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A thylakoid membrane-bound and redox-active rubredoxin (RBD1) functions in de novo assembly and repair of photosystem II. Proc Natl Acad Sci U S A 2019; 116:16631-16640. [PMID: 31358635 PMCID: PMC6697814 DOI: 10.1073/pnas.1903314116] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Photosystem II (PSII) catalyzes the light-driven oxidation of water in photosynthesis, supplying energy and oxygen to many life-forms on earth. During PSII assembly and repair, PSII intermediate complexes are prone to photooxidative damage, requiring mechanisms to minimize this damage. Here, we report the functional characterization of RBD1, a PSII assembly factor that interacts with PSII intermediate complexes to ensure their functional assembly and repair. We propose that the redox activity of RBD1 participates together with the cytochrome b559 to protect PSII from photooxidation. This work not only improves our understanding of cellular protection mechanisms for the vital PSII complex but also informs genetic engineering strategies for protection of PSII repair to increase agricultural productivity. Photosystem II (PSII) undergoes frequent photooxidative damage that, if not repaired, impairs photosynthetic activity and growth. How photosynthetic organisms protect vulnerable PSII intermediate complexes during de novo assembly and repair remains poorly understood. Here, we report the genetic and biochemical characterization of chloroplast-located rubredoxin 1 (RBD1), a PSII assembly factor containing a redox-active rubredoxin domain and a single C-terminal transmembrane α-helix (TMH) domain. RBD1 is an integral thylakoid membrane protein that is enriched in stroma lamellae fractions with the rubredoxin domain exposed on the stromal side. RBD1 also interacts with PSII intermediate complexes containing cytochrome b559. Complementation of the Chlamydomonas reinhardtii (hereafter Chlamydomonas) RBD1-deficient 2pac mutant with constructs encoding RBD1 protein truncations and site-directed mutations demonstrated that the TMH domain is essential for de novo PSII assembly, whereas the rubredoxin domain is involved in PSII repair. The rubredoxin domain exhibits a redox midpoint potential of +114 mV and is proficient in 1-electron transfers to a surrogate cytochrome c in vitro. Reduction of oxidized RBD1 is NADPH dependent and can be mediated by ferredoxin-NADP+ reductase (FNR) in vitro. We propose that RBD1 participates, together with the cytochrome b559, in the protection of PSII intermediate complexes from photooxidative damage during de novo assembly and repair. This role of RBD1 is consistent with its evolutionary conservation among photosynthetic organisms and the fact that it is essential in photosynthetic eukaryotes.
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Romão CV, Matias PM, Sousa CM, Pinho FG, Pinto AF, Teixeira M, Bandeiras TM. Insights into the Structures of Superoxide Reductases from the Symbionts Ignicoccus hospitalis and Nanoarchaeum equitans. Biochemistry 2018; 57:5271-5281. [PMID: 29939726 DOI: 10.1021/acs.biochem.8b00334] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Superoxide reductases (SORs) are enzymes that detoxify the superoxide anion through its reduction to hydrogen peroxide and exist in both prokaryotes and eukaryotes. The substrate is transformed at an iron catalytic center, pentacoordinated in the ferrous state by four histidines and one cysteine. SORs have a highly conserved motif, (E)(K)HxP-, in which the glutamate is associated with a redox-driven structural change, completing the octahedral coordination of the iron in the ferric state, whereas the lysine may be responsible for stabilization and donation of a proton to catalytic intermediates. We aimed to understand at the structural level the role of these two residues, by determining the X-ray structures of the SORs from the hyperthermophilic archaea Ignicoccus hospitalis and Nanoarchaeum equitans that lack the quasi-conserved lysine and glutamate, respectively, but have catalytic rate constants similar to those of the canonical enzymes, as we previously demonstrated. Furthermore, we have determined the crystal structure of the E23A mutant of I. hospitalis SOR, which mimics several enzymes that lack both residues. The structures revealed distinct structural arrangements of the catalytic center that simulate several catalytic cycle intermediates, namely, the reduced and the oxidized forms, and the glutamate-free and deprotonated ferric forms. Moreover, the structure of the I. hospitalis SOR provides evidence for the presence of an alternative lysine close to the iron center in the reduced state that may be a functional substitute for the "canonical" lysine.
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Affiliation(s)
- Célia V Romão
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Av. da República , 2780-157 Oeiras , Portugal
| | - Pedro M Matias
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Av. da República , 2780-157 Oeiras , Portugal.,iBET , Instituto de Biologia Experimental e Tecnológica , Apartado 12 , 2781-901 Oeiras , Portugal
| | - Cristiana M Sousa
- iBET , Instituto de Biologia Experimental e Tecnológica , Apartado 12 , 2781-901 Oeiras , Portugal
| | - Filipa G Pinho
- iBET , Instituto de Biologia Experimental e Tecnológica , Apartado 12 , 2781-901 Oeiras , Portugal
| | - Ana F Pinto
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Av. da República , 2780-157 Oeiras , Portugal
| | - Miguel Teixeira
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Av. da República , 2780-157 Oeiras , Portugal
| | - Tiago M Bandeiras
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Av. da República , 2780-157 Oeiras , Portugal.,iBET , Instituto de Biologia Experimental e Tecnológica , Apartado 12 , 2781-901 Oeiras , Portugal
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Maiti BK, Maia LB, Moro AJ, Lima JC, Cordas CM, Moura I, Moura JJG. Unusual Reduction Mechanism of Copper in Cysteine-Rich Environment. Inorg Chem 2018; 57:8078-8088. [PMID: 29956539 DOI: 10.1021/acs.inorgchem.8b00121] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Copper-cysteine interactions play an important role in Biology and herein we used the copper-substituted rubredoxin (Cu-Rd) from Desulfovibrio gigas to gain further insights into the copper-cysteine redox chemistry. EPR spectroscopy results are consistent with Cu-Rd harboring a CuII center in a sulfur-rich coordination, in a distorted tetrahedral structure ( g∥,⊥ = 2.183 and 2.032 and A∥,⊥ = 76.4 × 10-4 and 12 × 10-4 cm-1). In Cu-Rd, two oxidation states at Cu-center (CuII and CuI) are associated with Cys oxidation-reduction, alternating in the redox cycle, as pointed by electrochemical studies that suggest internal geometry rearrangements associated with the electron transfer processes. The midpoint potential of [CuI(S-Cys)2(Cys-S-S-Cys)]/[CuII(S-Cys)4] redox couple was found to be -0.15 V vs NHE showing a large separation of cathodic and anodic peaks potential (Δ Ep = 0.575 V). Interestingly, sulfur-rich CuII-Rd is highly stable under argon in dark conditions, which is thermodynamically unfavorable to Cu-thiol autoreduction. The reduction of copper and concomitant oxidation of Cys can both undergo two possible pathways: oxidative as well as photochemical. Under O2, CuII plays the role of the electron carrier from one Cys to O2 followed by internal geometry rearrangement at the Cu site, which facilitates reduction at Cu-center to yield CuI(S-Cys)2(Cys-S-S-Cys). Photoinduced (irradiated at λex = 280 nm) reduction of the CuII center is observed by UV-visible photolysis (above 300 nm all bands disappeared) and tryptophan fluorescence (∼335 nm peak enhanced) experiments. In both pathways, geometry reorganization plays an important role in copper reduction yielding an energetically compatible donor-acceptor system. This model system provides unusual stability and redox chemistry rather than the universal Cu-thiol auto redox chemistry in cysteine-rich copper complexes.
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Affiliation(s)
- Biplab K Maiti
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Luisa B Maia
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Artur J Moro
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - João C Lima
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Cristina M Cordas
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Isabel Moura
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - José J G Moura
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
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Mao Z, Liou SH, Khadka N, Jenney FE, Goodin DB, Seefeldt LC, Adams MWW, Cramer SP, Larsen DS. Cluster-Dependent Charge-Transfer Dynamics in Iron-Sulfur Proteins. Biochemistry 2018; 57:978-990. [PMID: 29303562 DOI: 10.1021/acs.biochem.7b01159] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photoinduced charge-transfer dynamics and the influence of cluster size on the dynamics were investigated using five iron-sulfur clusters: the 1Fe-4S cluster in Pyrococcus furiosus rubredoxin, the 2Fe-2S cluster in Pseudomonas putida putidaredoxin, the 4Fe-4S cluster in nitrogenase iron protein, and the 8Fe-7S P-cluster and the 7Fe-9S-1Mo FeMo cofactor in nitrogenase MoFe protein. Laser excitation promotes the iron-sulfur clusters to excited electronic states that relax to lower states. The electronic relaxation lifetimes of the 1Fe-4S, 8Fe-7S, and 7Fe-9S-1Mo clusters are on the picosecond time scale, although the dynamics of the MoFe protein is a mixture of the dynamics of the latter two clusters. The lifetimes of the 2Fe-2S and 4Fe-4S clusters, however, extend to several nanoseconds. A competition between reorganization energies and the density of electronic states (thus electronic coupling between states) mediates the charge-transfer lifetimes, with the 2Fe-2S cluster of Pdx and the 4Fe-4S cluster of Fe protein lying at the optimum leading to them having significantly longer lifetimes. Their long lifetimes make them the optimal candidates for long-range electron transfer and as external photosensitizers for other photoactivated chemical reactions like solar hydrogen production. Potential electron-transfer and hole-transfer pathways that possibly facilitate these charge transfers are proposed.
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Affiliation(s)
- Ziliang Mao
- Department of Chemistry, University of California at Davis , One Shields Avenue, Davis, California 95616, United States
| | - Shu-Hao Liou
- Department of Chemistry, University of California at Davis , One Shields Avenue, Davis, California 95616, United States
| | - Nimesh Khadka
- Department of Chemistry and Biochemistry, Utah State University , 0300 Old Main Hill, Logan, Utah 84322, United States
| | - Francis E Jenney
- Georgia Campus, Philadelphia College of Osteopathic Medicine , Suwanee, Georgia 30024, United States
| | - David B Goodin
- Department of Chemistry, University of California at Davis , One Shields Avenue, Davis, California 95616, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University , 0300 Old Main Hill, Logan, Utah 84322, United States
| | - Michael W W Adams
- Department of Biochemistry, The University of Georgia , Athens, Georgia 30602, United States
| | - Stephen P Cramer
- Department of Chemistry, University of California at Davis , One Shields Avenue, Davis, California 95616, United States
| | - Delmar S Larsen
- Department of Chemistry, University of California at Davis , One Shields Avenue, Davis, California 95616, United States
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5
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Romão CV, Vicente JB, Borges PT, Victor BL, Lamosa P, Silva E, Pereira L, Bandeiras TM, Soares CM, Carrondo MA, Turner D, Teixeira M, Frazão C. Structure of Escherichia coli Flavodiiron Nitric Oxide Reductase. J Mol Biol 2016; 428:4686-4707. [PMID: 27725182 DOI: 10.1016/j.jmb.2016.10.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 10/02/2016] [Accepted: 10/04/2016] [Indexed: 01/08/2023]
Abstract
Flavodiiron proteins (FDPs) are present in organisms from all domains of life and have been described so far to be involved in the detoxification of oxygen or nitric oxide (NO), acting as O2 and/or NO reductases. The Escherichia coli FDP, named flavorubredoxin (FlRd), is the most extensively studied FDP. Biochemical and in vivo studies revealed that FlRd is involved in NO detoxification as part of the bacterial defense mechanisms against reactive nitrogen species. E. coli FlRd has a clear preference for NO as a substrate in vitro, exhibiting a very low reactivity toward O2. To contribute to the understanding of the structural features defining this substrate selectivity, we determined the crystallographic structure of E. coli FlRd, both in the isolated and reduced states. The overall tetrameric structure revealed a highly conserved flavodiiron core domain, with a metallo-β-lactamase-like domain containing a diiron center, and a flavodoxin domain with a flavin mononucleotide cofactor. The metal center in the oxidized state has a μ-hydroxo bridge coordinating the two irons, while in the reduced state, this moiety is not detected. Since only the flavodiiron domain was observed in these crystal structures, the structure of the rubredoxin domain was determined by NMR. Tunnels for the substrates were identified, and through molecular dynamics simulations, no differences for O2 or NO permeation were found. The present data represent the first structure for a NO-selective FDP.
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Affiliation(s)
- Célia V Romão
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - João B Vicente
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Patrícia T Borges
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Bruno L Victor
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Pedro Lamosa
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Elísio Silva
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Luís Pereira
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Tiago M Bandeiras
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal; Instituto de Biologia Experimental e Tecnológica, Apartado 12, 2781-901 Oeiras, Portugal
| | - Cláudio M Soares
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Maria A Carrondo
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - David Turner
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal
| | - Miguel Teixeira
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal.
| | - Carlos Frazão
- Instituto de Tecnologia Química e Biológica António Xavier, ITQB NOVA, Av. da República, 2780-157 Oeiras, Portugal.
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Li Y, Liu P, Takano T, Liu S. A Chloroplast-Localized Rubredoxin Family Protein Gene from Puccinellia tenuiflora (PutRUB) Increases NaCl and NaHCO₃ Tolerance by Decreasing H₂O₂ Accumulation. Int J Mol Sci 2016; 17:ijms17060804. [PMID: 27248998 PMCID: PMC4926338 DOI: 10.3390/ijms17060804] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 05/13/2016] [Accepted: 05/18/2016] [Indexed: 11/24/2022] Open
Abstract
Rubredoxin is one of the simplest iron–sulfur (Fe–S) proteins. It is found primarily in strict anaerobic bacteria and acts as a mediator of electron transfer participation in different biochemical reactions. The PutRUB gene encoding a chloroplast-localized rubredoxin family protein was screened from a yeast full-length cDNA library of Puccinellia tenuiflora under NaCl and NaHCO3 stress. We found that PutRUB expression was induced by abiotic stresses such as NaCl, NaHCO3, CuCl2 and H2O2. These findings suggested that PutRUB might be involved in plant responses to adversity. In order to study the function of this gene, we analyzed the phenotypic and physiological characteristics of PutRUB transgenic plants treated with NaCl and NaHCO3. The results showed that PutRUB overexpression inhibited H2O2 accumulation, and enhanced transgenic plant adaptability to NaCl and NaHCO3 stresses. This indicated PutRUB might be involved in maintaining normal electron transfer to reduce reactive oxygen species (ROS) accumulation.
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Affiliation(s)
- Ying Li
- Key Laboratory of Saline-alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Harbin Hexing Road, Harbin 150040, China.
| | - Panpan Liu
- Key Laboratory of Saline-alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Harbin Hexing Road, Harbin 150040, China.
| | - Tetsuo Takano
- Asian Natural Environmental Science Center, University of Tokyo, Nishitokyo-shi, Tokyo 188-0002, Japan.
| | - Shenkui Liu
- Key Laboratory of Saline-alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Harbin Hexing Road, Harbin 150040, China.
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Horch M, Utesch T, Hildebrandt P, Mroginski MA, Zebger I. Domain motions and electron transfer dynamics in 2Fe-superoxide reductase. Phys Chem Chem Phys 2016; 18:23053-66. [DOI: 10.1039/c6cp03666j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Theoretical studies on 2Fe-superoxide reductase provide mechanistic insights into structural dynamics and electron transfer efficiencies.
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Affiliation(s)
- Marius Horch
- Institut für Chemie
- Technische Universität Berlin
- D-10623 Berlin
- Germany
| | - Tillmann Utesch
- Institut für Chemie
- Technische Universität Berlin
- D-10623 Berlin
- Germany
| | - Peter Hildebrandt
- Institut für Chemie
- Technische Universität Berlin
- D-10623 Berlin
- Germany
| | | | - Ingo Zebger
- Institut für Chemie
- Technische Universität Berlin
- D-10623 Berlin
- Germany
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Comparative electrochemical study of superoxide reductases. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:209-15. [PMID: 22143105 DOI: 10.1007/s00249-011-0777-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Revised: 10/29/2011] [Accepted: 11/21/2011] [Indexed: 10/15/2022]
Abstract
Superoxide reductases are involved in relevant biological electron transfer reactions related to protection against oxidative stress caused by reactive oxygen species. The electrochemical features of metalloproteins belonging to the three different classes of enzymes were studied by potentio-dynamic techniques (cyclic and square wave voltammetry): desulfoferrodoxin from Desulfovibrio vulgaris Hildenborough, class I superoxide reductases and neelaredoxin from Desulfovibrio gigas and Treponema pallidum, namely class II and III superoxide reductases, respectively. In addition, a small protein, designated desulforedoxin from D. gigas, which has high homology with the N-terminal domain of class I superoxide reductases, was also investigated. A comparison of the redox potentials and redox behavior of all the proteins is presented, and the results show that SOR center II is thermodynamically more stable than similar centers in different proteins, which may be related to an intramolecular electron transfer function.
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New spectroscopic and electrochemical insights on a class I superoxide reductase: evidence for an intramolecular electron-transfer pathway. Biochem J 2011; 438:485-94. [DOI: 10.1042/bj20110836] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
SORs (superoxide reductases) are enzymes involved in bacterial resistance to reactive oxygen species, catalysing the reduction of superoxide anions to hydrogen peroxide. So far three structural classes have been identified. Class I enzymes have two iron-centre-containing domains. Most studies have focused on the catalytic iron site (centre II), yet the role of centre I is poorly understood. The possible roles of this iron site were approached by an integrated study using both classical and fast kinetic measurements, as well as direct electrochemistry. A new heterometallic form of the protein with a zinc-substituted centre I, maintaining the iron active-site centre II, was obtained, resulting in a stable derivative useful for comparison with the native all-iron from. Second-order rate constants for the electron transfer between reduced rubredoxin and the different SOR forms were determined to be 2.8×107 M−1·s−1 and 1.3×106 M−1·s−1 for SORFe(IIII)-Fe(II) and for SORFe(IIII)-Fe(III) forms respectively, and 3.2×106 M−1·s−1 for the SORZn(II)-Fe(III) form. The results obtained seem to indicate that centre I transfers electrons from the putative physiological donor rubredoxin to the catalytic active iron site (intramolecular process). In addition, electrochemical results show that conformational changes are associated with the redox state of centre I, which may enable a faster catalytic response towards superoxide anion. The apparent rate constants calculated for the SOR-mediated electron transfer also support this observation.
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Bonnot F, Duval S, Lombard M, Valton J, Houée-Levin C, Nivière V. Intermolecular electron transfer in two-iron superoxide reductase: a putative role for the desulforedoxin center as an electron donor to the iron active site. J Biol Inorg Chem 2011; 16:889-98. [PMID: 21590471 DOI: 10.1007/s00775-011-0788-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Accepted: 04/19/2011] [Indexed: 10/18/2022]
Abstract
Superoxide reductase (SOR) is a superoxide detoxification system present in some microorganisms. Its active site consists of an unusual mononuclear iron center with an FeN4S1 coordination which catalyzes the one-electron reduction of superoxide to form hydrogen peroxide. Different classes of SORs have been described depending on the presence of an additional rubredoxin-like, desulforedoxin iron center, whose function has remained unknown until now. In this work, we investigated the mechanism of the reduction of the SOR iron active site using the NADPH:flavodoxin oxidoreductase from Escherichia coli, which was previously shown to efficiently transfer electrons to the Desulfoarculus baarsii SOR. When present, the additional rubredoxin-like iron center could function as an electronic relay between cellular reductases and the iron active site for superoxide reduction. This electron transfer was mainly intermolecular, between the rubredoxin-like iron center of one SOR and the iron active site of another SOR. These data provide the first experimental evidence for a possible role of the rubredoxin-like iron center in the superoxide detoxifying activity of SOR.
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Affiliation(s)
- Florence Bonnot
- Laboratoire de Chimie et Biologie des Métaux, iRTSV-CEA Grenoble/CNRS/Université Joseph Fourier, 17 Avenue des Martyrs, 38054, Grenoble Cedex 9, France
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Lucchetti-Miganeh C, Goudenège D, Thybert D, Salbert G, Barloy-Hubler F. SORGOdb: Superoxide Reductase Gene Ontology curated DataBase. BMC Microbiol 2011; 11:105. [PMID: 21575179 PMCID: PMC3116461 DOI: 10.1186/1471-2180-11-105] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 05/16/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Superoxide reductases (SOR) catalyse the reduction of superoxide anions to hydrogen peroxide and are involved in the oxidative stress defences of anaerobic and facultative anaerobic organisms. Genes encoding SOR were discovered recently and suffer from annotation problems. These genes, named sor, are short and the transfer of annotations from previously characterized neelaredoxin, desulfoferrodoxin, superoxide reductase and rubredoxin oxidase has been heterogeneous. Consequently, many sor remain anonymous or mis-annotated. DESCRIPTION SORGOdb is an exhaustive database of SOR that proposes a new classification based on domain architecture. SORGOdb supplies a simple user-friendly web-based database for retrieving and exploring relevant information about the proposed SOR families. The database can be queried using an organism name, a locus tag or phylogenetic criteria, and also offers sequence similarity searches using BlastP. Genes encoding SOR have been re-annotated in all available genome sequences (prokaryotic and eukaryotic (complete and in draft) genomes, updated in May 2010). CONCLUSIONS SORGOdb contains 325 non-redundant and curated SOR, from 274 organisms. It proposes a new classification of SOR into seven different classes and allows biologists to explore and analyze sor in order to establish correlations between the class of SOR and organism phenotypes. SORGOdb is freely available at http://sorgo.genouest.org/index.php.
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Affiliation(s)
- Céline Lucchetti-Miganeh
- CNRS UMR 6026, ICM, Equipe Sp@rte, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, France.
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12
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Pinto AF, Rodrigues JV, Teixeira M. Reductive elimination of superoxide: Structure and mechanism of superoxide reductases. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1804:285-97. [PMID: 19857607 DOI: 10.1016/j.bbapap.2009.10.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Revised: 10/12/2009] [Accepted: 10/14/2009] [Indexed: 10/20/2022]
Abstract
Superoxide anion is among the deleterious reactive oxygen species, towards which all organisms have specialized detoxifying enzymes. For quite a long time, superoxide elimination was thought to occur through its dismutation, catalyzed by Fe, Cu, and Mn or, as more recently discovered, by Ni-containing enzymes. However, during the last decade, a novel type of enzyme was established that eliminates superoxide through its reduction: the superoxide reductases, which are spread among anaerobic and facultative microorganisms, from the three life kingdoms. These enzymes share the same unique catalytic site, an iron ion bound to four histidines and a cysteine that, in its reduced form, reacts with superoxide anion with a diffusion-limited second order rate constant of approximately 10(9) M(-1) s(-1). In this review, the properties of these enzymes will be thoroughly discussed.
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Affiliation(s)
- Ana Filipa Pinto
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida da República (EAN), 2780-157 Oeiras, Portugal
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13
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Brioukhanov AL. Nonheme iron proteins as an alternative system of antioxidant defense in the cells of strictly anaerobic microorganisms: A review. APPL BIOCHEM MICRO+ 2008. [DOI: 10.1134/s0003683808040017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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14
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Zhu J, Fu X, Koo YD, Zhu JK, Jenney FE, Adams MWW, Zhu Y, Shi H, Yun DJ, Hasegawa PM, Bressan RA. An enhancer mutant of Arabidopsis salt overly sensitive 3 mediates both ion homeostasis and the oxidative stress response. Mol Cell Biol 2007; 27:5214-24. [PMID: 17485445 PMCID: PMC1951954 DOI: 10.1128/mcb.01989-06] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Revised: 12/20/2006] [Accepted: 04/04/2007] [Indexed: 11/20/2022] Open
Abstract
The myristoylated calcium sensor SOS3 and its interacting protein kinase, SOS2, play critical regulatory roles in salt tolerance. Mutations in either of these proteins render Arabidopsis thaliana plants hypersensitive to salt stress. We report here the isolation and characterization of a mutant called enh1-1 that enhances the salt sensitivity of sos3-1 and also causes increased salt sensitivity by itself. ENH1 encodes a chloroplast-localized protein with a PDZ domain at the N-terminal region and a rubredoxin domain in the C-terminal part. Rubredoxins are known to be involved in the reduction of superoxide in some anaerobic bacteria. The enh1-1 mutation causes enhanced accumulation of reactive oxygen species (ROS), particularly under salt stress. ROS also accumulate to higher levels in sos2-1 but not in sos3-1 mutants. The enh1-1 mutation does not enhance sos2-1 phenotypes. Also, enh1-1 and sos2-1 mutants, but not sos3-1 mutants, show increased sensitivity to oxidative stress. These results indicate that ENH1 functions in the detoxification of reactive oxygen species resulting from salt stress by participating in a new salt tolerance pathway that may involve SOS2 but not SOS3.
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Affiliation(s)
- Jianhua Zhu
- Horticulture and Landscape Architecture Department, Purdue University, West Lafayette, IN 47907, USA
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15
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Desrosiers DC, Sun YC, Zaidi AA, Eggers CH, Cox DL, Radolf JD. The general transition metal (Tro) and Zn2+(Znu) transporters inTreponema pallidum: analysis of metal specificities and expression profiles. Mol Microbiol 2007; 65:137-52. [PMID: 17581125 DOI: 10.1111/j.1365-2958.2007.05771.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Acquisition of transition metals is central to the struggle between a bacterial pathogen and its mammalian host. Previous studies demonstrated that Treponema pallidum encodes a cluster-9 (C9) ABC transporter (troABCD) whose solute-binding protein component (TroA) ligands Zn(2+) and Mn(2+) with essentially equal affinities. Bioinformatic analysis revealed that T. pallidum encodes an additional C9 transporter (tp0034-36) orthologous to Zn(2+)-uptake (Znu) systems in other bacteria; the binding protein component, ZnuA, contains a His-rich tract characteristic of C9 Zn(2+)-binding proteins. Metal analysis and metal-reconstitution studies demonstrated that ZnuA is a Zn(2+)-binding protein; parallel studies confirmed that TroA binds Zn(2+), Mn(2+) and Fe. Circular dichroism showed that ZnuA, but not TroA, undergoes conformational changes in the presence of Zn(2+). Using isothermal titration calorimetry (ITC), we demonstrated that TroA binds Zn(2+) and Mn(2+) with affinities approximately 100-fold greater than those previously reported. ITC analysis revealed that ZnuA contains multiple Zn(2+)-binding sites, two of which are high-affinity and presumed to be located within the binding pocket and His-rich loop. Quantitative reverse transcription polymerase chain reaction of tro and znu transcripts combined with immunoblot analysis of TroA and ZnuA confirmed that both transporters are simultaneously expressed in T. pallidum and that TroA is expressed at much greater levels than ZnuA. Collectively, our findings indicate that T. pallidum procures transition metals via the concerted utilization of its general metal (Tro) and Zn(2+) (Znu) transporters. Sequestration of periplasmic Zn(2+) by ZnuA may free up TroA binding capacity for the importation of Fe and Mn(2+).
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Affiliation(s)
- Daniel C Desrosiers
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030-3715, USA
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16
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Pereira AS, Tavares P, Folgosa F, Almeida RM, Moura I, Moura JJG. Superoxide Reductases. Eur J Inorg Chem 2007. [DOI: 10.1002/ejic.200700008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Alice S. Pereira
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
| | - Pedro Tavares
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
| | - Filipe Folgosa
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
| | - Rui M. Almeida
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
| | - Isabel Moura
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
| | - José J. G. Moura
- Requimte, Centro de Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829‐516 Caparica, Portugal, Fax: +351‐21‐2948550
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17
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Tan ML, Bizzarri AR, Xiao Y, Cannistraro S, Ichiye T, Manzoni C, Cerullo G, Adams MWW, Jenney FE, Cramer SP. Observation of terahertz vibrations in Pyrococcus furiosus rubredoxin via impulsive coherent vibrational spectroscopy and nuclear resonance vibrational spectroscopy – interpretation by molecular mechanics. J Inorg Biochem 2007; 101:375-84. [PMID: 17204331 DOI: 10.1016/j.jinorgbio.2006.09.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Revised: 09/28/2006] [Accepted: 09/29/2006] [Indexed: 10/24/2022]
Abstract
We have used impulsive coherent vibrational spectroscopy (ICVS) to study the Fe(S-Cys)(4) site in oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf). In this experiment, a 15 fs visible laser pulse is used to coherently pump the sample to an excited electronic state, and a second <10 fs pulse is used to probe the change in transmission as a function of the time delay. PfRd was observed to relax to the ground state by a single exponential decay with time constants of approximately 255-275 fs. Superimposed on this relaxation are oscillations caused by coherent excitation of vibrational modes in both excited and ground electronic states. Fourier transformation reveals the frequencies of these modes. The strongest ICV mode with 570 nm excitation is the symmetric Fe-S stretching mode near 310 cm(-1), compared to 313 cm(-1) in the low temperature resonance Raman. If the rubredoxin is pumped at 520 nm, a set of strong bands occurs between 20 and 110 cm(-1). Finally, there is a mode at approximately 500 cm(-1) which is similar to features near 508 cm(-1) in blue Cu proteins that have been attributed to excited state vibrations. Normal mode analysis using 488 protein atoms and 558 waters gave calculated spectra that are in good agreement with previous nuclear resonance vibrational spectra (NRVS) results. The lowest frequency normal modes are identified as collective motions of the entire protein or large segments of polypeptide. Motion in these modes may affect the polar environment of the redox site and thus tune the electron transfer functions in rubredoxins.
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Affiliation(s)
- Ming-Liang Tan
- Department of Applied Science, University of California, Davis, CA 95616, USA
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18
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Deka RK, Brautigam CA, Tomson FL, Lumpkins SB, Tomchick DR, Machius M, Norgard MV. Crystal structure of the Tp34 (TP0971) lipoprotein of treponema pallidum: implications of its metal-bound state and affinity for human lactoferrin. J Biol Chem 2006; 282:5944-58. [PMID: 17192261 DOI: 10.1074/jbc.m610215200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Tp34 (TP0971) membrane lipoprotein of Treponema pallidum, an obligate human pathogen and the agent of syphilis, was previously reported to have lactoferrin binding properties. Given the non-cultivatable nature of T. pallidum, a structure-to-function approach was pursued to clarify further potential relationships between the Tp34 structural and biochemical properties and its propensity to bind human lactoferrin. The crystal structure of a nonacylated, recombinant form of Tp34 (rTp34), solved to a resolution of 1.9A(,) revealed two metaloccupied binding sites within a dimer; the identity of the ion most likely was zinc. Residues from both of the monomers contributed to the interfacial metal-binding sites; a novel feature was that the delta-sulfur of methionine coordinated the zinc ion. Analytical ultracentrifugation showed that, in solution, rTp34 formed a metal-stabilized dimer and that rTp34 bound human lactoferrin with a stoichiometry of 2:1. Isothermal titration calorimetry further revealed that rTp34 bound human lactoferrin at high (submicromolar) affinity. Finally, membrane topology studies revealed that native Tp34 is not located on the outer surface (outer membrane) of T. pallidum but, rather, is periplasmic. How propensity of Tp34 to bind zinc and the iron-sequestering lactoferrin may relate overall to the biology of T. pallidum infection in humans is discussed.
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Affiliation(s)
- Ranjit K Deka
- Departments of Microbiology and Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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Dolla A, Fournier M, Dermoun Z. Oxygen defense in sulfate-reducing bacteria. J Biotechnol 2006; 126:87-100. [PMID: 16713001 DOI: 10.1016/j.jbiotec.2006.03.041] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Revised: 02/27/2006] [Accepted: 03/29/2006] [Indexed: 11/24/2022]
Abstract
Sulfate-reducing bacteria (SRB) are strict anaerobes that are often found in biotopes where oxic conditions can temporarily exist. The bacteria have developed several defense strategies in order to survive exposure to oxygen. These strategies includes peculiar behaviors in the presence of oxygen, like aggregation or aerotaxis, and enzymatic systems dedicated to the reduction and the elimination of oxygen and its reactive species. Sulfate-reducing bacteria, and specially Desulfovibrio species, possess a variety of enzymes acting together to achieve an efficient defense against oxidative stress. The function and occurrence of these enzymatic systems are described.
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Affiliation(s)
- Alain Dolla
- Laboratoire de Bioénergétique et Ingénierie des Protéines, CNRS - 31 chemin Joseph Aiguier, 13402 Marseille cedex 20, France.
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20
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Santos-Silva T, Trincão J, Carvalho AL, Bonifácio C, Auchère F, Raleiras P, Moura I, Moura JJG, Romão MJ. The first crystal structure of class III superoxide reductase from Treponema pallidum. J Biol Inorg Chem 2006; 11:548-58. [PMID: 16791639 DOI: 10.1007/s00775-006-0104-y] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Accepted: 03/20/2006] [Indexed: 12/01/2022]
Abstract
Superoxide reductase (SOR) is a metalloprotein containing a non-heme iron centre, responsible for the scavenging of superoxide radicals in the cell. The crystal structure of Treponema pallidum (Tp) SOR was determined using soft X-rays and synchrotron radiation. Crystals of the oxidized form were obtained using poly(ethylene glycol) and MgCl2 and diffracted beyond 1.55 A resolution. The overall architecture is very similar to that of other known SORs but TpSOR contains an N-terminal domain in which the desulforedoxin-type Fe centre, found in other SORs, is absent. This domain conserves the beta-barrel topology with an overall arrangement very similar to that of other SOR proteins where the centre is present. The absence of the iron ion and its ligands, however, causes a decrease in the cohesion of the domain and some disorder is observed, particularly in the region where the metal would be harboured. The C-terminal domain exhibits the characteristic immunoglobulin-like fold and harbours the Fe(His)4(Cys) active site. The five ligands of the iron centre are well conserved despite some disorder observed for one of the four molecules in the asymmetric unit. The participation of a glutamate as the sixth ligand of some of the iron centres in Pyrococcus furiosus SOR was not observed in TpSOR. A possible explanation is that either X-ray photoreduction occurred or there was a mixture of redox states at the start of data collection. In agreement with earlier proposals, details in the TpSOR structure also suggest that Lys49 might be involved in attraction of superoxide to the active site.
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Affiliation(s)
- Teresa Santos-Silva
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal
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21
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Auchère F, Pauleta SR, Tavares P, Moura I, Moura JJG. Kinetics studies of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and superoxide reductases. J Biol Inorg Chem 2006; 11:433-44. [PMID: 16544159 DOI: 10.1007/s00775-006-0090-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Accepted: 02/03/2006] [Indexed: 10/24/2022]
Abstract
In this work we present a kinetic study of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and members of the three different classes of superoxide reductases (SORs). SORs from the sulfate-reducing bacteria Desulfovibrio vulgaris (Dv) and D. gigas (Dg) were chosen as prototypes of classes I and II, respectively, while SOR from the syphilis spirochete Treponema pallidum (Tp) was representative of class III. Our results show evidence for different behaviors of SORs toward electron acceptance, with a trend to specificity for the electron donor and acceptor from the same organism. Comparison of the different kapp values, 176.9+/-25.0 min(-1) in the case of the Tp/Tp electron transfer, 31.8+/-3.6 min(-1) for the Dg/Dg electron transfer, and 6.9+/-1.3 min(-1) for Dv/Dv, could suggest an adaptation of the superoxide-mediated electron transfer efficiency to various environmental conditions. We also demonstrate that, in Dg, another iron-sulfur protein, a desulforedoxin, is able to transfer electrons to SOR more efficiently than rubredoxin, with a kapp value of 108.8+/-12.0 min(-1), and was then assigned as the potential physiological electron donor in this organism.
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Affiliation(s)
- Françoise Auchère
- REQUIMTE-Centro de Química Fina e Biotecnologia, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal
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22
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Rodrigues JV, Abreu IA, Saraiva LM, Teixeira M. Rubredoxin acts as an electron donor for neelaredoxin in Archaeoglobus fulgidus. Biochem Biophys Res Commun 2005; 329:1300-5. [PMID: 15766568 DOI: 10.1016/j.bbrc.2005.02.114] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Indexed: 11/19/2022]
Abstract
Archaeoglobus fulgidus neelaredoxin (Nlr) is an electron donor:superoxide oxidoreductase. The reaction of superoxide with reduced Nlr is almost diffusion-limited, but the overall efficiency for detoxifying superoxide in vivo depends on the rate of reduction of Nlr by electron donors. Here, we report the purification and characterization of the two type I rubredoxins from A. fulgidus (AF0880 and AF1349) and show that they act as efficient electron donors for neelaredoxin, in vitro, with a second-order rate constant of 10(7)M(-1)s(-1) at 10 degrees C and pH 7.2.
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Affiliation(s)
- João V Rodrigues
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República (EAN) Apt 127, 2781-901 Oeiras, Portugal
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Colabroy KL, Zhai H, Li T, Ge Y, Zhang Y, Liu A, Ealick SE, McLafferty FW, Begley TP. The Mechanism of Inactivation of 3-Hydroxyanthranilate-3,4-dioxygenase by 4-Chloro-3-hydroxyanthranilate. Biochemistry 2005; 44:7623-31. [PMID: 15909977 DOI: 10.1021/bi0473455] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
3-Hydroxyanthranilate-3,4-dioxygenase (HAD) is a non-heme Fe(II) dependent enzyme that catalyzes the oxidative ring-opening of 3-hydroxyanthranilate to 2-amino-3-carboxymuconic semialdehyde. The enzymatic product subsequently cyclizes to quinolinate, an intermediate in the biosynthesis of nicotinamide adenine dinucleotide. Quinolinate has also been implicated in important neurological disorders. Here, we describe the mechanism by which 4-chloro-3-hydroxyanthranilate inhibits the HAD catalyzed reaction. Using overexpressed and purified bacterial HAD, we demonstrate that 4-chloro-3-hydroxyanthranilate functions as a mechanism-based inactivating agent. The inactivation results in the consumption of 2 +/- 0.8 equiv of oxygen and the production of superoxide. EPR analysis of the inactivation reaction demonstrated that the inhibitor stimulated the oxidation of the active site Fe(II) to the catalytically inactive Fe(III) oxidation state. The inactivated enzyme can be reactivated by treatment with DTT and Fe(II). High resolution ESI-FTMS analysis of the inactivated enzyme demonstrated that the inhibitor did not form an adduct with the enzyme and that four conserved cysteines were oxidized to two disulfides (Cys125-Cys128 and Cys162-Cys165) during the inactivation reaction. These results are consistent with a mechanism in which the enzyme, complexed to the inhibitor and O2, generates superoxide which subsequently dissociates, leaving the inhibitor and the oxidized iron center at the active site.
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Affiliation(s)
- Keri L Colabroy
- Department of Chemistry and Chemical Biology, 120 Baker Laboratory, Cornell University, Ithaca, New York 14853, USA
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