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Prakash D, Xiong J, Chauhan SS, Walters KA, Kruse H, Yennawar N, Golbeck JH, Guo Y, Ferry JG. Catalytic Activity of the Archetype from Group 4 of the FTR-like Ferredoxin:Thioredoxin Reductase Family Is Regulated by Unique S = 7/2 and S = 1/2 [4Fe-4S] Clusters. Biochemistry 2024; 63:1588-1598. [PMID: 38817151 PMCID: PMC11234629 DOI: 10.1021/acs.biochem.3c00651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2024]
Abstract
Thioredoxin reductases (TrxR) activate thioredoxins (Trx) that regulate the activity of diverse target proteins essential to prokaryotic and eukaryotic life. However, very little is understood of TrxR/Trx systems and redox control in methanogenic microbes from the domain Archaea (methanogens), for which genomes are abundant with annotations for ferredoxin:thioredoxin reductases [Fdx/thioredoxin reductase (FTR)] from group 4 of the widespread FTR-like family. Only two from the FTR-like family are characterized: the plant-type FTR from group 1 and FDR from group 6. Herein, the group 4 archetype (AFTR) from Methanosarcina acetivorans was characterized to advance understanding of the family and TrxR/Trx systems in methanogens. The modeled structure of AFTR, together with EPR and Mössbauer spectroscopies, supports a catalytic mechanism similar to plant-type FTR and FDR, albeit with important exceptions. EPR spectroscopy of reduced AFTR identified a transient [4Fe-4S]1+ cluster exhibiting a mixture of S = 7/2 and typical S = 1/2 signals, although rare for proteins containing [4Fe-4S] clusters, it is most likely the on-pathway intermediate in the disulfide reduction. Furthermore, an active site histidine equivalent to residues essential for the activity of plant-type FTR and FDR was found dispensable for AFTR. Finally, a unique thioredoxin system was reconstituted from AFTR, ferredoxin, and Trx2 from M. acetivorans, for which specialized target proteins were identified that are essential for growth and other diverse metabolisms.
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Affiliation(s)
- Divya Prakash
- School of Chemical and Biomolecular Sciences, Southern Illinois University-Carbondale, Carbondale, Illinois 62901, United States
| | - Jin Xiong
- Department of Chemistry, The Carnegie Mellon University, Pittsburgh,, Pennsylvania 15213, United States
| | - Shikha S Chauhan
- School of Chemical and Biomolecular Sciences, Southern Illinois University-Carbondale, Carbondale, Illinois 62901, United States
| | - Karim A Walters
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Hannah Kruse
- School of Chemical and Biomolecular Sciences, Southern Illinois University-Carbondale, Carbondale, Illinois 62901, United States
| | - Neela Yennawar
- The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - John H Golbeck
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Yisong Guo
- Department of Chemistry, The Carnegie Mellon University, Pittsburgh,, Pennsylvania 15213, United States
| | - James G Ferry
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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Yang G, Wijma HJ, Rozeboom HJ, Mascotti ML, Fraaije MW. Identification and characterization of archaeal and bacterial F 420 -dependent thioredoxin reductases. FEBS J 2023; 290:4777-4791. [PMID: 37403630 DOI: 10.1111/febs.16896] [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: 03/04/2023] [Revised: 06/19/2023] [Accepted: 07/04/2023] [Indexed: 07/06/2023]
Abstract
The thioredoxin pathway is an antioxidant system present in most organisms. Electrons flow from a thioredoxin reductase to thioredoxin at the expense of a specific electron donor. Most known thioredoxin reductases rely on NADPH as a reducing cofactor. Yet, in 2016, a new type of thioredoxin reductase was discovered in Archaea which utilize instead a reduced deazaflavin cofactor (F420 H2 ). For this reason, the respective enzyme was named deazaflavin-dependent flavin-containing thioredoxin reductase (DFTR). To have a broader understanding of the biochemistry of DFTRs, we identified and characterized two other archaeal representatives. A detailed kinetic study, which included pre-steady state kinetic analyses, revealed that these two DFTRs are highly specific for F420 H2 while displaying marginal activity with NADPH. Nevertheless, they share mechanistic features with the canonical thioredoxin reductases that are dependent on NADPH (NTRs). A detailed structural analysis led to the identification of two key residues that tune cofactor specificity of DFTRs. This allowed us to propose a DFTR-specific sequence motif that enabled for the first time the identification and experimental characterization of a bacterial DFTR.
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Affiliation(s)
- Guang Yang
- Molecular Enzymology Group, University of Groningen, The Netherlands
| | - Hein J Wijma
- Molecular Enzymology Group, University of Groningen, The Netherlands
| | | | - Maria Laura Mascotti
- Molecular Enzymology Group, University of Groningen, The Netherlands
- IMIBIO-SL CONICET, Facultad de Química Bioquímica y Farmacia, Universidad Nacional de San Luis, Argentina
| | - Marco W Fraaije
- Molecular Enzymology Group, University of Groningen, The Netherlands
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3
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A Reduced F 420-Dependent Nitrite Reductase in an Anaerobic Methanotrophic Archaeon. J Bacteriol 2022; 204:e0007822. [PMID: 35695516 PMCID: PMC9295563 DOI: 10.1128/jb.00078-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Anaerobic methanotrophic archaea (ANME), which oxidize methane in marine sediments through syntrophic associations with sulfate-reducing bacteria, carry homologs of coenzyme F420-dependent sulfite reductase (Fsr) of Methanocaldococcus jannaschii, a hyperthermophilic methanogen from deep-sea hydrothermal vents. M. jannaschii Fsr (MjFsr) and ANME-Fsr belong to two phylogenetically distinct groups, FsrI and FsrII, respectively. MjFsrI reduces sulfite to sulfide with reduced F420 (F420H2), protecting methyl coenzyme M reductase (Mcr), an essential enzyme for methanogens, from sulfite inhibition. However, the function of FsrIIs in ANME, which also rely on Mcr and live in sulfidic environments, is unknown. We have determined the catalytic properties of FsrII from a member of ANME-2c. Since ANME remain to be isolated, we expressed ANME2c-FsrII in a closely related methanogen, Methanosarcina acetivorans. Purified recombinant FsrII contained siroheme, indicating that the methanogen, which lacks a native sulfite reductase, produced this coenzyme. Unexpectedly, FsrII could not reduce sulfite or thiosulfate with F420H2. Instead, it acted as an F420H2-dependent nitrite reductase (FNiR) with physiologically relevant Km values (nitrite, 5 μM; F420H2, 14 μM). From kinetic, thermodynamic, and structural analyses, we hypothesize that in FNiR, F420H2-derived electrons are delivered at the oxyanion reduction site at a redox potential that is suitable for reducing nitrite (E0' [standard potential], +440 mV) but not sulfite (E0', -116 mV). These findings and the known nitrite sensitivity of Mcr suggest that FNiR may protect nondenitrifying ANME from nitrite toxicity. Remarkably, by reorganizing the reductant processing system, Fsr transforms two analogous oxyanions in two distinct archaeal lineages with different physiologies and ecologies. IMPORTANCE Coenzyme F420-dependent sulfite reductase (Fsr) protects methanogenic archaea inhabiting deep-sea hydrothermal vents from the inactivation of methyl coenzyme M reductase (Mcr), one of their essential energy production enzymes. Anaerobic methanotrophic archaea (ANME) that oxidize methane and rely on Mcr, carry Fsr homologs that form a distinct clade. We show that a member of this clade from ANME-2c functions as F420-dependent nitrite reductase (FNiR) and lacks Fsr activity. This specialization arose from a distinct feature of the reductant processing system and not the substrate recognition element. We hypothesize FNiR may protect ANME Mcr from inactivation by nitrite. This is an example of functional specialization within a protein family that is induced by changes in electron transfer modules to fit an ecological need.
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Structural and Biochemical Characterization of Thioredoxin-2 from Deinococcus radiodurans. Antioxidants (Basel) 2021; 10:antiox10111843. [PMID: 34829714 PMCID: PMC8615215 DOI: 10.3390/antiox10111843] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 11/17/2021] [Accepted: 11/18/2021] [Indexed: 12/19/2022] Open
Abstract
Thioredoxin (Trx), a ubiquitous protein showing disulfide reductase activity, plays critical roles in cellular redox control and oxidative stress response. Trx is a member of the Trx system, comprising Trx, Trx reductase (TrxR), and a cognate reductant (generally reduced nicotinamide adenine dinucleotide phosphate, NADPH). Bacterial Trx1 contains only the Trx-fold domain, in which the active site CXXC motif that is critical for the disulfide reduction activity is located. Bacterial Trx2 contains an N-terminal extension, which forms a zinc-finger domain, including two additional CXXC motifs. The multi-stress resistant bacterium Deinococcus radiodurans encodes both Trx1 (DrTrx1) and Trx2 (DrTrx2), which act as members of the enzymatic antioxidant systems. In this study, we constructed Δdrtrx1 and Δdrtrx2 mutants and examined their survival rates under H2O2 treated conditions. Both drtrx1 and drtrx2 genes were induced following H2O2 treatment, and the Δdrtrx1 and Δdrtrx2 mutants showed a decrease in resistance toward H2O2, compared to the wild-type. Native DrTrx1 and DrTrx2 clearly displayed insulin and DTNB reduction activity, whereas mutant DrTrx1 and DrTrx2, which harbors the substitution of conserved cysteine to serine in its active site CXXC motif, showed almost no reduction activity. Mutations in the zinc binding cysteines did not fully eliminate the reduction activities of DrTrx2. Furthermore, we solved the crystal structure of full-length DrTrx2 at 1.96 Å resolution. The N-terminal zinc-finger domain of Trx2 is thought to be involved in Trx-target interaction and, from our DrTrx2 structure, the orientation of the zinc-finger domain of DrTrx2 and its interdomain interaction, between the Trx-fold domain and the zinc-finger domain, is clearly distinguished from those of the other Trx2 structures.
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Grinter R, Greening C. Cofactor F420: an expanded view of its distribution, biosynthesis and roles in bacteria and archaea. FEMS Microbiol Rev 2021; 45:fuab021. [PMID: 33851978 PMCID: PMC8498797 DOI: 10.1093/femsre/fuab021] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Accepted: 04/11/2021] [Indexed: 12/11/2022] Open
Abstract
Many bacteria and archaea produce the redox cofactor F420. F420 is structurally similar to the cofactors FAD and FMN but is catalytically more similar to NAD and NADP. These properties allow F420 to catalyze challenging redox reactions, including key steps in methanogenesis, antibiotic biosynthesis and xenobiotic biodegradation. In the last 5 years, there has been much progress in understanding its distribution, biosynthesis, role and applications. Whereas F420 was previously thought to be confined to Actinobacteria and Euryarchaeota, new evidence indicates it is synthesized across the bacterial and archaeal domains, as a result of extensive horizontal and vertical biosynthetic gene transfer. F420 was thought to be synthesized through one biosynthetic pathway; however, recent advances have revealed variants of this pathway and have resolved their key biosynthetic steps. In parallel, new F420-dependent biosynthetic and metabolic processes have been discovered. These advances have enabled the heterologous production of F420 and identified enantioselective F420H2-dependent reductases for biocatalysis. New research has also helped resolve how microorganisms use F420 to influence human and environmental health, providing opportunities for tuberculosis treatment and methane mitigation. A total of 50 years since its discovery, multiple paradigms associated with F420 have shifted, and new F420-dependent organisms and processes continue to be discovered.
