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Sasoni N, Ferrero DML, Guerrero SA, Iglesias AA, Arias DG. First evidence of glutathione metabolism in Leptospira interrogans. Free Radic Biol Med 2019; 143:366-374. [PMID: 31465831 DOI: 10.1016/j.freeradbiomed.2019.08.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 07/08/2019] [Accepted: 08/24/2019] [Indexed: 11/28/2022]
Abstract
BACKGROUND Glutathione (GSH) plays a role as a main antioxidant metabolite in all eukaryotes and many prokaryotes. Most of the organisms synthesize GSH by a pathway involving two enzymatic reactions, each one consuming one molecule of ATP. In a first step mediated by glutamate-cysteine ligase (GCL), the carboxylate of l-glutamic acid reacts with l-cysteine to form the dipeptide γ-glutamylcysteine (γ-GC). The second step involves the addition of glycine to the C-terminal of γ-GC catalyzed by glutathione synthetase (GS). In many bacteria, such as in the pathogen Leptospira interrogans, the main intracellular thiol has not yet been identified and the presence of GSH is not clear. METHODS We performed the molecular cloning of the genes gshA and gshB from L. interrogans; which respectively code for GCL and GS. After heterologous expression of the cloned genes we recombinantly produced the respective proteins with high degree of purity. These enzymes were exhaustively characterized in their biochemical properties. In addition, we determined the contents of GSH and the activity of related enzymes (and proteins) in cell extracts of the bacterium. RESULTS We functionally characterized GCL and GS, the two enzymes putatively involved in GSH synthesis in L. interrogans serovar Copenhageni. LinGCL showed higher substrate promiscuity (was active in presence of l-glutamic acid, l-cysteine and ATP, and also with GTP, l-aspartic acid and l-serine in lower proportion) unlike LinGS (which was only active with γ-GC, l-glycine and ATP). LinGCL is significantly inhibited by γ-GC and GSH, the respective intermediate and final product of the synthetic pathway. GSH showed inhibitory effect over LinGS but with a lower potency than LinGCL. Going further, we detected the presence of GSH in L. interrogans cells grown under basal conditions and also determined enzymatic activity of several GSH-dependent/related proteins in cell extracts. CONCLUSIONS and General Significance. Our results contribute with novel insights concerning redox metabolism in L. interrogans, mainly supporting that GSH is part of the antioxidant defense in the bacterium.
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Affiliation(s)
- Natalia Sasoni
- Instituto de Agrobiotecnología del Litoral (CONICET-UNL), Facultad de Bioquímica y Ciencias Biológicas (FBCB), Centro Científico Tecnológico CONICET Santa Fe, Colectora Ruta Nacional Nº 168 km 0, Santa Fe, 3000, Argentina
| | - Danisa M L Ferrero
- Instituto de Agrobiotecnología del Litoral (CONICET-UNL), Facultad de Bioquímica y Ciencias Biológicas (FBCB), Centro Científico Tecnológico CONICET Santa Fe, Colectora Ruta Nacional Nº 168 km 0, Santa Fe, 3000, Argentina
| | - Sergio A Guerrero
- Instituto de Agrobiotecnología del Litoral (CONICET-UNL), Facultad de Bioquímica y Ciencias Biológicas (FBCB), Centro Científico Tecnológico CONICET Santa Fe, Colectora Ruta Nacional Nº 168 km 0, Santa Fe, 3000, Argentina
| | - Alberto A Iglesias
- Instituto de Agrobiotecnología del Litoral (CONICET-UNL), Facultad de Bioquímica y Ciencias Biológicas (FBCB), Centro Científico Tecnológico CONICET Santa Fe, Colectora Ruta Nacional Nº 168 km 0, Santa Fe, 3000, Argentina
| | - Diego G Arias
- Instituto de Agrobiotecnología del Litoral (CONICET-UNL), Facultad de Bioquímica y Ciencias Biológicas (FBCB), Centro Científico Tecnológico CONICET Santa Fe, Colectora Ruta Nacional Nº 168 km 0, Santa Fe, 3000, Argentina.
