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Çelen Ş, Eğlence-Bakır S, Şahin M, Deniz I, Celik H, Kizilcikli I. Synthesis and characterization of new thiosemicarbazonato molybdenum(VI) complexes and their in vitro antimicrobial activities. J COORD CHEM 2019. [DOI: 10.1080/00958972.2019.1612056] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Şenol Çelen
- Faculty of Engineering, Department of Inorganic Chemistry, Istanbul University-Cerrahpaşa, Istanbul, Turkey
| | - Songül Eğlence-Bakır
- Faculty of Engineering, Department of Inorganic Chemistry, Istanbul University-Cerrahpaşa, Istanbul, Turkey
| | - Musa Şahin
- Faculty of Science, Department of Chemistry, Istanbul University, Istanbul, Turkey
| | - Inci Deniz
- Faculty of Pharmacy, Department of Analytical Chemistry, Yeditepe University, Istanbul, Turkey
| | - Hayati Celik
- Faculty of Pharmacy, Department of Analytical Chemistry, Yeditepe University, Istanbul, Turkey
| | - Irfan Kizilcikli
- Faculty of Engineering, Department of Inorganic Chemistry, Istanbul University-Cerrahpaşa, Istanbul, Turkey
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2
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Eğlence S, Şahin M, Özyürek M, Apak R, Ülküseven B. Dioxomolybdenum(VI) complexes of S-methyl-5-bromosalicylidene-N-alkyl substituted thiosemicarbazones: Synthesis, catalase inhibition and antioxidant activities. Inorganica Chim Acta 2018. [DOI: 10.1016/j.ica.2017.10.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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3
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Hsiao JC, McGrath AP, Kielmann L, Kalimuthu P, Darain F, Bernhardt PV, Harmer J, Lee M, Meyers K, Maher MJ, Kappler U. The central active site arginine in sulfite oxidizing enzymes alters kinetic properties by controlling electron transfer and redox interactions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1859:19-27. [PMID: 28986298 DOI: 10.1016/j.bbabio.2017.10.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 09/29/2017] [Accepted: 10/02/2017] [Indexed: 10/18/2022]
Abstract
A central conserved arginine, first identified as a clinical mutation leading to sulfite oxidase deficiency, is essential for catalytic competency of sulfite oxidizing molybdoenzymes, but the molecular basis for its effects on turnover and substrate affinity have not been fully elucidated. We have used a bacterial sulfite dehydrogenase, SorT, which lacks an internal heme group, but transfers electrons to an external, electron accepting cytochrome, SorU, to investigate the molecular functions of this arginine residue (Arg78). Assay of the SorT Mo centre catalytic competency in the absence of SorU showed that substitutions in the central arginine (R78Q, R78K and R78M mutations) only moderately altered SorT catalytic properties, except for R78M which caused significant reduction in SorT activity. The substitutions also altered the Mo-centre redox potentials (MoVI/V potential lowered by ca. 60-80mV). However, all Arg78 mutations significantly impaired the ability of SorT to transfer electrons to SorU, where activities were reduced 17 to 46-fold compared to SorTWT, precluding determination of kinetic parameters. This was accompanied by the observation of conformational changes in both the introduced Gln and Lys residues in the crystal structure of the enzymes. Taking into account data collected by others on related SOE mutations we propose that the formation and maintenance of an electron transfer complex between the Mo centre and electron accepting heme groups is the main function of the central arginine, and that the reduced turnover and increases in KMsulfite are caused by the inefficient operation of the oxidative half reaction of the catalytic cycle in enzymes carrying these mutations.
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Affiliation(s)
- Ju-Chun Hsiao
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Aaron P McGrath
- Structural Biology Program, Centenary Institute, Locked Bag 6, NSW 2042, Australia
| | - Linda Kielmann
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Palraj Kalimuthu
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Farzana Darain
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Paul V Bernhardt
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Jeffrey Harmer
- Centre for Advanced Imaging, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Mihwa Lee
- Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Kimberley Meyers
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia
| | - Megan J Maher
- Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia.
| | - Ulrike Kappler
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, QLD 4072, Australia.
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Asgharpour Z, Farzaneh F, Ghiasi M, Azarkish M. Synthesis, characterization, density functional theory studies and antibacterial activity of a new Schiff base dioxomolybdenum(VI) complex with tryptophan as epoxidation catalyst. Appl Organomet Chem 2017. [DOI: 10.1002/aoc.3782] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Zeinab Asgharpour
- Department of Chemistry, Faculty of Physics and ChemistryAlzahra University PO Box 1993891176, Vanak Tehran Iran
| | - Faezeh Farzaneh
- Department of Chemistry, Faculty of Physics and ChemistryAlzahra University PO Box 1993891176, Vanak Tehran Iran
| | - Mina Ghiasi
- Department of Chemistry, Faculty of Physics and ChemistryAlzahra University PO Box 1993891176, Vanak Tehran Iran
| | - Mohammad Azarkish
- Department of ChemistryPayame Noor University (PNU) 19395‐4697 Tehran Iran
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5
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Maia LB, Moura I, Moura JJ. EPR Spectroscopy on Mononuclear Molybdenum-Containing Enzymes. FUTURE DIRECTIONS IN METALLOPROTEIN AND METALLOENZYME RESEARCH 2017. [DOI: 10.1007/978-3-319-59100-1_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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6
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Synthesis, crystal structure and DFT studies of a new dioxomolybdenum(VI) Schiff base complex as an olefin epoxidation catalyst. Polyhedron 2015. [DOI: 10.1016/j.poly.2015.09.030] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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7
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Takjoo R, Akbari A, Ahmadi M, Amiri Rudbari H, Bruno G. Synthesis, spectroscopy, DFT and crystal structure investigations of 3-methoxy-2-hydroxybenzaldehyde S-ethylisothiosemicarbazone and its Ni(II) and Mo(VI) complexes. Polyhedron 2013. [DOI: 10.1016/j.poly.2013.02.078] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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8
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Klein EL, Astashkin AV, Raitsimring AM, Enemark JH. Applications of pulsed EPR spectroscopy to structural studies of sulfite oxidizing enzymes(). Coord Chem Rev 2013; 257:110-118. [PMID: 23440026 DOI: 10.1016/j.ccr.2012.05.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Sulfite oxidizing enzymes (SOEs), including sulfite oxidase (SO) and bacterial sulfite dehydrogenase (SDH), catalyze the oxidation of sulfite (SO(3) (2-)) to sulfate (SO(4) (2-)). The active sites of SO and SDH are nearly identical, each having a 5-coordinate, pseudo-square-pyramidal Mo with an axial oxo ligand and three equatorial sulfur donor atoms. One sulfur is from a conserved Cys residue and two are from a pyranopterindithiolene (molybdopterin, MPT) cofactor. The identity of the remaining equatorial ligand, which is solvent-exposed, varies during the catalytic cycle. Numerous in vitro studies, particularly those involving electron paramagnetic resonance (EPR) spectroscopy of the Mo(V) states of SOEs, have shown that the identity and orientation of this exchangeable equatorial ligand depends on the buffer pH, the presence and concentration of certain anions in the buffer, as well as specific point mutations in the protein. Until very recently, however, EPR has not been a practical technique for directly probing specific structures in which the solvent-exposed, exchangeable ligand is an O, OH(-), H(2)O, SO(3) (2-), or SO(4) (2-) group, because the primary O and S isotopes ((16)O and (32)S) are magnetically silent (I = 0). This review focuses on the recent advances in the use of isotopic labeling, variable-frequency high resolution pulsed EPR spectroscopy, synthetic model compounds, and DFT calculations to elucidate the roles of various anions, point mutations, and steric factors in the formation, stabilization, and transformation of SOE active site structures.
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Affiliation(s)
- Eric L Klein
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721-0041, USA
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Qiu JA, Wilson HL, Rajagopalan KV. Structure-based alteration of substrate specificity and catalytic activity of sulfite oxidase from sulfite oxidation to nitrate reduction. Biochemistry 2012; 51:1134-47. [PMID: 22263579 DOI: 10.1021/bi201206v] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Eukaryotic sulfite oxidase is a dimeric protein that contains the molybdenum cofactor and catalyzes the metabolically essential conversion of sulfite to sulfate as the terminal step in the metabolism of cysteine and methionine. Nitrate reductase is an evolutionarily related molybdoprotein in lower organisms that is essential for growth on nitrate. In this study, we describe human and chicken sulfite oxidase variants in which the active site has been modified to alter substrate specificity and activity from sulfite oxidation to nitrate reduction. On the basis of sequence alignments and the known crystal structure of chicken sulfite oxidase, two residues are conserved in nitrate reductases that align with residues in the active site of sulfite oxidase. On the basis of the crystal structure of yeast nitrate reductase, both positions were mutated in human sulfite oxidase and chicken sulfite oxidase. The resulting double-mutant variants demonstrated a marked decrease in sulfite oxidase activity but gained nitrate reductase activity. An additional methionine residue in the active site was proposed to be important in nitrate catalysis, and therefore, the triple variant was also produced. The nitrate reducing ability of the human sulfite oxidase triple mutant was nearly 3-fold greater than that of the double mutant. To obtain detailed structural data for the active site of these variants, we introduced the analogous mutations into chicken sulfite oxidase to perform crystallographic analysis. The crystal structures of the Mo domains of the double and triple mutants were determined to 2.4 and 2.1 Å resolution, respectively.
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Affiliation(s)
- James A Qiu
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, United States
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Klein EL, Raitsimring AM, Astashkin AV, Rajapakshe A, Johnson-Winters K, Arnold AR, Potapov A, Goldfarb D, Enemark JH. Identity of the exchangeable sulfur-containing ligand at the Mo(V) center of R160Q human sulfite oxidase. Inorg Chem 2012; 51:1408-18. [PMID: 22225516 DOI: 10.1021/ic201643t] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In our previous study of the fatal R160Q mutant of human sulfite oxidase (hSO) at low pH (Astashkin et al. J. Am. Chem. Soc.2008, 130, 8471-8480), a new Mo(V) species, denoted "species 1", was observed at low pH values. Species 1 was ascribed to a six-coordinate Mo(V) center with an exchangeable terminal oxo ligand and an equatorial sulfate group on the basis of pulsed EPR spectroscopy and (33)S and (17)O labeling. Here we report new results for species 1 of R160Q, based on substitution of the sulfur-containing ligand by a phosphate group, pulsed EPR spectroscopy in K(a)- and W-bands, and extensive density functional theory (DFT) calculations applied to large, more realistic molecular models of the enzyme active site. The combined results unambiguously show that species 1 has an equatorial sulfite as the only exchangeable ligand. The two types of (17)O signals that are observed arise from the coordinated and remote oxygen atoms of the sulfite ligand. A typical five-coordinate Mo(V) site is compatible with the observed and calculated EPR parameters.
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Affiliation(s)
- Eric L Klein
- Department of Chemistry and Biochemistry, 1306 East University Boulevard, University of Arizona, Tucson, Arizona 85721-0041, United States
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11
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Samuel PP, Horn S, Döring A, Havelius KGV, Reschke S, Leimkühler S, Haumann M, Schulzke C. A Crystallographic and Mo K-Edge XAS Study of Molybdenum Oxo Bis-, Mono-, and Non-Dithiolene Complexes - First-Sphere Coordination Geometry and Noninnocence of Ligands. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201100331] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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12
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Magalon A, Fedor JG, Walburger A, Weiner JH. Molybdenum enzymes in bacteria and their maturation. Coord Chem Rev 2011. [DOI: 10.1016/j.ccr.2010.12.031] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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Enemark JH, Raitsimring AM, Astashkin AV, Klein EL. Implications for the mechanism of sulfite oxidizing enzymes from pulsed EPR spectroscopy and DFT calculations for "difficult" nuclei. Faraday Discuss 2011; 148:249-67; discussion 299-314. [PMID: 21322488 PMCID: PMC3079391 DOI: 10.1039/c004404k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The catalytic mechanisms of sulfite oxidizing enzymes (SOEs) have been investigated by multi-frequency pulsed EPR measurements of "difficult" magnetic nuclei (35.37Cl, 33S, 17O) associated with the Mo(v) center. Extensive DFT calculations have been used to relate the experimental magnetic resonance parameters of these nuclei to specific active site structures. This combined spectroscopic and computational approach has provided new insights concerning the structure/function relationships of the active sites of SOEs, including: (i) the exchange of oxo ligands; (ii) the nature of the blocked forms; and (iii) the role of Cl- in low pH forms.
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Affiliation(s)
- John H Enemark
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721-0041, USA.
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15
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Pushie MJ, Doonan CJ, Moquin K, Weiner JH, Rothery R, George GN. Molybdenum Site Structure of Escherichia coli YedY, a Novel Bacterial Oxidoreductase. Inorg Chem 2010; 50:732-40. [DOI: 10.1021/ic101280m] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. Jake Pushie
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Christian J. Doonan
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Kamila Moquin
- School of Molecular and Systems Medicine, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Joel H. Weiner
- School of Molecular and Systems Medicine, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Richard Rothery
- School of Molecular and Systems Medicine, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Graham N. George
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
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Rajapakshe A, Johnson-Winters K, Nordstrom AR, Meyers KT, Emesh S, Astashkin AV, Enemark JH. Characterization of chloride-depleted human sulfite oxidase by electron paramagnetic resonance spectroscopy: experimental evidence for the role of anions in product release. Biochemistry 2010; 49:5154-9. [PMID: 20491442 DOI: 10.1021/bi902172n] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Mo(V) state of the molybdoenzyme sulfite oxidase (SO) is paramagnetic and can be studied by electron paramagnetic resonance (EPR) spectroscopy. Vertebrate SO at pH <7 and >9 exhibits characteristic EPR spectra that correspond to two structurally different forms of the Mo(V) active center termed the low-pH (lpH) and high-pH (hpH) forms, respectively. Both EPR forms have an exchangeable equatorial OH ligand, but its orientation in the two forms is different. It has been hypothesized that the formation of the lpH species is dependent on the presence of chloride. In this work, we have prepared and purified samples of the wild type and various mutants of human SO that are depleted of chloride. These samples do not exhibit the typical lpH EPR spectrum at low pH but rather exhibit spectra that are characteristic of the blocked species that contains an exchangeable equatorial sulfate ligand. Addition of chloride to these samples results in the disappearance of the blocked species and the formation of the lpH species. Similarly, if chloride is added before sulfite, the lpH species is formed instead of the blocked one. Qualitatively similar results were observed for samples of sulfite-oxidizing enzymes from other organisms that were previously reported to form a blocked species at low pH. However, the depletion of chloride has no effect upon the formation of the hpH species.
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Affiliation(s)
- Asha Rajapakshe
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA
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Pushie MJ, George GN. Active-site dynamics and large-scale domain motions of sulfite oxidase: a molecular dynamics study. J Phys Chem B 2010; 114:3266-75. [PMID: 20158265 DOI: 10.1021/jp908731f] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The physiologically vital enzyme sulfite oxidase employs rapid intramolecular electron transfer between a molybdenum ion in the C-terminal domain (the site of sulfite oxidation) and a heme moeity in the N-terminal domain to complete its catalytic cycle. Crystal structures of the enzyme show C- and N-terminal domain orientations that are not consistent with rapid intramolecular electron transfer. Domain motion has been postulated to explain this discrepancy. In the present work we employ molecular dynamics simulations to understand the large-scale domain motions of the enzyme. We observe motion of the N-terminal domain into an orientation similar to that postulated for rapid electron transfer. Our simulations also probe the dynamics of the active site and surrounding residues, adding a further level of structural and thermodynamic detail in understanding sulfite oxidase function.
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Affiliation(s)
- M Jake Pushie
- Molecular and Environmental Science Research Group, Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada
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18
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Rapson TD, Astashkin AV, Johnson-Winters K, Bernhardt PV, Kappler U, Raitsimring AM, Enemark JH. Pulsed EPR investigations of the Mo(V) centers of the R55Q and R55M variants of sulfite dehydrogenase from Starkeya novella. J Biol Inorg Chem 2010; 15:505-14. [PMID: 20084533 DOI: 10.1007/s00775-009-0619-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 12/13/2009] [Indexed: 10/20/2022]
Abstract
Continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy have been used to characterize two variants of bacterial sulfite dehydrogenase (SDH) from Starkeya novella in which the conserved active-site arginine residue (R55) is replaced by a neutral amino acid residue. Substitution by the hydrophobic methionine residue (SDH(R55M)) has essentially no effect on the pH dependence of the EPR properties of the Mo(V) center, even though the X-ray structure of this variant shows that the methionine residue is rotated away from the Mo center and a sulfate anion is present in the active-site pocket (Bailey et al. in J Biol Chem 284:2053-2063, 2009). For SDH(R55M) only the high-pH form is observed, and samples prepared in H(2)(17)O-enriched buffer show essentially the same (17)O hyperfine interaction and nuclear quadrupole interaction parameters as SDH(WT) enzyme. However, the pH dependence of the EPR spectra of SDH(R55Q), in which the positively charged arginine is replaced by the neutral hydrophilic glutamine, differs significantly from that of SDH(WT). For SDH(R55Q) the blocked form with bound sulfate is generated at low pH, as verified by (33)S couplings observed upon reduction with (33)S-labeled sulfite. This observation of bound sulfate for SDH(R55Q) supports our previous hypothesis that sulfite-oxidizing enzymes can exhibit multiple pathways for electron transfer and product release (Emesh et al. in Biochemistry 48:2156-2163, 2009). At pH > or = 8 the high-pH form dominates for SDH(R55Q).
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Affiliation(s)
- Trevor D Rapson
- Centre for Metals in Biology, School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QLD, 4072, Australia
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HIGH-RESOLUTION EPR SPECTROSCOPY OF MO ENZYMES. SULFITE OXIDASES: STRUCTURAL AND FUNCTIONAL IMPLICATIONS. BIOLOGICAL MAGNETIC RESONANCE 2010; 29:121-168. [PMID: 21283528 PMCID: PMC3030814 DOI: 10.1007/978-1-4419-1139-1_6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Sulfite oxidases (SOs) are physiologically vital Mo-containing enzymes that occur in animals, plants, and bacteria and which catalyze the oxidation of sulfite to sulfate, the terminal reaction in the oxidative degradation of sulfur-containing compounds. X-ray structure determinations of SOs from several species show nearly identical coordination structures of the molybdenum active center, and a common catalytic mechanism has been proposed that involves the generation of a transient paramagnetic Mo(V) state through a series of coupled electron-proton transfer steps. This chapter describes the use of pulsed electron-nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopic techniques to obtain information about the structure of this Mo(V) species from the hyperfine interactions (hfi) and nuclear quadrupole interactions (nqi) of nearby magnetic nuclei. Variable frequency instrumentation is essential to optimize the experimental conditions for measuring the couplings of different types of nuclei (e.g., (1)H, (2)H, (31)P, and (17)O). The theoretical background necessary for understanding the ESEEM and ENDOR spectra of the Mo(V) centers of SOs is outlined, and examples of the use of advanced pulsed EPR methods (RP-ESEEM, HYSCORE, integrated four-pulse ESEEM) for structure determination are presented. The analysis of variable-frequency pulsed EPR data from SOs is aided by parallel studies of model compounds that contain key functional groups or that are isotopically labeled and thus provide benchmark data for enzymes. Enormous progress has been made on the use of high-resolution variable-frequency pulsed EPR methods to investigate the structures and mechanisms of SOs during the past ~15 years, and the future is bright for the continued development and application of this technology to SOs, other molybdenum enzymes, and other problems in metallobiochemistry.
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Klein EL, Astashkin AV, Ganyushin D, Riplinger C, Johnson-Winters K, Neese F, Enemark JH. Direct detection and characterization of chloride in the active site of the low-pH form of sulfite oxidase using electron spin echo envelope modulation spectroscopy, isotopic labeling, and density functional theory calculations. Inorg Chem 2009; 48:4743-52. [PMID: 19402624 DOI: 10.1021/ic801787s] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electron spin echo envelope modulation (ESEEM) investigations were carried out on samples of the low-pH (lpH) form of vertebrate sulfite oxidase (SO) prepared with (35)Cl- and (37)Cl-enriched buffers, as well as with buffer containing the natural abundance of Cl isotopes. The isotope-related changes observed in the ESEEM spectra provide direct and unequivocal evidence that Cl(-) is located in close proximity to the Mo(V) center of lpH SO. The measured isotropic hyperfine interaction constant of about 4 MHz ((35)Cl) suggests that the Cl(-) ion is either weakly coordinated to Mo(V) at its otherwise vacant axial position, trans to the oxo ligand, or is hydrogen-bonded to the equatorial exchangeable OH ligand. Scalar relativistic all-electron density functional theory (DFT) calculations of the hyperfine and nuclear quadrupole interaction parameters, along with steric and energetic arguments, strongly support the possibility that Cl(-) is hydrogen-bonded to the equatorial OH ligand rather than being directly coordinated to the Mo(V).
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Affiliation(s)
- Eric L Klein
- Department of Chemistry and Biochemistry, University of Arizona, 1306 E. University Boulevard, Tucson, Arizona 85721, USA
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Structures and reaction pathways of the molybdenum centres of sulfite-oxidizing enzymes by pulsed EPR spectroscopy. Biochem Soc Trans 2009; 36:1129-33. [PMID: 19021510 DOI: 10.1042/bst0361129] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
SOEs (sulfite-oxidizing enzymes) are physiologically vital and occur in all forms of life. During the catalytic cycle, the five-co-ordinate square pyramidal oxo-molybdenum active site passes through the Mo(V) state, and intimate details of the structure can be obtained from variable frequency pulsed EPR spectroscopy through the hyperfine and nuclear quadrupole interactions of nearby magnetic nuclei. By employing variable spectrometer operational frequencies, it is possible to optimize the measurement conditions for difficult quadrupolar nuclei of interest (e.g. (17)O, (33)S, (35)Cl and (37)Cl) and to simplify the interpretation of the spectra. Isotopically labelled model Mo(V) compounds provide further insight into the electronic and geometric structures and chemical reactions of the enzymes. Recently, blocked forms of SOEs having co-ordinated sulfate, the reaction product, were detected using (33)S (I=3/2) labelling. This blocking of product release is a possible contributor to fatal human sulfite oxidase deficiency in young children.
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George SJ, Drury OB, Fu J, Friedrich S, Doonan CJ, George GN, White JM, Young CG, Cramer SP. Molybdenum X-ray absorption edges from 200 to 20,000eV: the benefits of soft X-ray spectroscopy for chemical speciation. J Inorg Biochem 2008; 103:157-67. [PMID: 19041140 DOI: 10.1016/j.jinorgbio.2008.09.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 09/16/2008] [Accepted: 09/18/2008] [Indexed: 11/25/2022]
Abstract
We have surveyed the chemical utility of the near-edge structure of molybdenum X-ray absorption edges from the hard X-ray K-edge at 20,000eV down to the soft X-ray M(4,5)-edges at approximately 230eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO(4)(2-) and MoS(4)(2-). We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO(4)(2-) and MoS(4)(2-) and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L(2,3)-edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft X-ray M(2,3)-edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L(2,3)-edges. Interestingly, the soft X-ray, low energy ( approximately 230eV) M(4,5)-edges had greatest potential chemical sensitivity and using our high-resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d-->5p transitions, while the broad edge structure has predominately 3d-->4f character. A proper understanding of the dependence of these soft X-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M(4,5)-edges can be made. This work includes crystallographic characterization of sodium tetrathiomolybdate.
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Affiliation(s)
- Simon J George
- Advanced Biological and Environmental X-ray Facility, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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Evolutionary persistence of the molybdopyranopterin-containing sulfite oxidase protein fold. Microbiol Mol Biol Rev 2008; 72:228-48, table of contents. [PMID: 18535145 DOI: 10.1128/mmbr.00041-07] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SUMMARY The importance of molybdoenzymes is exemplified both by the debilitating and fatal human diseases caused by their deficiency and by their persistence throughout evolution. Here, we show that the protein fold of the molybdopyranopterin-containing domain of sulfite oxidase (the SUOX fold) can be found in all three domains of life. Analyses of sequence data and protein structure comparisons (secondary structure matching) show that the SUOX fold is found in enzymes that have quite distinct macromolecular architectures comprising one or more domains and sometimes subsidiary subunits. These are summarized as follows: (i) animal SUOXs that contain an N-terminal cytochrome b(5) domain and an SUOX fold fused to a C-terminal dimerization domain; (ii) plant SUOX that contains an SUOX fold fused to a C-terminal dimerization domain; (iii) the YedY protein from Escherichia coli, which comprises only the SUOX fold; (iv) the sulfite dehydrogenase from Starkeya novella that contains the SUOX fold, a dimerization domain, and an additional c-type cytochrome subunit; and (v) the plant-type nitrate reductases, exemplified by that of Pichia angusta, that contain an N-terminal SUOX fold, a dimerization domain, a cytochrome b(5) domain, and a C-terminal NADH binding flavin adenine dinucleotide-containing domain. We used the primary sequences of the proteins containing an SUOX fold to mine 559 sequences of related proteins. A phylogeny of a nonredundant subset of these sequences was generated, and the resultant clades were categorized by sequence motif analyses in the context of the available protein structures. Based on the motif analyses, cladistics, and domain conservations, we are able to postulate a plausible pathway of SUOX fold enzyme evolution.
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Astashkin AV, Johnson-Winters K, Klein EL, Feng C, Wilson HL, Rajagopalan KV, Raitsimring AM, Enemark JH. Structural studies of the molybdenum center of the pathogenic R160Q mutant of human sulfite oxidase by pulsed EPR spectroscopy and 17O and 33S labeling. J Am Chem Soc 2008; 130:8471-80. [PMID: 18529001 PMCID: PMC2779766 DOI: 10.1021/ja801406f] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electron paramagnetic resonance (EPR) investigation of the Mo(V) center of the pathogenic R160Q mutant of human sulfite oxidase (hSO) confirms the presence of three distinct species whose relative abundances depend upon pH. Species 1 is exclusively present at pH < or = 6, and remains in significant amounts even at pH 8. Variable-frequency electron spin echo envelope modulation (ESEEM) studies of this species prepared with (33)S-labeled sulfite clearly show the presence of coordinated sulfate, as has previously been found for the "blocked" form of Arabidopsis thaliana at low pH (Astashkin, A. V.; Johnson-Winters, K.; Klein, E. L.; Byrne, R. S.; Hille, R.; Raitsimring, A. M.; Enemark, J. H. J. Am. Chem. Soc. 2007, 129, 14800). The ESEEM spectra of Species 1 prepared in (17)O-enriched water show both strongly and weakly magnetically coupled (17)O atoms that can be assigned to an equatorial sulfate ligand and the axial oxo ligand, respectively. The nuclear quadrupole interaction (nqi) of the axial oxo ligand is substantially stronger than those found for other oxo-Mo(V) centers studied previously. Additionally, pulsed electron-nuclear double resonance (ENDOR) measurements reveal a nearby weakly coupled exchangeable proton. The structure for Species 1 proposed from the pulsed EPR results using isotopic labeling is a six-coordinate Mo(V) center with an equatorial sulfate ligand that is hydrogen bonded to an exchangeable proton. Six-coordination is supported by the (17)O nqi parameters for the axial oxo group of the model compound, (dttd)Mo(17)O((17)Otms), where H2dttd = 2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane; tms = trimethylsilyl. Reduction of R160Q to Mo(V) with Ti(III) gives primarily Species 2, another low pH form, whereas reduction with sulfite at higher pH values gives a mixture of Species 1 and 2, as well as the "primary" high pH form of wild-type SO. The occurrence of significant amounts of the "sulfate-blocked" form of R160Q (Species 1) at physiological pH suggests that this species may be a contributing factor to the lethality of this mutation.
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Affiliation(s)
- Andrei V Astashkin
- Department of Chemistry, 1306 E University Blvd, University of Arizona, Tucson, Arizona 86721-0041, USA
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Doonan CJ, Wilson HL, Bennett B, Prince RC, Rajagopalan KV, George GN. MoV electron paramagnetic resonance of sulfite oxidase revisited: the low-pH chloride signal. Inorg Chem 2008; 47:2033-8. [PMID: 18271529 PMCID: PMC2841525 DOI: 10.1021/ic7017083] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Valuable information on the active sites of molybdenum enzymes has been provided by Mo(V) electron paramagnetic resonance (EPR) spectroscopy. In recent years, multiple resonance techniques have been extensively used to examine details of the active-site structure, but basic continuous-wave (CW) EPR has not been re-evaluated in several decades. Here, we present a re-examination of the CW EPR spectroscopy of the sulfite oxidase low-pH chloride species and provide evidence for direct coordination of molybdenum by chloride.
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Affiliation(s)
- Christian J. Doonan
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Heather L. Wilson
- Department of Biochemistry, School of Medicine, Duke University, Durham, North Carolina 27710
| | - Brian Bennett
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226
| | - Roger C. Prince
- ExxonMobil Biomedical Sciences Inc., Annandale, New Jersey 08801
| | - K. V. Rajagopalan
- Department of Biochemistry, School of Medicine, Duke University, Durham, North Carolina 27710
| | - Graham N. George
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
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