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Affiliation(s)
- Rhys Grinter
- Department of Microbiology, Monash Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia
| | - Chris Greening
- Department of Microbiology, Monash Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia
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6
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Mascotti ML, Juri Ayub M, Fraaije MW. On the diversity of F 420 -dependent oxidoreductases: A sequence- and structure-based classification. Proteins 2021; 89:1497-1507. [PMID: 34216160 PMCID: PMC8518648 DOI: 10.1002/prot.26170] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 03/30/2021] [Accepted: 06/26/2021] [Indexed: 11/05/2022]
Abstract
The F420 deazaflavin cofactor is an intriguing molecule as it structurally resembles the canonical flavin cofactor, although behaves as a nicotinamide cofactor due to its obligate hydride-transfer reactivity and similar low redox potential. Since its discovery, numerous enzymes relying on it have been described. The known deazaflavoproteins are taxonomically restricted to Archaea and Bacteria. The biochemistry of the deazaflavoenzymes is diverse and they exhibit great structural variability. In this study a thorough sequence and structural homology evolutionary analysis was performed in order to generate an overarching classification of the F420 -dependent oxidoreductases. Five different deazaflavoenzyme Classes (I-V) are described according to their structural folds as follows: Class I encompassing the TIM-barrel F420 -dependent enzymes; Class II including the Rossmann fold F420 -dependent enzymes; Class III comprising the β-roll F420 -dependent enzymes; Class IV which exclusively gathers the SH3 barrel F420 -dependent enzymes and Class V including the three layer ββα sandwich F420 -dependent enzymes. This classification provides a framework for the identification and biochemical characterization of novel deazaflavoenzymes.
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Affiliation(s)
- María Laura Mascotti
- Molecular Enzymology Group, University of Groningen, Groningen, The Netherlands.,IMIBIO-SL CONICET, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina
| | - Maximiliano Juri Ayub
- IMIBIO-SL CONICET, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, San Luis, Argentina
| | - Marco W Fraaije
- Molecular Enzymology Group, University of Groningen, Groningen, The Netherlands
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7
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Chun HL, Chang YJ, Park HH. Crystal structure of the cofactor-free form of thioredoxin reductase from Acinetobacter baumannii. FEBS Lett 2021; 595:1977-1986. [PMID: 34118067 DOI: 10.1002/1873-3468.14149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 06/02/2021] [Accepted: 06/07/2021] [Indexed: 11/09/2022]
Abstract
Thioredoxin reductase (TrxR) is a central component in the thioredoxin system by involving in catalyzing the reduction of thioredoxin, which is critical for organism survival. Because this system is essential, it is a promising target for novel antimicrobial agents. Herein, we solved the 1.9 Å high-resolution structure of TrxR from Acinetobacter baumannii Thioredoxin reductase (AbTrxR), which is a Gram-negative, pathogenic bacterium and a drug-resistant superbug. AbTrxR was cofactor-free and formed a dimer in solution. AbTrxR contained a longer dimerization loop2 and a shorter β7 -β8 connecting loop than other TrxRs. AbTrxR cofactor-free form exhibited a flavin-oxidizing (FO) conformation, whose NADPH domain was located close to the dimeric interface. This structural information might be helpful for development of new antibiotic agents targeting superbugs.
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Affiliation(s)
- Hye Lin Chun
- College of Pharmacy, Chung-Ang University, Seoul, Korea.,Department of Global Innovative Drugs, Graduate School of Chung-Ang University, Seoul, Korea
| | - Ye Ji Chang
- College of Pharmacy, Chung-Ang University, Seoul, Korea.,Department of Global Innovative Drugs, Graduate School of Chung-Ang University, Seoul, Korea
| | - Hyun Ho Park
- College of Pharmacy, Chung-Ang University, Seoul, Korea.,Department of Global Innovative Drugs, Graduate School of Chung-Ang University, Seoul, Korea
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Buey RM, Fernández-Justel D, González-Holgado G, Martínez-Júlvez M, González-López A, Velázquez-Campoy A, Medina M, Buchanan BB, Balsera M. Unexpected diversity of ferredoxin-dependent thioredoxin reductases in cyanobacteria. PLANT PHYSIOLOGY 2021; 186:285-296. [PMID: 33599267 PMCID: PMC8154056 DOI: 10.1093/plphys/kiab072] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 01/31/2021] [Indexed: 06/12/2023]
Abstract
Thioredoxin reductases control the redox state of thioredoxins (Trxs)-ubiquitous proteins that regulate a spectrum of enzymes by dithiol-disulfide exchange reactions. In most organisms, Trx is reduced by NADPH via a thioredoxin reductase flavoenzyme (NTR), but in oxygenic photosynthetic organisms, this function can also be performed by an iron-sulfur ferredoxin (Fdx)-dependent thioredoxin reductase (FTR) that links light to metabolic regulation. We have recently found that some cyanobacteria, such as the thylakoid-less Gloeobacter and the ocean-dwelling green oxyphotobacterium Prochlorococcus, lack NTR and FTR but contain a thioredoxin reductase flavoenzyme (formerly tentatively called deeply-rooted thioredoxin reductase or DTR), whose electron donor remained undefined. Here, we demonstrate that Fdx functions in this capacity and report the crystallographic structure of the transient complex between the plant-type Fdx1 and the thioredoxin reductase flavoenzyme from Gloeobacter violaceus. Thereby, our data demonstrate that this cyanobacterial enzyme belongs to the Fdx flavin-thioredoxin reductase (FFTR) family, originally described in the anaerobic bacterium Clostridium pasteurianum. Accordingly, the enzyme hitherto termed DTR is renamed FFTR. Our experiments further show that the redox-sensitive peptide CP12 is modulated in vitro by the FFTR/Trx system, demonstrating that FFTR functionally substitutes for FTR in light-linked enzyme regulation in Gloeobacter. Altogether, we demonstrate the FFTR is spread within the cyanobacteria phylum and propose that, by substituting for FTR, it connects the reduction of target proteins to photosynthesis. Besides, the results indicate that FFTR acquisition constitutes a mechanism of evolutionary adaptation in marine phytoplankton such as Prochlorococcus that live in low-iron environments.
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Affiliation(s)
- Rubén M Buey
- Metabolic Engineering Group, Departamento de Microbiología y Genética, Universidad de Salamanca, Salamanca 37007, Spain
| | - David Fernández-Justel
- Metabolic Engineering Group, Departamento de Microbiología y Genética, Universidad de Salamanca, Salamanca 37007, Spain
| | - Gloria González-Holgado
- Department of Abiotic Stress, Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), Salamanca 37008, Spain
| | - Marta Martínez-Júlvez
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Instituto de Biocomputación y Física de Sistemas Complejos (GBsC-CSIC and BIFI-IQFR Joint Units), Universidad de Zaragoza, Zaragoza 50018, Spain
| | - Adrián González-López
- Department of Abiotic Stress, Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), Salamanca 37008, Spain
| | - Adrián Velázquez-Campoy
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Instituto de Biocomputación y Física de Sistemas Complejos (GBsC-CSIC and BIFI-IQFR Joint Units), Universidad de Zaragoza, Zaragoza 50018, Spain
- Aragon Institute for Health Research (IIS-Aragon), Zaragoza 50009, Spain
- Biomedical Research Networking Center in Digestive and Hepatic Diseases (CIBERehd), Madrid 28029, Spain
- Fundación ARAID, Government of Aragon, Zaragoza, Spain, Department of Plant & Microbial Biology, University of California, Berkeley, CA 94708, USA
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Instituto de Biocomputación y Física de Sistemas Complejos (GBsC-CSIC and BIFI-IQFR Joint Units), Universidad de Zaragoza, Zaragoza 50018, Spain
| | - Bob B Buchanan
- Biomedical Research Networking Center in Digestive and Hepatic Diseases (CIBERehd), Madrid 28029, Spain
| | - Monica Balsera
- Department of Abiotic Stress, Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), Salamanca 37008, Spain
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Rawat M, Maupin-Furlow JA. Redox and Thiols in Archaea. Antioxidants (Basel) 2020; 9:antiox9050381. [PMID: 32380716 PMCID: PMC7278568 DOI: 10.3390/antiox9050381] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 04/30/2020] [Accepted: 05/02/2020] [Indexed: 12/11/2022] Open
Abstract
Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.
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Affiliation(s)
- Mamta Rawat
- Biology Department, California State University, Fresno, CA 93740, USA
- Correspondence: (M.R.); (J.A.M.-F.)
| | - Julie A. Maupin-Furlow
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA
- Genetics Institute, University of Florida, Gainesville, FL 32611, USA
- Correspondence: (M.R.); (J.A.M.-F.)
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10
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Balsera M, Buchanan BB. Evolution of the thioredoxin system as a step enabling adaptation to oxidative stress. Free Radic Biol Med 2019; 140:28-35. [PMID: 30862542 DOI: 10.1016/j.freeradbiomed.2019.03.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 02/27/2019] [Accepted: 03/05/2019] [Indexed: 01/08/2023]
Abstract
Thioredoxins (Trxs) are low-molecular-weight proteins that participate in the reduction of target enzymes. Trxs contain a redox-active disulfide bond, in the form of a WCGPC amino acid sequence motif, that enables them to perform dithiol-disulfide exchange reactions with oxidized protein substrates. Widely distributed across the three domains of life, Trxs form an evolutionarily conserved family of ancient origin. Thioredoxin reductases (TRs) are enzymes that reduce Trxs. According to their evolutionary history, TRs have diverged, thereby leading to the emergence of variants of the enzyme that in combination with different types of Trxs meet the needs of the cell. In addition to participating in the regulation of metabolism and defense against oxidative stress, Trxs respond to environmental signals-an ability that developed early in evolution. Redox regulation of proteins targeted by Trx is accomplished with a pair of redox-active cysteines located in strategic positions on the polypeptide chain to enable reversible oxidative changes that result in structural and functional modifications target proteins. In this review, we present a general overview of the thioredoxin system and describe recent structural studies on the diversity of its components.
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Affiliation(s)
- Monica Balsera
- Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), 37008 Salamanca, Spain.
| | - Bob B Buchanan
- Department of Plant & Microbial Biology, University of California, Berkeley, 94720 CA, USA.
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11
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Susanti D, Frazier MC, Mukhopadhyay B. A Genetic System for Methanocaldococcus jannaschii: An Evolutionary Deeply Rooted Hyperthermophilic Methanarchaeon. Front Microbiol 2019; 10:1256. [PMID: 31333590 PMCID: PMC6616113 DOI: 10.3389/fmicb.2019.01256] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Accepted: 05/20/2019] [Indexed: 12/20/2022] Open
Abstract
Phylogenetically deeply rooted methanogens belonging to the genus of Methanocaldococcus living in deep-sea hydrothermal vents derive energy exclusively from hydrogenotrophic methanogenesis, one of the oldest respiratory metabolisms on Earth. These hyperthermophilic, autotrophic archaea synthesize their biomolecules from inorganic substrates and perform high temperature biocatalysis producing methane, a valuable fuel and potent greenhouse gas. The information processing and stress response systems of archaea are highly homologous to those of the eukaryotes. For this broad relevance, Methanocaldococcus jannaschii, the first hyperthermophilic chemolithotrophic organism that was isolated from a deep-sea hydrothermal vent, was also the first archaeon and third organism for which the whole genome sequence was determined. The research that followed uncovered numerous novel information in multiple fields, including those described above. M. jannaschii was found to carry ancient redox control systems, precursors of dissimilatory sulfate reduction enzymes, and a eukaryotic-like protein translocation system. It provided a platform for structural genomics and tools for incorporating unnatural amino acids into proteins. However, the assignments of in vivo relevance to these findings or interrogations of unknown aspects of M. jannaschii through genetic manipulations remained out of reach, as the organism was genetically intractable. This report presents tools and methods that remove this block. It is now possible to knockout or modify a gene in M. jannaschii and genetically fuse a gene with an affinity tag sequence, thereby allowing facile isolation of a protein with M. jannaschii-specific attributes. These tools have helped to genetically validate the role of a novel coenzyme F420-dependent sulfite reductase in conferring resistance to sulfite in M. jannaschii and to demonstrate that the organism possesses a deazaflavin-dependent system for neutralizing oxygen.
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Affiliation(s)
- Dwi Susanti
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, United States
| | - Mary C Frazier
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, United States
| | - Biswarup Mukhopadhyay
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, United States.,Biocomplexity Institute, Virginia Tech, Blacksburg, VA, United States.,Virginia Tech Carilion School of Medicine, Virginia Tech, Blacksburg, VA, United States
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12
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Lyu Z, Whitman WB. Transplanting the pathway engineering toolbox to methanogens. Curr Opin Biotechnol 2019; 59:46-54. [PMID: 30875664 DOI: 10.1016/j.copbio.2019.02.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 01/30/2019] [Accepted: 02/09/2019] [Indexed: 10/27/2022]
Abstract
Biological methanogenesis evolved early in Earth's history and was likely already a major process by 3.5 Ga. Modern methanogenesis is now a key process in virtually all anaerobic microbial communities, such as marine and lake sediments, wetland and rice soils, and human and cattle digestive tracts. Owing to their long evolution and extensive adaptations to various habitats, methanogens possess enormous metabolic and physiological diversity. Not only does this diversity offers unique opportunities for biotechnology applications, but also reveals their direct impact on the environment, agriculture, and human and animal health. These efforts are facilitated by an advanced genetic toolbox, emerging new molecular tools, and systems-level modelling for methanogens. Further developments and convergence of these technical advancements provide new opportunities for bioengineering methanogens.
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Affiliation(s)
- Zhe Lyu
- Department of Microbiology, University of Georgia, Athens, GA 30602, USA
| | - William B Whitman
- Department of Microbiology, University of Georgia, Athens, GA 30602, USA.
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13
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Ferredoxin-linked flavoenzyme defines a family of pyridine nucleotide-independent thioredoxin reductases. Proc Natl Acad Sci U S A 2018; 115:12967-12972. [PMID: 30510005 DOI: 10.1073/pnas.1812781115] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ferredoxin-dependent thioredoxin reductase was identified 35 y ago in the fermentative bacterium Clostridium pasteurianum [Hammel KE, Cornwell KL, Buchanan BB (1983) Proc Natl Acad Sci USA 80:3681-3685]. The enzyme, a flavoprotein, was strictly dependent on ferredoxin as reductant and was inactive with either NADPH or NADH. This early work has not been further pursued. We have recently reinvestigated the problem and confirmed that the enzyme, here designated ferredoxin-dependent flavin thioredoxin reductase (FFTR), is a flavoprotein. The enzyme differs from ferredoxin-thioredoxin reductase (FTR), which has a signature [4Fe-4S] cluster, but shows structural similarities to NADP-dependent thioredoxin reductase (NTR). Comparative amino acid sequence analysis showed that FFTR is present in a number of clostridial species, some of which lack both FTR and an archetypal NTR. We have isolated, crystallized, and determined the structural properties of FFTR from a member of this group, Clostridium acetobutylicum, both alone and in complex with Trx. The structures showed an elongated FFTR homodimer, each monomer comprising two Rossmann domains and a noncovalently bound FAD cofactor that exposes the isoalloxazine ring to the solvent. The FFTR structures revealed an alternative domain organization compared with NTR that enables the enzyme to accommodate Fdx rather than NADPH. The results suggest that FFTR exists in a range of conformations with varying degrees of domain separation in solution and that the stacking between the two redox-active groups for the transfer of reducing equivalents results in a profound structural reorganization. A mechanism in accord with the findings is proposed.
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14
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Buey RM, Schmitz RA, Buchanan BB, Balsera M. Crystal Structure of the Apo-Form of NADPH-Dependent Thioredoxin Reductase from a Methane-Producing Archaeon. Antioxidants (Basel) 2018; 7:E166. [PMID: 30453601 PMCID: PMC6262447 DOI: 10.3390/antiox7110166] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 11/12/2018] [Accepted: 11/14/2018] [Indexed: 12/20/2022] Open
Abstract
The redox regulation of proteins via reversible dithiol/disulfide exchange reactions involves the thioredoxin system, which is composed of a reductant, a thioredoxin reductase (TR), and thioredoxin (Trx). In the pyridine nucleotide-dependent Trx reduction pathway, reducing equivalents, typically from reduced nicotinamide adenine dinucleotide phosphate (NADPH), are transferred from NADPH-TR (NTR) to Trx and, in turn, to target proteins, thus resulting in the reversible modification of the structural and functional properties of the targets. NTR enzymes contain three functional sites: an NADPH binding pocket, a non-covalently bound flavin cofactor, and a redox-active disulfide in the form of CxxC. With the aim of increasing our knowledge of the thioredoxin system in archaea, we here report the high-resolution crystal structure of NTR from the methane-generating organism Methanosarcina mazei strain Gö1 (MmNTR) at 2.6 Å resolution. Based on the crystals presently described, MmNTR assumes an overall fold that is nearly identical to the archetypal fold of authentic NTRs; however, surprisingly, we observed no electron density for flavin adenine dinucleotide (FAD) despite the well-defined and conserved FAD-binding cavity in the folded module. Remarkably, the dimers of the apo-protein within the crystal were different from those observed by small angle X-ray scattering (SAXS) for the holo-protein, suggesting that the binding of the flavin cofactor does not require major protein structural rearrangements. Rather, binding results in the stabilization of essential parts of the structure, such as those involved in dimer stabilization. Altogether, this structure represents the example of an apo-form of an NTR that yields important insight into the effects of the cofactor on protein folding.
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Affiliation(s)
- Rubén M Buey
- Metabolic Engineering Group. Dpto. Microbiología y Genética. Universidad de Salamanca, 37007 Salamanca, Spain.
| | - Ruth A Schmitz
- Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität Kiel, 24118 Kiel, Germany.
| | - Bob B Buchanan
- Department of Plant & Microbial Biology, University of California, 94720 Berkeley CA, USA.
| | - Monica Balsera
- Instituto de Recursos Naturales y Agrobiología de Salamanca (IRNASA-CSIC), 37008 Salamanca, Spain.
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15
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Coenzyme F 420-Dependent Glucose-6-Phosphate Dehydrogenase-Coupled Polyglutamylation of Coenzyme F 420 in Mycobacteria. J Bacteriol 2018; 200:JB.00375-18. [PMID: 30249701 DOI: 10.1128/jb.00375-18] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 09/07/2018] [Indexed: 12/15/2022] Open
Abstract
Coenzyme F420 plays a key role in the redox metabolisms of various archaea and bacteria, including Mycobacterium tuberculosis In M. tuberculosis, F420-dependent reactions have been linked to several virulence factors. F420 carries multiple glutamate residues in the side chain, forming F420-n species (n, number of glutamate residues), and the length of this side chain impacts cellular physiology. M. tuberculosis strains with F420 species carrying shorter side chains exhibit resistance to delamanid and pretomanid, two new tuberculosis (TB) drugs. Thus, the process of polyglutamylation of F420 is of great interest. It has been known from genetic analysis that in mycobacteria an F420-0 γ-glutamyl ligase (FbiB) introduces up to seven glutamate residues into F420 However, purified FbiB of M. tuberculosis (MtbFbiB) is either inefficient or incapable of incorporating more than two glutamates. We found that, in vitro, MtbFbiB synthesized side chains containing up to seven glutamate residues if F420 was presented to the enzyme in a two-electron reduced state (F420H2). Our genetic analysis in Mycobacterium bovis BCG and Mycobacterium smegmatis and an analysis of literature data on M. tuberculosis revealed that in these mycobacteria the polyglutamylation process requires the assistance of F420-dependent glucose-6-phosphate dehydrogenase (Fgd) which reduces F420 to F420H2 We hypothesize that, starting with F420-0H2, the amino-terminal domain of FbiB builds F420-2H2, which is then transferred to the carboxy-terminal domain for further glutamylation; F420-2H2 modifies the carboxy-terminal domain structurally to accommodate longer glutamyl chains. This system is analogous to folylpolyglutamate synthase, which introduces more than one glutamate residue into folate only after this vitamin is reduced to tetrahydrofolate.IMPORTANCE Coenzyme F420-dependent reactions of Mycobacterium tuberculosis, which causes tuberculosis, potentially contributes to the virulence of this bacterium. The coenzyme carries a glutamic acid-derived tail, the length of which influences the metabolism of M. tuberculosis Mutations that eliminate the production of F420 with longer tails make M. tuberculosis resistant to two new tuberculosis drugs. This report describes that the synthesis of longer glutamyl tails of F420 requires concerted actions of two enzymes, one of which reduces the coenzyme prior to the action of the other, which catalyzes polyglutamylation. This knowledge will help to develop more effective tuberculosis (TB) drugs. Remarkably, the introduction of multiple glutamate residues into the sidechain of folate (vitamin B9) requires similar concerted actions, where one enzyme reduces the vitamin to tetrahydrofolate and the other catalyzes polyglutamylation; folate is required for DNA and amino acid synthesis. Thus, the reported research has also revealed a key similarity between two important cellular systems.
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16
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Methionine Sulfoxide Reductases of Archaea. Antioxidants (Basel) 2018; 7:antiox7100124. [PMID: 30241308 PMCID: PMC6211008 DOI: 10.3390/antiox7100124] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 09/05/2018] [Accepted: 09/11/2018] [Indexed: 01/04/2023] Open
Abstract
Methionine sulfoxide reductases are found in all domains of life and are important in reversing the oxidative damage of the free and protein forms of methionine, a sulfur containing amino acid particularly sensitive to reactive oxygen species (ROS). Archaea are microbes of a domain of life distinct from bacteria and eukaryotes. Archaea are well known for their ability to withstand harsh environmental conditions that range from habitats of high ROS, such as hypersaline lakes of intense ultraviolet (UV) radiation and desiccation, to hydrothermal vents of low concentrations of dissolved oxygen at high temperature. Recent evidence reveals the methionine sulfoxide reductases of archaea function not only in the reduction of methionine sulfoxide but also in the ubiquitin-like modification of protein targets during oxidative stress, an association that appears evolutionarily conserved in eukaryotes. Here is reviewed methionine sulfoxide reductases and their distribution and function in archaea.
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17
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Lyu Z, Lu Y. Metabolic shift at the class level sheds light on adaptation of methanogens to oxidative environments. ISME JOURNAL 2017; 12:411-423. [PMID: 29135970 PMCID: PMC5776455 DOI: 10.1038/ismej.2017.173] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 07/31/2017] [Accepted: 08/09/2017] [Indexed: 11/09/2022]
Abstract
Methanogens have long been considered strictly anaerobic and oxygen-sensitive microorganisms, but their ability to survive oxygen stress has also been documented. Indeed, methanogens have been found in oxidative environments, and antioxidant genes have been detected in their genomes. How methanogens adapt to oxidative environments, however, remain poorly understood. Here, we systematically predicted and annotated antioxidant features from representative genomes across six well-established methanogen orders. Based on functional gene content involved in production of reactive oxygen species, Hierarchical Clustering analyses grouped methanogens into two distinct clusters, corresponding to the Class I and II methanogens, respectively. Comparative genomics suggested a systematic shift in metabolisms across the two classes, resulting in an enrichment of antioxidant features in the Class II. Moreover, meta-analysis of 16 S rRNA gene sequences obtained from EnvDB indicated that members of Class II were more frequently recovered from microaerophilic and even oxic environments than the Class I members. Phylogenomic analysis suggested that the Class I and II methanogens might have evolved before and around the Great Oxygenation Event, respectively. The enrichment of antioxidant features in the Class II methanogens may have played a key role in the adaption of this group to oxidative environments today and historically.
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Affiliation(s)
- Zhe Lyu
- College of Resources and Environmental Sciences, China Agricultural University, Beijing, PR China.,Department of Microbiology, University of Georgia, Athens, GA, USA
| | - Yahai Lu
- College of Resources and Environmental Sciences, China Agricultural University, Beijing, PR China.,College of Urban and Environmental Sciences, Peking University, Beijing, PR China
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18
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Unprecedented pathway of reducing equivalents in a diflavin-linked disulfide oxidoreductase. Proc Natl Acad Sci U S A 2017; 114:12725-12730. [PMID: 29133410 DOI: 10.1073/pnas.1713698114] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Flavoproteins participate in a wide variety of physiologically relevant processes that typically involve redox reactions. Within this protein superfamily, there exists a group that is able to transfer reducing equivalents from FAD to a redox-active disulfide bridge, which further reduces disulfide bridges in target proteins to regulate their structure and function. We have identified a previously undescribed type of flavin enzyme that is exclusive to oxygenic photosynthetic prokaryotes and that is based on the primary sequence that had been assigned as an NADPH-dependent thioredoxin reductase (NTR). However, our experimental data show that the protein does not transfer reducing equivalents from flavins to disulfides as in NTRs but functions in the opposite direction. High-resolution structures of the protein from Gloeobacter violaceus and Synechocystis sp. PCC6803 obtained by X-ray crystallography showed two juxtaposed FAD molecules per monomer in redox communication with an active disulfide bridge in a variant of the fold adopted by NTRs. We have tentatively named the flavoprotein "DDOR" (diflavin-linked disulfide oxidoreductase) and propose that its activity is linked to a thiol-based transfer of reducing equivalents in bacterial membranes. These findings expand the structural and mechanistic repertoire of flavoenzymes with oxidoreductase activity and pave the way to explore new protein engineering approaches aimed at designing redox-active proteins for diverse biotechnological applications.
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19
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Valette O, Tran TTT, Cavazza C, Caudeville E, Brasseur G, Dolla A, Talla E, Pieulle L. Biochemical Function, Molecular Structure and Evolution of an Atypical Thioredoxin Reductase from Desulfovibrio vulgaris. Front Microbiol 2017; 8:1855. [PMID: 29033913 PMCID: PMC5627308 DOI: 10.3389/fmicb.2017.01855] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 09/11/2017] [Indexed: 11/19/2022] Open
Abstract
Thioredoxin reductase (TR) regulates the intracellular redox environment by reducing thioredoxin (Trx). In anaerobes, recent findings indicate that the Trx redox network is implicated in the global redox regulation of metabolism but also actively participates in protecting cells against O2. In the anaerobe Desulfovibrio vulgaris Hildenborough (DvH), there is an intriguing redundancy of the Trx system which includes a classical system using NADPH as electron source, a non-canonical system using NADH and an isolated TR (DvTRi). The functionality of DvTRi was questioned due to its lack of reactivity with DvTrxs. Structural analysis shows that DvTRi is a NAD(P)H-independent TR but its reducer needs still to be identified. Moreover, DvTRi reduced by an artificial electron source is able to reduce in turn DvTrx1 and complexation experiments demonstrate a direct interaction between DvTRi and DvTrx1. The deletion mutant tri exhibits a higher sensitivity to disulfide stress and the gene tri is upregulated by O2 exposure. Having DvTRi in addition to DvTR1 as electron source for reducing DvTrx1 must be an asset to combat oxidative stress. Large-scale phylogenomics analyses show that TRi homologs are confined within the anaerobes. All TRi proteins displayed a conserved TQ/NGK motif instead of the HRRD motif, which is selective for the binding of the 2′-phosphate group of NADPH. The evolutionary history of TRs indicates that tr1 is the common gene ancestor in prokaryotes, affected by both gene duplications and horizontal gene events, therefore leading to the appearance of TRi through subfunctionalization over the evolutionary time.
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Affiliation(s)
| | - Tam T T Tran
- Aix-Marseille Univ, CNRS, LCB, Marseille, France
| | - Christine Cavazza
- Laboratoire de Chimie et Biologie des Métaux, Université Grenoble Alpes, Grenoble, France.,UMR 5249, Laboratoire de Chimie et Biologie des Métaux, Centre National de la Recherche Scientifique, Grenoble, France.,DRF/BIG/CBM, CEA-Grenoble, Grenoble, France
| | | | | | - Alain Dolla
- Aix-Marseille Univ, CNRS, LCB, Marseille, France
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20
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Susanti D, Loganathan U, Compton A, Mukhopadhyay B. A Reexamination of Thioredoxin Reductase from Thermoplasma acidophilum, a Thermoacidophilic Euryarchaeon, Identifies It as an NADH-Dependent Enzyme. ACS OMEGA 2017; 2:4180-4187. [PMID: 28884159 PMCID: PMC5579543 DOI: 10.1021/acsomega.7b00640] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 07/18/2017] [Indexed: 06/07/2023]
Abstract
Flavin-containing Trx reductase (TrxR) of Thermoplasma acidophilum (Ta), a thermoacidophilic facultative anaerobic archaeon, lacks the structural features for the binding of 2'-phosphate of nicotinamide adenine dinucleotide phosphate (NADPH), and this feature has justified the observed lack of activity with NADPH; NADH has also been reported to be ineffective. Our recent phylogenetic analysis identified Ta-TrxR as closely related to the NADH-dependent enzymes of Thermotoga maritima and Desulfovibrio vulgaris, both being anaerobic bacteria. This observation instigated a reexamination of the activity of the enzyme, which showed that Ta-TrxR is NADH dependent; the apparent Km for NADH was 3.1 μM, a physiologically relevant value. This finding is consistent with the observation that NADH:TrxR has thus far been found primarily in anaerobic bacteria and archaea.
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Affiliation(s)
- Dwi Susanti
- Department
of Biochemistry, Biocomplexity Institute, and Virginia Tech Carilion School of
Medicine, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Usha Loganathan
- Department
of Biochemistry, Biocomplexity Institute, and Virginia Tech Carilion School of
Medicine, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Austin Compton
- Department
of Biochemistry, Biocomplexity Institute, and Virginia Tech Carilion School of
Medicine, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Biswarup Mukhopadhyay
- Department
of Biochemistry, Biocomplexity Institute, and Virginia Tech Carilion School of
Medicine, Virginia Tech, Blacksburg, Virginia 24061, United States
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21
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McCarver AC, Lessner FH, Soroeta JM, Lessner DJ. Methanosarcina acetivorans utilizes a single NADPH-dependent thioredoxin system and contains additional thioredoxin homologues with distinct functions. MICROBIOLOGY-SGM 2017; 163:62-74. [PMID: 27902413 DOI: 10.1099/mic.0.000406] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The thioredoxin system plays a central role in the intracellular redox maintenance in the majority of cells. The canonical system consists of an NADPH-dependent thioredoxin reductase (TrxR) and thioredoxin (Trx), a disulfide reductase. Although Trx is encoded in almost all sequenced genomes of methanogens, its incorporation into their unique physiology is not well understood. Methanosarcina acetivorans contains a single TrxR (MaTrxR) and seven Trx (MaTrx1-MaTrx7) homologues. We previously showed that MaTrxR and at least MaTrx7 compose a functional NADPH-dependent thioredoxin system. Here, we report the characterization of all seven recombinant MaTrxs. MaTrx1, MaTrx3, MaTrx4 and MaTrx5 lack appreciable disulfide reductase activity, unlike previously characterized MaTrx2, MaTrx6 and MaTrx7. Enzyme assays demonstrated that, of the MaTrxs, only the reduction of disulfide-containing MaTrx7 is linked to the oxidation of reduced coenzymes. NADPH is shown to be supplied to the MaTrxR-MaTrx7 system through the oxidation of the primary methanogen electron carriers F420H2 and ferredoxin, indicating that it serves as a primary intracellular reducing system in M. acetivorans. Bioinformatic analyses also indicate that the majority of methanogens likely utilize an NADPH-dependent thioredoxin system. The remaining MaTrxs may have specialized functions. MaTrx1 and MaTrx3 exhibited thiol oxidase activity. MaTrx3 and MaTrx6 are targeted to the membrane of M. acetivorans and likely function in the formation and the reduction of disulfides in membrane and/or extracellular proteins, respectively. This work provides insight into the incorporation of Trx into the metabolism of methanogens, and this reveals that methanogens contain Trx homologues with alternative properties and activities.
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Affiliation(s)
- Addison C McCarver
- Department of Biological Sciences, University of Arkansas-Fayetteville, Fayetteville, AR 72701, USA
| | - Faith H Lessner
- Department of Biological Sciences, University of Arkansas-Fayetteville, Fayetteville, AR 72701, USA
| | - Jose M Soroeta
- Department of Biological Sciences, University of Arkansas-Fayetteville, Fayetteville, AR 72701, USA
| | - Daniel J Lessner
- Department of Biological Sciences, University of Arkansas-Fayetteville, Fayetteville, AR 72701, USA
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