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Veltman K, Harris C, Ahmad Y, Jolliet O. A mechanistic model for thiol redox dynamics in the organogenesis stage rat conceptus. Reprod Toxicol 2018; 82:38-49. [PMID: 30292673 PMCID: PMC9999374 DOI: 10.1016/j.reprotox.2018.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 08/07/2018] [Accepted: 09/19/2018] [Indexed: 11/17/2022]
Abstract
Precise control of the glutathione/glutathione disulfide (GSH/GSSG) redox balance is vital for the developing embryo, but regulatory mechanisms are poorly understood. We developed a novel, mechanistic mass-balance model for GSH metabolism in the organogenesis stage (gestational day 10.0-11.13) rat conceptus predicting the dynamics of 8 unique metabolites in 3 conceptal compartments: the visceral yolk sac (VYS), the extra-embryonic fluid (EEF) and the embryo proper (EMB). Our results show that thiol concentrations in all compartments are well predicted by the model. Protein synthesis is predicted to be a major efflux pathway for all amino acid precursors of GSH synthesis and an essential model element. Our model provides quantitative insights in the transport fluxes and enzymatic fluxes needed to maintain thiol redox balances under normal physiological conditions. This is crucial to further elucidate the mechanisms through which chemical exposure can perturb redox homeostasis, causing oxidative stress, and potentially birth defects.
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Affiliation(s)
- K Veltman
- Department of Environmental Health Sciences, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109-2029, USA.
| | - C Harris
- Department of Environmental Health Sciences, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109-2029, USA
| | - Y Ahmad
- Department of Environmental Health Sciences, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109-2029, USA
| | - O Jolliet
- Department of Environmental Health Sciences, University of Michigan, 1420 Washington Heights, Ann Arbor, MI 48109-2029, USA
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3
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Genetic Mutations in the S-loop of Human Glutathione Synthetase: Links Between Substrate Binding, Active Site Structure and Allostery. Comput Struct Biotechnol J 2018; 17:31-38. [PMID: 30581542 PMCID: PMC6297838 DOI: 10.1016/j.csbj.2018.11.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 11/21/2018] [Accepted: 11/23/2018] [Indexed: 12/24/2022] Open
Abstract
The second step in the biosynthesis of the cellular antioxidant glutathione (GSH) is catalyzed by human glutathione synthetase (hGS), a negatively cooperative homodimer. Patients with mutations in hGS have been reported to exhibit a range of symptoms from hemolytic anemia and metabolic acidosis to neurological disorders and premature death. Several patient mutations occur in the S-loop of hGS, a series of residues near the negatively cooperative γ-GC substrate binding site. Experimental point mutations and molecular dynamic simulations show the S-loop not only binds γ-GC through a salt bridge and multiple hydrogen bonds, but the residues also modulate allosteric communication in hGS. By elucidating the role of S-loop residues in active site structure, substrate binding, and allostery, the atomic level sequence of events that leads to the detrimental effects of hGS mutations in patients are more fully understood.
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Key Words
- DSC, differential scanning calorimetry
- Eint, average energy of interaction.
- GSH, glutathione
- IPTG, isopropyl-1-thio-β-galactopyranoside
- LDH, lactate dehydrogenase
- MD, molecular dynamics
- PEP, phosphoenolpyruvic acid
- PK, pyruvate kinase
- Td, denaturation temperature midpoint
- WT, wild-type
- hGS, human glutathione synthetase
- γ-GC, γ-glutamylcysteine
- γ-GluABA, L-γ-glutamyl-L-α-aminobutyrate
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4
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Walker V, Mills GA, Anderson ME, Ingle BL, Jackson JM, Moss CL, Sharrod-Cole H, Skipp PJ. The acetaminophen metabolite N-acetyl-p-benzoquinone imine (NAPQI) inhibits glutathione synthetase in vitro; a clue to the mechanism of 5-oxoprolinuric acidosis? Xenobiotica 2016; 47:164-175. [PMID: 27086508 DOI: 10.3109/00498254.2016.1166533] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
1. Metabolic acidosis due to accumulation of l-5-oxoproline is a rare, poorly understood, disorder associated with acetaminophen treatment in malnourished patients with chronic morbidity. l-5-Oxoprolinuria signals abnormal functioning of the γ-glutamyl cycle, which recycles and synthesises glutathione. Inhibition of glutathione synthetase (GS) by N-acetyl-p-benzoquinone imine (NAPQI) could contribute to 5-oxoprolinuric acidosis in such patients. We investigated the interaction of NAPQI with GS in vitro. 2. Peptide mapping of co-incubated NAPQI and GS using mass spectrometry demonstrated binding of NAPQI with cysteine-422 of GS, which is known to be essential for GS activity. Computational docking shows that NAPQI is properly positioned for covalent bonding with cysteine-422 via Michael addition and hence supports adduct formation. 3. Co-incubation of 0.77 μM of GS with NAPQI (25-400 μM) decreased enzyme activity by 16-89%. Inhibition correlated strongly with the concentration of NAPQI and was irreversible. 4. NAPQI binds covalently to GS causing irreversible enzyme inhibition in vitro. This is an important novel biochemical observation. It is the first indication that NAPQI may inhibit glutathione synthesis, which is pivotal in NAPQI detoxification. Further studies are required to investigate its biological significance and its role in 5-oxoprolinuric acidosis.
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Affiliation(s)
- Valerie Walker
- a Department of Clinical Biochemistry , University Hospital Southampton NHS Foundation Trust , Southampton , UK
| | - Graham A Mills
- b School of Pharmacy and Biomedical Sciences, University of Portsmouth , Portsmouth , UK
| | - Mary E Anderson
- c Department of Chemistry and Biochemistry , Texas Woman's University , Denton , TX , USA
| | - Brandall L Ingle
- d Department of Chemistry , Center for Advanced Scientific Computing and Modeling, University of North Texas , Denton , TX , USA
| | - John M Jackson
- e NIHR Southampton Biomedical Research Centre, Southampton General Hospital , Southampton , UK , and
| | - Charlotte L Moss
- f Centre for Proteomic Research and Biological Sciences, University of Southampton , Southampton , UK
| | - Hayley Sharrod-Cole
- a Department of Clinical Biochemistry , University Hospital Southampton NHS Foundation Trust , Southampton , UK
| | - Paul J Skipp
- f Centre for Proteomic Research and Biological Sciences, University of Southampton , Southampton , UK
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5
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De Jesus MC, Ingle BL, Barakat KA, Shrestha B, Slavens KD, Cundari TR, Anderson ME. The role of strong electrostatic interactions at the dimer interface of human glutathione synthetase. Protein J 2015; 33:403-9. [PMID: 25070563 DOI: 10.1007/s10930-014-9573-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The obligate homodimer human glutathione synthetase (hGS) provides an ideal system for exploring the role of protein-protein interactions in the structural stability, activity and allostery of enzymes. The two active sites of hGS, which are 40 Å apart, display allosteric modulation by the substrate γ-glutamylcysteine (γ-GC) during the synthesis of glutathione, a key cellular antioxidant. The two subunits interact at a relatively small dimer interface dominated by electrostatic interactions between S42, R221, and D24. Alanine scans of these sites result in enzymes with decreased activity, altered γ-GC affinity, and decreased thermal stability. Molecular dynamics simulations indicate these mutations disrupt interchain bonding and impact the tertiary structure of hGS. While the ionic hydrogen bonds and salt bridges between S42, R221, and D24 do not mediate allosteric communication in hGS, these interactions have a dramatic impact on the activity and structural stability of the enzyme.
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Affiliation(s)
- Margarita C De Jesus
- Department of Chemistry and Biochemistry, Texas Woman's University, P.O. Box 425859, Denton, TX, 76204, USA
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6
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Abstract
One of the hallmarks of cancer is the ability to generate and withstand unusual levels of oxidative stress. In part, this property of tumor cells is conferred by elevation of the cellular redox buffer glutathione. Though enzymes of the glutathione synthesis and salvage pathways have been characterized for several decades, we still lack a comprehensive understanding of their independent and coordinate regulatory mechanisms. Recent studies have further revealed that overall central metabolic pathways are frequently altered in various tumor types, resulting in significant increases in biosynthetic capacity and feeding into glutathione synthesis. In this review, we will discuss the enzymes and pathways affecting glutathione flux in cancer and summarize current models for regulating cellular glutathione through both de novo synthesis and efficient salvage. In addition, we examine the integration of glutathione metabolism with other altered fates of intermediary metabolites and highlight remaining questions about molecular details of the accepted regulatory modes.
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Affiliation(s)
- Yilin Liu
- Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA
| | - Annastasia S Hyde
- Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA
| | - Melanie A Simpson
- Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA
| | - Joseph J Barycki
- Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA.
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Abstract
SIGNIFICANCE Parasitic infections continue to be a major problem for global human health. Vaccines are practically not available and chemotherapy is highly unsatisfactory. One approach toward a novel antiparasitic drug development is to unravel pathways that may be suited as future targets. Parasitic organisms show a remarkable diversity with respect to the nature and functions of their main low-molecular-mass antioxidants and many of them developed pathways that do not have a counterpart in their mammalian hosts. RECENT ADVANCES Work of the last years disclosed the individual antioxidants employed by parasites and their distinct pathways. Entamoeba, Trichomonas, and Giardia directly use cysteine as main low-molecular-mass thiol but have divergent cysteine metabolisms. Malarial parasites rely exclusively on cysteine uptake and generate glutathione (GSH) as main free thiol as do metazoan parasites. Trypanosomes and Leishmania have a unique trypanothione-based thiol metabolism but employ individual mechanisms for their cysteine supply. In addition, some trypanosomatids synthesize ovothiol A and/or ascorbate. Various essential parasite enzymes such as trypanothione synthetase and trypanothione reductase in Trypanosomatids and the Schistosoma thioredoxin GSH reductase are currently intensively explored as drug target molecules. CRITICAL ISSUES Essentiality is a prerequisite but not a sufficient property of an enzyme to become a suited drug target. The availability of an appropriate in vivo screening system and many other factors are equally important. FUTURE DIRECTIONS The current organism-wide RNA-interference and proteome analyses are supposed to reveal many more interesting candidates for future drug development approaches directed against the parasite antioxidant defense systems.
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Brown TR, Drummond ML, Barelier S, Crutchfield AS, Dinescu A, Slavens KD, Cundari TR, Anderson ME. Aspartate 458 of human glutathione synthetase is important for cooperativity and active site structure. Biochem Biophys Res Commun 2011; 411:536-42. [PMID: 21771585 DOI: 10.1016/j.bbrc.2011.06.166] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2011] [Accepted: 06/27/2011] [Indexed: 11/16/2022]
Abstract
Human glutathione synthetase (hGS) catalyzes the second ATP-dependent step in the biosynthesis of glutathione (GSH) and is negatively cooperative to the γ-glutamyl substrate. The hGS active site is composed of three highly conserved catalytic loops, notably the alanine rich A-loop. Experimental and computational investigations of the impact of mutation of Asp458 are reported, and thus the role of this A-loop residue on hGS structure, activity, negativity cooperativity and stability is defined. Several Asp458 hGS mutants (D458A, D458N and D458R) were constructed using site-directed mutagenesis and their activities determined (10%, 15% and 7% of wild-type hGS, respectively). The Michaelis-Menten constant (K(m)) was determined for all three substrates (glycine, GAB and ATP): glycine K(m) increased by 30-115-fold, GAB K(m) decreased by 8-17-fold, and the ATP K(m) was unchanged. All Asp458 mutants display a change in cooperativity from negative cooperativity to non-cooperative. All mutants show similar stability as compared to wild-type hGS, as determined by differential scanning calorimetry. The findings indicate that Asp458 is essential for hGS catalysis and that it impacts the allostery of hGS.
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Affiliation(s)
- Teresa R Brown
- Department of Chemistry and Physics, Texas Woman's University, Denton, TX 76204, United States
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9
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Slavens KD, Brown TR, Barakat KA, Cundari TR, Anderson ME. Valine 44 and valine 45 of human glutathione synthetase are key for subunit stability and negative cooperativity. Biochem Biophys Res Commun 2011; 410:597-601. [PMID: 21683691 DOI: 10.1016/j.bbrc.2011.06.034] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Accepted: 06/02/2011] [Indexed: 11/18/2022]
Abstract
It was hypothesized that residues Val44 and Val45 serve as important residues for human glutathione synthetase (hGS) function and stability given their location at the dimer interface of this enzyme. Computational studies suggest that mutation at Val45 has more impact on the structure and stability of hGS than does mutation at Val44. Experimentally, enzymes with mutations at the 44 and or 45 positions of hGS were prepared, purified and assayed for initial activity. Val45 position mutations (either to alanine or tryptophan) have a greater impact on enzyme activity than do mutations at Val44. Differential scanning calorimetry experiments reveal a loss of stability in all mutant enzymes, with V45 mutations being less stable than the corresponding Val44 mutations. The γ-GluABA substrate affinity remains unaltered in V44A and V45A mutant enzymes, but increases when tryptophan is introduced at either of these positions. Hill coefficients trend towards less negative cooperativity with the exception of V45W mutant hGS. These results imply that residues V44 and V45 are located along the allosteric pathway of this negatively cooperative dimeric enzyme, that their mutation impacts the allosteric pathway more than it does the active site of hGS, and that these residues (and by extension the dimer interface in which they are located) are integral to the stability of human glutathione synthetase.
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Affiliation(s)
- Kerri D Slavens
- Department of Chemistry and Physics, Texas Woman's University, