds may function side by side with mer genes to detoxify mercury. Thus, thiol systems function in consort with mer-mediated resistance to mercury, suggesting exciting new questions for future research.
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Mesterházy E, Lebrun C, Crouzy S, Jancsó A, Delangle P. Short oligopeptides with three cysteine residues as models of sulphur-rich Cu(i)- and Hg(ii)-binding sites in proteins. Metallomics 2018; 10:1232-1244. [DOI: 10.1039/c8mt00113h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Peptides mimicking sulphur-rich fragments found in metallothioneins display unexpectedly different behaviours with the two metal ions Hg(ii) and Cu(i).
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Affiliation(s)
- Edit Mesterházy
- INAC/SYMMES/Université Grenoble Alpes
- CEA
- CNRS
- 38000 Grenoble
- France
| | - Colette Lebrun
- Department of Inorganic and Analytical Chemistry
- University of Szeged
- Szeged H-6720
- Hungary
| | - Serge Crouzy
- BIG/LCBM/Université Grenoble Alpes
- CEA
- CNRS
- (UMR 5249)
- 38000 Grenoble
| | - Attila Jancsó
- Department of Inorganic and Analytical Chemistry
- University of Szeged
- Szeged H-6720
- Hungary
| | - Pascale Delangle
- INAC/SYMMES/Université Grenoble Alpes
- CEA
- CNRS
- 38000 Grenoble
- France
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28
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Dash HR, Sahu M, Mallick B, Das S. Functional efficiency of MerA protein among diverse mercury resistant bacteria for efficient use in bioremediation of inorganic mercury. Biochimie 2017; 142:207-215. [DOI: 10.1016/j.biochi.2017.09.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 09/26/2017] [Indexed: 10/18/2022]
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29
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Keirsse-Haquin J, Picaud T, Bordes L, de Gracia AG, Desbois A. Modulation of the flavin-protein interactions in NADH peroxidase and mercuric ion reductase: a resonance Raman study. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2017; 47:205-223. [PMID: 28889232 DOI: 10.1007/s00249-017-1245-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/12/2017] [Accepted: 07/26/2017] [Indexed: 10/18/2022]
Abstract
NADH peroxidase (Npx) and mercuric ion reductase (MerA) are flavoproteins belonging to the pyridine nucleotide:disulfide oxidoreductases (PNDO) and catalyzing the reduction of toxic substrates, i.e., hydrogen peroxide and mercuric ion, respectively. To determine the role of the flavin adenine dinucleotide (FAD) in the detoxification mechanism, the resonance Raman (RR) spectra of these enzymes under various redox and ligation states have been investigated using blue and/or near-UV excitation(s). These data were compared to those previously obtained for glutathione reductase (GR), another enzyme of the PNDO family, but catalyzing the reduction of oxidized glutathione. Spectral differences have been detected for the marker bands of the isoalloxazine ring of Npx, MerA, and GR. They provide evidence for different catalytic mechanisms in these flavoproteins. The RR modes of the oxidized and two-electron reduced (EH2) forms of Npx are related to very tight flavin-protein interactions maintaining a nearly planar conformation of the isoalloxazine tricycle, a low level of H-bonding at the N1/N5 and O2/O4 sites, and a strong H-bond at N3H. They also indicate minimal changes in FAD structure and environment upon either NAD(H) binding or reduction of the sulfinic redox center. All these spectroscopic data support an enzyme functioning centered on the Cys-SO-/Cys-S- redox moiety and a neighbouring His residue. On the contrary, the RR data on various functional forms of MerA are indicative of a modulation of both ring II distortion and H-bonding states of the N5 site and ring III. The Cd(II) binding to the EH2-NADP(H) complexes, biomimetic intermediates in the reaction of Hg(II) reduction, provokes important spectral changes. They are interpreted in terms of flattening of the isoalloxazine ring and large decreases in H-bonding at the N5 site and ring III. The large flexibility of the FAD structure and environment in MerA is in agreement with proposed mechanisms involving C4a(flavin) adducts.
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Affiliation(s)
- Julie Keirsse-Haquin
- Institut de Biologie Intégrative de la Cellule, UMR 9198 CNRS-CEA-Université Paris Sud, CEA Saclay, 91191, Gif-sur-Yvette Cedex, France.,Ecole Nationale Supérieure des Mines, 44300, Nantes, France
| | - Thierry Picaud
- Institut de Biologie Intégrative de la Cellule, UMR 9198 CNRS-CEA-Université Paris Sud, CEA Saclay, 91191, Gif-sur-Yvette Cedex, France.,Institut Supérieur des Biotechnologies de Paris (Sup'Biotech Paris), 94800, Villejuif, France
| | - Luc Bordes
- Institut de Biologie Intégrative de la Cellule, UMR 9198 CNRS-CEA-Université Paris Sud, CEA Saclay, 91191, Gif-sur-Yvette Cedex, France.,School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Adrienne Gomez de Gracia
- Institut de Biologie Intégrative de la Cellule, UMR 9198 CNRS-CEA-Université Paris Sud, CEA Saclay, 91191, Gif-sur-Yvette Cedex, France
| | - Alain Desbois
- Institut de Biologie Intégrative de la Cellule, UMR 9198 CNRS-CEA-Université Paris Sud, CEA Saclay, 91191, Gif-sur-Yvette Cedex, France.
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30
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Bafana A, Khan F, Suguna K. Structural and functional characterization of mercuric reductase from Lysinibacillus sphaericus strain G1. Biometals 2017; 30:809-819. [PMID: 28894951 DOI: 10.1007/s10534-017-0050-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 09/04/2017] [Indexed: 11/25/2022]
Abstract
In response to the widespread presence of inorganic Hg in the environment, bacteria have evolved resistance systems with mercuric reductase (MerA) as the key enzyme. MerA enzymes have still not been well characterized from gram positive bacteria. Current study reports physico-chemical, kinetic and structural characterization of MerA from a multiple heavy metal resistant strain of Lysinibacillus sphaericus, and discusses its implications in bioremediation application. The enzyme was homodimeric with subunit molecular weight of about 60 kDa. The Km and Vmax were found to be 32 µM of HgCl2 and 18 units/mg respectively. The enzyme activity was enhanced by β-mercaptoethanol and NaCl up to concentrations of 500 µM and 100 mM respectively, followed by inhibition at higher concentrations. The enzyme showed maximum activity in the pH range of 7-7.5 and temperature range of 25-50 °C, with melting temperature of 67 °C. Cu2+ exhibited pronounced inhibition of the enzyme with mixed inhibition pattern. The enzyme contained FAD as the prosthetic group and used NADPH as the preferred electron donor, but it showed slight activity with NADH as well. Structural characterization was carried out by circular dichroism spectrophotometry and X-ray crystallography. X-ray confirmed the homodimeric structure of enzyme and gave an insight on the residues involved in catalytic binding. In conclusion, the investigated enzyme showed higher catalytic efficiency, temperature stability and salt tolerance as compared to MerA enzymes from other mesophiles. Therefore, it is proposed to be a promising candidate for Hg2+ bioremediation.
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Affiliation(s)
- Amit Bafana
- Environmental Impact and Sustainability Division, CSIR-NEERI (National Environmental Engineering Research Institute), Nagpur, 440020, India.
| | - Farha Khan
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India
| | - Kaza Suguna
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India
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31
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Richardson JS, Videau LL, Williams CJ, Richardson DC. Broad Analysis of Vicinal Disulfides: Occurrences, Conformations with Cis or with Trans Peptides, and Functional Roles Including Sugar Binding. J Mol Biol 2017; 429:1321-1335. [PMID: 28336403 DOI: 10.1016/j.jmb.2017.03.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 10/19/2022]
Abstract
Vicinal disulfides between sequence-adjacent cysteine residues are very rare and rather startling structural features which play a variety of functional roles. Typically discussed as an isolated curiosity, they have never received a general treatment covering both cis and trans forms. Enabled by the growing database of high-resolution structures, required deposition of diffraction data, and improved methods for discriminating reliable from dubious cases, we identify and describe distinct protein families with reliably genuine examples of cis or trans vicinal disulfides and discuss their conformations, conservation, and functions. No cis-trans interconversions and only one case of catalytic redox function are seen. Some vicinal disulfides are essential to large, functionally coupled motions, whereas most form the centers of tightly packed internal regions. Their most widespread biological role is providing a rigid hydrophobic contact surface under the undecorated side of a sugar or multiring ligand, contributing an important aspect of binding specificity.
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Affiliation(s)
- Jane S Richardson
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA.
| | - Lizbeth L Videau
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA
| | | | - David C Richardson
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA
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32
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Arenas-Salinas M, Vargas-Pérez JI, Morales W, Pinto C, Muñoz-Díaz P, Cornejo FA, Pugin B, Sandoval JM, Díaz-Vásquez WA, Muñoz-Villagrán C, Rodríguez-Rojas F, Morales EH, Vásquez CC, Arenas FA. Flavoprotein-Mediated Tellurite Reduction: Structural Basis and Applications to the Synthesis of Tellurium-Containing Nanostructures. Front Microbiol 2016; 7:1160. [PMID: 27507969 PMCID: PMC4960239 DOI: 10.3389/fmicb.2016.01160] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 07/12/2016] [Indexed: 01/24/2023] Open
Abstract
The tellurium oxyanion tellurite (TeO32-) is extremely harmful for most organisms. It has been suggested that a potential bacterial tellurite resistance mechanism would consist of an enzymatic, NAD(P)H-dependent, reduction to the less toxic form elemental tellurium (Te0). To date, a number of enzymes such as catalase, type II NADH dehydrogenase and terminal oxidases from the electron transport chain, nitrate reductases, and dihydrolipoamide dehydrogenase (E3), among others, have been shown to display tellurite-reducing activity. This activity is generically referred to as tellurite reductase (TR). Bioinformatic data resting on some of the abovementioned enzymes enabled the identification of common structures involved in tellurite reduction including vicinal catalytic cysteine residues and the FAD/NAD(P)+-binding domain, which is characteristic of some flavoproteins. Along this line, thioredoxin reductase (TrxB), alkyl hydroperoxide reductase (AhpF), glutathione reductase (GorA), mercuric reductase (MerA), NADH: flavorubredoxin reductase (NorW), dihydrolipoamide dehydrogenase, and the putative oxidoreductase YkgC from Escherichia coli or environmental bacteria were purified and assessed for TR activity. All of them displayed in vitro TR activity at the expense of NADH or NADPH oxidation. In general, optimal reducing conditions occurred around pH 9–10 and 37°C. Enzymes exhibiting strong TR activity produced Te-containing nanostructures (TeNS). While GorA and AhpF generated TeNS of 75 nm average diameter, E3 and YkgC produced larger structures (>100 nm). Electron-dense structures were observed in cells over-expressing genes encoding TrxB, GorA, and YkgC.
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Affiliation(s)
| | - Joaquín I Vargas-Pérez
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Wladimir Morales
- Centro de Bioinformática y Simulación Molecular, Universidad de Talca Talca, Chile
| | - Camilo Pinto
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Pablo Muñoz-Díaz
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Fabián A Cornejo
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Benoit Pugin
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Juan M Sandoval
- Facultad de Ciencias de la Salud e Instituto de Etnofarmacología, Universidad Arturo Prat Iquique, Chile
| | - Waldo A Díaz-Vásquez
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de ChileSantiago, Chile; Facultad de Ciencias de la Salud, Universidad San SebastiánSantiago, Chile
| | - Claudia Muñoz-Villagrán
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Fernanda Rodríguez-Rojas
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Eduardo H Morales
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Claudio C Vásquez
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
| | - Felipe A Arenas
- Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile Santiago, Chile
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LaVoie SP, Mapolelo DT, Cowart DM, Polacco BJ, Johnson MK, Scott RA, Miller SM, Summers AO. Organic and inorganic mercurials have distinct effects on cellular thiols, metal homeostasis, and Fe-binding proteins in Escherichia coli. J Biol Inorg Chem 2015; 20:1239-51. [PMID: 26498643 PMCID: PMC4749482 DOI: 10.1007/s00775-015-1303-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 10/08/2015] [Indexed: 02/07/2023]
Abstract
The protean chemical properties of the toxic metal mercury (Hg) have made it attractive in diverse applications since antiquity. However, growing public concern has led to an international agreement to decrease its impact on health and the environment. During a recent proteomics study of acute Hg exposure in E. coli, we also examined the effects of inorganic and organic Hg compounds on thiol and metal homeostases. On brief exposure, lower concentrations of divalent inorganic mercury Hg(II) blocked bulk cellular thiols and protein-associated thiols more completely than higher concentrations of monovalent organomercurials, phenylmercuric acetate (PMA) and merthiolate (MT). Cells bound Hg(II) and PMA in excess of their available thiol ligands; X-ray absorption spectroscopy indicated nitrogens as likely additional ligands. The mercurials released protein-bound iron (Fe) more effectively than common organic oxidants and all disturbed the Na(+)/K(+) electrolyte balance, but none provoked efflux of six essential transition metals including Fe. PMA and MT made stable cysteine monothiol adducts in many Fe-binding proteins, but stable Hg(II) adducts were only seen in CysXxx(n)Cys peptides. We conclude that on acute exposure: (a) the distinct effects of mercurials on thiol and Fe homeostases reflected their different uptake and valences; (b) their similar effects on essential metal and electrolyte homeostases reflected the energy dependence of these processes; and (c) peptide phenylmercury-adducts were more stable or detectable in mass spectrometry than Hg(II)-adducts. These first in vivo observations in a well-defined model organism reveal differences upon acute exposure to inorganic and organic mercurials that may underlie their distinct toxicology.
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Affiliation(s)
- Stephen P LaVoie
- Department of Microbiology, University of Georgia, Athens, GA, 30602, USA
| | - Daphne T Mapolelo
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA
- Department of Chemistry, University of Botswana, P.O. Box 00704, Gaborone, Botswana
| | - Darin M Cowart
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA
| | - Benjamin J Polacco
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, 94158, USA
| | - Michael K Johnson
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA
| | - Robert A Scott
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA
| | - Susan M Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, 94158, USA
| | - Anne O Summers
- Department of Microbiology, University of Georgia, Athens, GA, 30602, USA.
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Mercury Reduction and Methyl Mercury Degradation by the Soil Bacterium Xanthobacter autotrophicus Py2. Appl Environ Microbiol 2015; 81:7833-8. [PMID: 26341208 DOI: 10.1128/aem.01982-15] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 08/30/2015] [Indexed: 11/20/2022] Open
Abstract
Two previously uncharacterized potential broad-spectrum mercury (Hg) resistance operons (mer) are present on the chromosome of the soil Alphaproteobacteria Xanthobacter autotrophicus Py2. These operons, mer1 and mer2, contain two features which are commonly found in mer operons in the genomes of soil and marine Alphaproteobacteria, but are not present in previously characterized mer operons: a gene for the mercuric reductase (MerA) that encodes an alkylmercury lyase domain typical of those found on the MerB protein, and the presence of an additional gene, which we are calling merK, with homology to glutathione reductase. Here, we demonstrate that Py2 is resistant to 0.2 μM inorganic mercury [Hg(II)] and 0.05 μM methylmercury (MeHg). Py2 is capable of converting MeHg and Hg(II) to elemental mercury [Hg(0)], and reduction of Hg(II) is induced by incubation in sub toxic concentrations of Hg(II). Transcription of the merA genes increased with Hg(II) treatment, and in both operons merK resides on the same polycistronic mRNA as merA. We propose the use of Py2 as a model system for studying the contribution of mer to Hg mobility in soil and marine ecosystems.
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35
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Hong L, Sharp MA, Poblete S, Biehl R, Zamponi M, Szekely N, Appavou MS, Winkler RG, Nauss RE, Johs A, Parks JM, Yi Z, Cheng X, Liang L, Ohl M, Miller SM, Richter D, Gompper G, Smith JC. Structure and dynamics of a compact state of a multidomain protein, the mercuric ion reductase. Biophys J 2015; 107:393-400. [PMID: 25028881 DOI: 10.1016/j.bpj.2014.06.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 05/30/2014] [Accepted: 06/10/2014] [Indexed: 12/11/2022] Open
Abstract
The functional efficacy of colocalized, linked protein domains is dependent on linker flexibility and system compaction. However, the detailed characterization of these properties in aqueous solution presents an enduring challenge. Here, we employ a novel, to our knowledge, combination of complementary techniques, including small-angle neutron scattering, neutron spin-echo spectroscopy, and all-atom molecular dynamics and coarse-grained simulation, to identify and characterize in detail the structure and dynamics of a compact form of mercuric ion reductase (MerA), an enzyme central to bacterial mercury resistance. MerA possesses metallochaperone-like N-terminal domains (NmerA) tethered to its catalytic core domain by linkers. The NmerA domains are found to interact principally through electrostatic interactions with the core, leashed by the linkers so as to subdiffuse on the surface over an area close to the core C-terminal Hg(II)-binding cysteines. How this compact, dynamical arrangement may facilitate delivery of Hg(II) from NmerA to the core domain is discussed.
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Affiliation(s)
- Liang Hong
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Tennessee; Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee; Department of Physics and Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai, China
| | - Melissa A Sharp
- European Spallation Source ESS AB, Lund, Sweden; Jülich Center of Neutron Science, Outstation at the Spallation Neutron Source (SNS), Oak Ridge, Tennessee
| | - Simón Poblete
- Institute of Complex Systems & Institute for Advanced Simulation, Forschungszentrum Jülich, Jülich, Germany
| | - Ralf Biehl
- Jülich Center of Neutron Science & Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany
| | - Michaela Zamponi
- Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH Outstation at MLZ, Garching, Germany
| | - Noemi Szekely
- Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH Outstation at MLZ, Garching, Germany
| | - Marie-Sousai Appavou
- Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH Outstation at MLZ, Garching, Germany
| | - Roland G Winkler
- Institute of Complex Systems & Institute for Advanced Simulation, Forschungszentrum Jülich, Jülich, Germany
| | - Rachel E Nauss
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California
| | - Alexander Johs
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Jerry M Parks
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Tennessee
| | - Zheng Yi
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Tennessee; Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Xiaolin Cheng
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Tennessee
| | - Liyuan Liang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Michael Ohl
- Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH Outstation at MLZ, Garching, Germany.
| | - Susan M Miller
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California.
| | - Dieter Richter
- Jülich Center of Neutron Science & Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany.
| | - Gerhard Gompper
- Institute of Complex Systems & Institute for Advanced Simulation, Forschungszentrum Jülich, Jülich, Germany.
| | - Jeremy C Smith
- Center for Molecular Biophysics, Oak Ridge National Laboratory, Tennessee; Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee.
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36
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Silva PJ, Rodrigues V. Mechanistic pathways of mercury removal from the organomercurial lyase active site. PeerJ 2015; 3:e1127. [PMID: 26246970 PMCID: PMC4525700 DOI: 10.7717/peerj.1127] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 07/03/2015] [Indexed: 11/20/2022] Open
Abstract
Bacterial populations present in Hg-rich environments have evolved biological mechanisms to detoxify methylmercury and other organometallic mercury compounds. The most common resistance mechanism relies on the H+-assisted cleavage of the Hg–C bond of methylmercury by the organomercurial lyase MerB. Although the initial reaction steps which lead to the loss of methane from methylmercury have already been studied experimentally and computationally, the reaction steps leading to the removal of Hg2+ from MerB and regeneration of the active site for a new round of catalysis have not yet been elucidated. In this paper, we have studied the final steps of the reaction catalyzed by MerB through quantum chemical computations at the combined MP2/CBS//B3PW91/6-31G(d) level of theory. While conceptually simple, these reaction steps occur in a complex potential energy surface where several distinct pathways are accessible and may operate concurrently. The only pathway which clearly emerges as forbidden in our analysis is the one arising from the sequential addition of two thiolates to the metal atom, due to the accumulation of negative charges in the active site. The addition of two thiols, in contrast, leads to two feasible mechanistic possibilities. The most straightforward pathway proceeds through proton transfer from the attacking thiol to Cys159 , leading to its removal from the mercury coordination sphere, followed by a slower attack of a second thiol, which removes Cys96. The other pathway involves Asp99 in an accessory role similar to the one observed earlier for the initial stages of the reaction and affords a lower activation enthalpy, around 14 kcal mol−1, determined solely by the cysteine removal step rather than by the thiol ligation step. Addition of one thiolate to the intermediates arising from either thiol attack occurs without a barrier and produces an intermediate bound to one active site cysteine and from which Hg(SCH3)2 may be removed only after protonation by solvent-provided H3O+. Thiolate addition to the active site (prior to any attack by thiols) leads to pathways where the removal of the first cysteine becomes the rate-determining step, irrespective of whether Cys159 or Cys96 leaves first. Comparisons with the recently computed mechanism of the related enzyme MerA further underline the important role of Asp99 in the energetics of the MerB reaction. Kinetic simulation of the mechanism derived from our computations strongly suggests that in vivo the thiolate-only pathway is operative, and the Asp-assisted pathway (as well as the conversion of intermediates of the thiolate pathway into intermediates of the Cys-assisted pathway) is prevented by steric factors absent from our model and related to the precise geometry of the organomercurial binding-pocket.
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Affiliation(s)
- Pedro J Silva
- FP-ENAS/Fac. de Ciências da Saúde, Universidade Fernando Pessoa , Porto , Portugal
| | - Viviana Rodrigues
- FP-ENAS/Fac. de Ciências da Saúde, Universidade Fernando Pessoa , Porto , Portugal
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37
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Artz JH, White SN, Zadvornyy OA, Fugate CJ, Hicks D, Gauss GH, Posewitz MC, Boyd ES, Peters JW. Biochemical and Structural Properties of a Thermostable Mercuric Ion Reductase from Metallosphaera sedula. Front Bioeng Biotechnol 2015. [PMID: 26217660 PMCID: PMC4500099 DOI: 10.3389/fbioe.2015.00097] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Mercuric ion reductase (MerA), a mercury detoxification enzyme, has been tuned by evolution to have high specificity for mercuric ions (Hg2+) and to catalyze their reduction to a more volatile, less toxic elemental form. Here, we present a biochemical and structural characterization of MerA from the thermophilic crenarchaeon Metallosphaera sedula. MerA from M. sedula is a thermostable enzyme, and remains active after extended incubation at 97°C. At 37°C, the NADPH oxidation-linked Hg2+ reduction specific activity was found to be 1.9 μmol/min⋅mg, increasing to 3.1 μmol/min⋅mg at 70°C. M. sedula MerA crystals were obtained and the structure was solved to 1.6 Å, representing the first solved crystal structure of a thermophilic MerA. Comparison of both the crystal structure and amino acid sequence of MerA from M. sedula to mesophillic counterparts provides new insights into the structural determinants that underpin the thermal stability of the enzyme.
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Affiliation(s)
- Jacob H Artz
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - Spencer N White
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - Oleg A Zadvornyy
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - Corey J Fugate
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - Danny Hicks
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - George H Gauss
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
| | - Matthew C Posewitz
- Department of Chemistry and Geochemistry, Colorado School of Mines , Golden, CO , USA
| | - Eric S Boyd
- Department of Microbiology and Immunology, Montana State University , Bozeman, MT , USA ; Thermal Biology Institute, Montana State University , Bozeman, MT , USA
| | - John W Peters
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, MT , USA
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38
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Rubino FM. Toxicity of Glutathione-Binding Metals: A Review of Targets and Mechanisms. TOXICS 2015; 3:20-62. [PMID: 29056650 PMCID: PMC5634692 DOI: 10.3390/toxics3010020] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 09/04/2014] [Accepted: 01/14/2015] [Indexed: 02/07/2023]
Abstract
Mercury, cadmium, arsenic and lead are among priority metals for toxicological studies due to the frequent human exposure and to the significant burden of disease following acute and chronic intoxication. Among their common characteristics is chemical affinity to proteins and non-protein thiols and their ability to generate cellular oxidative stress by the best-known Fenton mechanism. Their health effects are however diverse: kidney and liver damage, cancer at specific sites, irreversible neurological damages with metal-specific features. Mechanisms for the induction of oxidative stress by interaction with the cell thiolome will be presented, based on literature evidence and of experimental findings.
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Affiliation(s)
- Federico Maria Rubino
- LaTMA Laboratory for Analytical Toxicology and Metabonomics, Department of Health Sciences, Università degli Studi di Milano at "Ospedale San Paolo" v. A. di Rudinì 8, I-20142 Milano, Italy.
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39
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Lian P, Guo HB, Riccardi D, Dong A, Parks JM, Xu Q, Pai EF, Miller SM, Wei DQ, Smith JC, Guo H. X-ray structure of a Hg2+ complex of mercuric reductase (MerA) and quantum mechanical/molecular mechanical study of Hg2+ transfer between the C-terminal and buried catalytic site cysteine pairs. Biochemistry 2014; 53:7211-22. [PMID: 25343681 PMCID: PMC4245977 DOI: 10.1021/bi500608u] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
![]()
Mercuric reductase, MerA, is a key
enzyme in bacterial mercury
resistance. This homodimeric enzyme captures and reduces toxic Hg2+ to Hg0, which is relatively unreactive and can
exit the cell passively. Prior to reduction, the Hg2+ is
transferred from a pair of cysteines (C558′ and C559′
using Tn501 numbering) at the C-terminus of one monomer
to another pair of cysteines (C136 and C141) in the catalytic site
of the other monomer. Here, we present the X-ray structure of the
C-terminal Hg2+ complex of the C136A/C141A double mutant
of the Tn501 MerA catalytic core and explore the
molecular mechanism of this Hg transfer with quantum mechanical/molecular
mechanical (QM/MM) calculations. The transfer is found to be nearly
thermoneutral and to pass through a stable tricoordinated intermediate
that is marginally less stable than the two end states. For the overall
process, Hg2+ is always paired with at least two thiolates
and thus is present at both the C-terminal and catalytic binding sites
as a neutral complex. Prior to Hg2+ transfer, C141 is negatively
charged. As Hg2+ is transferred into the catalytic site,
a proton is transferred from C136 to C559′ while C558′
becomes negatively charged, resulting in the net transfer of a negative
charge over a distance of ∼7.5 Å. Thus, the transport
of this soft divalent cation is made energetically feasible by pairing
a competition between multiple Cys thiols and/or thiolates for Hg2+ with a competition between the Hg2+ and protons
for the thiolates.
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Affiliation(s)
- Peng Lian
- The State Key Laboratory of Microbial Metabolism and College of Life Sciences and Biotechnology, Shanghai Jiao Tong University , Shanghai 200240, China
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40
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Sayed A, Ghazy MA, Ferreira AJS, Setubal JC, Chambergo FS, Ouf A, Adel M, Dawe AS, Archer JAC, Bajic VB, Siam R, El-Dorry H. A novel mercuric reductase from the unique deep brine environment of Atlantis II in the Red Sea. J Biol Chem 2013; 289:1675-87. [PMID: 24280218 DOI: 10.1074/jbc.m113.493429] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A unique combination of physicochemical conditions prevails in the lower convective layer (LCL) of the brine pool at Atlantis II (ATII) Deep in the Red Sea. With a maximum depth of over 2000 m, the pool is characterized by acidic pH (5.3), high temperature (68 °C), salinity (26%), low light levels, anoxia, and high concentrations of heavy metals. We have established a metagenomic dataset derived from the microbial community in the LCL, and here we describe a gene for a novel mercuric reductase, a key component of the bacterial detoxification system for mercuric and organomercurial species. The metagenome-derived gene and an ortholog from an uncultured soil bacterium were synthesized and expressed in Escherichia coli. The properties of their products show that, in contrast to the soil enzyme, the ATII-LCL mercuric reductase is functional in high salt, stable at high temperatures, resistant to high concentrations of Hg(2+), and efficiently detoxifies Hg(2+) in vivo. Interestingly, despite the marked functional differences between the orthologs, their amino acid sequences differ by less than 10%. Site-directed mutagenesis and kinetic analysis of the mutant enzymes, in conjunction with three-dimensional modeling, have identified distinct structural features that contribute to extreme halophilicity, thermostability, and high detoxification capacity, suggesting that these were acquired independently during the evolution of this enzyme. Thus, our work provides fundamental structural insights into a novel protein that has undergone multiple biochemical and biophysical adaptations to promote the survival of microorganisms that reside in the extremely demanding environment of the ATII-LCL.
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Affiliation(s)
- Ahmed Sayed
- From the Department of Biology and the Science and Technology Research Center, School of Sciences and Engineering, The American University in Cairo, AUC Avenue, P. O. Box 74, New Cairo 11835, Egypt
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41
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Schelert J, Rudrappa D, Johnson T, Blum P. Role of MerH in mercury resistance in the archaeon Sulfolobus solfataricus. MICROBIOLOGY-SGM 2013; 159:1198-1208. [PMID: 23619003 DOI: 10.1099/mic.0.065854-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Crenarchaeota include extremely thermoacidophilic organisms that thrive in geothermal environments dominated by sulfidic ores and heavy metals such as mercury. Mercuric ion, Hg(II), inactivates transcription in the crenarchaeote Sulfolobus solfataricus and simultaneously derepresses transcription of a resistance operon, merHAI, through interaction with the MerR transcription factor. While mercuric reductase (MerA) is required for metal resistance, the role of MerH, an adjacent small and predicted product of an ORF, has not been explored. Inactivation of MerH either by nonsense mutation or by in-frame deletion diminished Hg(II) resistance of mutant cells. Promoter mapping studies indicated that Hg(II) sensitivity of the merH nonsense mutant arose through transcriptional polarity, and its metal resistance was restored partially by single copy merH complementation. Since MerH was not required in vitro for MerA-catalysed Hg(II) reduction, MerH may play an alternative role in metal resistance. Inductively coupled plasma-mass spectrometry analysis of the MerH deletion strain following metal challenge indicated that there was prolonged retention of intracellular Hg(II). Finally, a reduced rate of mer operon induction in the merH deletion mutant suggested that the requirement for MerH could result from metal trafficking to the MerR transcription factor.
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Affiliation(s)
- James Schelert
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68508, USA
| | - Deepak Rudrappa
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68508, USA
| | - Tyler Johnson
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68508, USA
| | - Paul Blum
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68508, USA
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42
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Boyd ES, Barkay T. The mercury resistance operon: from an origin in a geothermal environment to an efficient detoxification machine. Front Microbiol 2012; 3:349. [PMID: 23087676 PMCID: PMC3466566 DOI: 10.3389/fmicb.2012.00349] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 09/11/2012] [Indexed: 11/21/2022] Open
Abstract
Mercuric mercury (Hg[II]) is a highly toxic and mobile element that is likely to have had a pronounced and adverse effect on biology since Earth’s oxygenation ∼2.4 billion years ago due to its high affinity for protein sulfhydryl groups, which upon binding destabilize protein structure and decrease enzyme activity, resulting in a decreased organismal fitness. The central enzyme in the microbial mercury detoxification system is the mercuric reductase (MerA) protein, which catalyzes the reduction of Hg(II) to volatile Hg(0). In addition to MerA, mer operons encode for proteins involved in regulation, Hg binding, and organomercury degradation. Mer-mediated approaches have had broad applications in the bioremediation of mercury-contaminated environments and industrial waste streams. Here, we examine the composition of 272 individual mer operons and quantitatively map the distribution of mer-encoded functions on both taxonomic SSU rRNA gene and MerA phylogenies. The results indicate an origin and early evolution of MerA among thermophilic bacteria and an overall increase in the complexity of mer operons through evolutionary time, suggesting continual gene recruitment and evolution leading to an improved efficiency and functional potential of the Mer detoxification system. Consistent with a positive relationship between the evolutionary history and topology of MerA and SSU rRNA gene phylogenies (Mantel R = 0.81, p < 0.01), the distribution of the majority of mer functions, when mapped on these phylograms, indicates an overall tendency to inherit mer-encoded functions through vertical descent. However, individual mer functions display evidence of a variable degree of vertical inheritance, with several genes exhibiting strong evidence for acquisition via lateral gene transfer and/or gene loss. Collectively, these data suggest that (i) mer has evolved from a simple system in geothermal environments to a widely distributed and more complex and efficient detoxification system, and (ii) merA is a suitable biomarker for examining the functional diversity of Hg detoxification and for predicting the composition of mer operons in natural environments.
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Affiliation(s)
- Eric S Boyd
- Department of Chemistry and Biochemistry, Montana State University Bozeman, MT, USA
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43
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Wallace BD, Edwards JS, Wallen JR, Moolman WJA, van der Westhuyzen R, Strauss E, Redinbo MR, Claiborne A. Turnover-dependent covalent inactivation of Staphylococcus aureus coenzyme A-disulfide reductase by coenzyme A-mimetics: mechanistic and structural insights. Biochemistry 2012; 51:7699-711. [PMID: 22954034 DOI: 10.1021/bi301026c] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Disruption of the unusual thiol-based redox homeostasis mechanisms in Staphylococcus aureus represents a unique opportunity to identify new metabolic processes and new targets for intervention. Targeting uncommon aspects of CoASH biosynthetic and redox functions in S. aureus, the antibiotic CJ-15,801 has recently been demonstrated to be an antimetabolite of the CoASH biosynthetic pathway in this organism; CoAS-mimetics containing α,β-unsaturated sulfone and carboxyl moieties have also been exploited as irreversible inhibitors of S. aureus coenzyme A-disulfide reductase (SaCoADR). In this work we have determined the crystal structures of three of these covalent SaCoADR-inhibitor complexes, prepared by inactivation of wild-type enzyme during turnover. The structures reveal the covalent linkage between the active-site Cys43-S(γ) and C(β) of the vinyl sulfone or carboxyl moiety. The full occupancy of two inhibitor molecules per enzyme dimer, together with kinetic analyses of the wild-type/C43S heterodimer, indicates that half-sites-reactivity is not a factor during normal catalytic turnover. Further, we provide the structures of SaCoADR active-site mutants; in particular, Tyr419'-OH plays dramatic roles in directing intramolecular reduction of the Cys43-SSCoA redox center, in the redox asymmetry observed for the two FAD per dimer in NADPH titrations, and in catalysis. The two conformations observed for the Ser43 side chain in the C43S mutant structure lend support to a conformational switch for Cys43-S(γ) during its catalytic Cys43-SSCoA/Cys43-SH redox cycle. Finally, the structures of the three inhibitor complexes provide a framework for design of more effective inhibitors with therapeutic potential against several major bacterial pathogens.
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Affiliation(s)
- Bret D Wallace
- Departments of Chemistry and Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
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44
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Allen RC, Tu YK, Nevarez MJ, Bobbs AS, Friesen JW, Lorsch JR, McCauley JA, Voet JG, Hamlett NV. The mercury resistance (mer) operon in a marine gliding flavobacterium, Tenacibaculum discolor 9A5. FEMS Microbiol Ecol 2012; 83:135-48. [PMID: 22816663 DOI: 10.1111/j.1574-6941.2012.01460.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 01/18/2023] Open
Abstract
Genes conferring mercury resistance have been investigated in a variety of bacteria and archaea but not in bacteria of the phylum Bacteroidetes, despite their importance in many environments. We found, however, that a marine gliding Bacteroidetes species, Tenacibaculum discolor, was the predominant mercury-resistant bacterial taxon cultured from a salt marsh fertilized with mercury-contaminated sewage sludge. Here we report characterization of the mercuric reductase and the narrow-spectrum mercury resistance (mer) operon from one of these strains - T. discolor 9A5. This mer operon, which confers mercury resistance when cloned into Flavobacterium johnsoniae, encodes a novel mercury-responsive ArsR/SmtB family transcriptional regulator that appears to have evolved independently from other mercury-responsive regulators, a novel putative transport protein consisting of a fusion between the integral membrane Hg(II) transporter MerT and the periplasmic Hg(II)-binding protein MerP, an additional MerP protein, and a mercuric reductase that is phylogenetically distinct from other known mercuric reductases.
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Affiliation(s)
- Rachel C Allen
- Program in Molecular Biology, Pomona College, Claremont, CA, USA
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45
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Mercury resistance and mercuric reductase activities and expression among chemotrophic thermophilic Aquificae. Appl Environ Microbiol 2012; 78:6568-75. [PMID: 22773655 DOI: 10.1128/aem.01060-12] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mercury (Hg) resistance (mer) by the reduction of mercuric to elemental Hg is broadly distributed among the Bacteria and Archaea and plays an important role in Hg detoxification and biogeochemical cycling. MerA is the protein subunit of the homodimeric mercuric reductase (MR) enzyme, the central function of the mer system. MerA sequences in the phylum Aquificae form the deepest-branching lineage in Bayesian phylogenetic reconstructions of all known MerA homologs. We therefore hypothesized that the merA homologs in two thermophilic Aquificae, Hydrogenobaculum sp. strain Y04AAS1 (AAS1) and Hydrogenivirga sp. strain 128-5-R1-1 (R1-1), specified Hg resistance. Results supported this hypothesis, because strains AAS1 and R1-1 (i) were resistant to >10 μM Hg(II), (ii) transformed Hg(II) to Hg(0) during cellular growth, and (iii) possessed Hg-dependent NAD(P)H oxidation activities in crude cell extracts that were optimal at temperatures corresponding with the strains' optimal growth temperatures, 55°C for AAS1 and 70°C for R1-1. While these characteristics all conformed with the mer system paradigm, expression of the Aquificae mer operons was not induced by exposure to Hg(II) as indicated by unity ratios of merA transcripts, normalized to gyrA transcripts for hydrogen-grown AAS1 cultures, and by similar MR specific activities in thiosulfate-grown cultures with and without Hg(II). The Hg(II)-independent expression of mer in the deepest-branching lineage of MerA from bacteria whose natural habitats are Hg-rich geothermal environments suggests that regulated expression of mer was a later innovation likely in environments where microorganisms were intermittently exposed to toxic concentrations of Hg.
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46
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Structural Characterization of Intramolecular Hg2+ Transfer between Flexibly Linked Domains of Mercuric Ion Reductase. J Mol Biol 2011; 413:639-56. [DOI: 10.1016/j.jmb.2011.08.042] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Revised: 08/20/2011] [Accepted: 08/22/2011] [Indexed: 11/20/2022]
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47
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Barkay T, Kritee K, Boyd E, Geesey G. A thermophilic bacterial origin and subsequent constraints by redox, light and salinity on the evolution of the microbial mercuric reductase. Environ Microbiol 2011; 12:2904-17. [PMID: 20545753 DOI: 10.1111/j.1462-2920.2010.02260.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Mercuric reductase (MerA) is central to the mercury (Hg) resistance (mer) system, catalyzing the reduction of ionic Hg to volatile Hg(0). A total of 213 merA homologues were identified in sequence databases, the majority of which belonged to microbial lineages that occupy oxic environments. merA was absent among phototrophs and in lineages that inhabit anoxic environments. Phylogenetic reconstructions of MerA indicate that (i) merA originated in a thermophilic bacterium following the divergence of the Archaea and Bacteria with a subsequent acquisition in Archaea via horizontal gene transfer (HGT), (ii) HGT of merA was rare across phylum boundaries and (iii) MerA from marine bacteria formed distinct and strongly supported lineages. Collectively, these observations suggest that a combination of redox, light and salinity conditions constrain MerA to microbial lineages that occupy environments where the most oxidized and toxic form of Hg, Hg(II), predominates. Further, the taxon-specific distribution of MerA with and without a 70 amino acid N-terminal extension may reflect intracellular levels of thiols. In conclusion, MerA likely evolved following the widespread oxygenation of the biosphere in a thermal environment and its subsequent evolution has been modulated by the interactions of Hg with the intra- and extracellular environment of the organism.
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Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers University, Lipman Hall, New Brunswick, NJ 08901, USA.
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48
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Hong B, Nauss R, Harwood IM, Miller SM. Direct measurement of mercury(II) removal from organomercurial lyase (MerB) by tryptophan fluorescence: NmerA domain of coevolved γ-proteobacterial mercuric ion reductase (MerA) is more efficient than MerA catalytic core or glutathione . Biochemistry 2010; 49:8187-96. [PMID: 20722420 DOI: 10.1021/bi100802k] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aerobic and facultative bacteria and archaea harboring mer loci exhibit resistance to the toxic effects of Hg(II) and organomercurials [RHg(I)]. In broad spectrum resistance, RHg(I) is converted to less toxic Hg(0) in the cytosol by the sequential action of organomercurial lyase (MerB: RHg(I) → RH + Hg(II)) and mercuric ion reductase (MerA: Hg(II) → Hg(0)) enzymes, requiring transfer of Hg(II) from MerB to MerA. Although previous studies with γ-proteobacterial versions of MerA and a nonphysiological Hg(II)-DTT-MerB complex qualitatively support a pathway for direct transfer between proteins, assessment of the relative efficiencies of Hg(II) transfer to the two different dicysteine motifs in γ-proteobacterial MerA and to competing cellular thiol is lacking. Here we show the intrinsic tryptophan fluorescence of γ-proteobacterial MerB is sensitive to Hg(II) binding and use this to probe the kinetics of Hg(II) removal from MerB by the N-terminal domain (NmerA) and catalytic core C-terminal cysteine pairs of its coevolved MerA and by glutathione (GSH), the major competing cellular thiol in γ-proteobacteria. At physiologically relevant concentrations, reaction with a 10-fold excess of NmerA over HgMerB removes ≥92% Hg(II), while similar extents of reaction require more than 1000-fold excess of GSH. Kinetically, the apparent second-order rate constant for Hg(II) transfer from MerB to NmerA, at (2.3 ± 0.1) × 10(4) M(-1) s(-1), is ∼100-fold greater than that for GSH ((1.2 ± 0.2) × 10(2) M(-1) s(-1)) or the MerA catalytic core (1.2 × 10(2) M(-1) s(-1)), establishing transfer to the metallochaperone-like NmerA domain as the kinetically favored pathway in this coevolved system.
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Affiliation(s)
- Baoyu Hong
- Department of Pharmaceutical Chemistry, University of California San Francisco,San Francisco, California 94158-2517, USA
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49
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Ledwidge R, Hong B, Dötsch V, Miller SM. NmerA of Tn501 Mercuric Ion Reductase: Structural Modulation of the pKa Values of the Metal Binding Cysteine Thiols,. Biochemistry 2010; 49:8988-98. [DOI: 10.1021/bi100537f] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Richard Ledwidge
- Department of Pharmaceutical Chemistry, University of California, San Francisco, 600 16th Street, San Francisco, California 94158-2517
| | - Baoyu Hong
- Department of Pharmaceutical Chemistry, University of California, San Francisco, 600 16th Street, San Francisco, California 94158-2517
| | - Volker Dötsch
- Institute of Biophysical Chemistry, Goethe University, Max-von-Laue Strasse 9, 60438 Frankfurt, Germany
| | - Susan M. Miller
- Department of Pharmaceutical Chemistry, University of California, San Francisco, 600 16th Street, San Francisco, California 94158-2517
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50
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Oliveira MA, Discola KF, Alves SV, Medrano FJ, Guimarães BG, Netto LES. Insights into the specificity of thioredoxin reductase-thioredoxin interactions. A structural and functional investigation of the yeast thioredoxin system. Biochemistry 2010; 49:3317-26. [PMID: 20235561 DOI: 10.1021/bi901962p] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The enzymatic activity of thioredoxin reductase enzymes is endowed by at least two redox centers: a flavin and a dithiol/disulfide CXXC motif. The interaction between thioredoxin reductase and thioredoxin is generally species-specific, but the molecular aspects related to this phenomenon remain elusive. Here, we investigated the yeast cytosolic thioredoxin system, which is composed of NADPH, thioredoxin reductase (ScTrxR1), and thioredoxin 1 (ScTrx1) or thioredoxin 2 (ScTrx2). We showed that ScTrxR1 was able to efficiently reduce yeast thioredoxins (mitochondrial and cytosolic) but failed to reduce the human and Escherichia coli thioredoxin counterparts. To gain insights into this specificity, the crystallographic structure of oxidized ScTrxR1 was solved at 2.4 A resolution. The protein topology of the redox centers indicated the necessity of a large structural rearrangement for FAD and thioredoxin reduction using NADPH. Therefore, we modeled a large structural rotation between the two ScTrxR1 domains (based on the previously described crystal structure, PDB code 1F6M ). Employing diverse approaches including enzymatic assays, site-directed mutagenesis, amino acid sequence alignment, and structure comparisons, insights were obtained about the features involved in the species-specificity phenomenon, such as complementary electronic parameters between the surfaces of ScTrxR1 and yeast thioredoxin enzymes and loops and residues (such as Ser(72) in ScTrx2). Finally, structural comparisons and amino acid alignments led us to propose a new classification that includes a larger number of enzymes with thioredoxin reductase activity, neglected in the low/high molecular weight classification.
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Affiliation(s)
- Marcos A Oliveira
- Departamento de Biologia, Universidade Estadual Paulista, São Vicente, Brazil
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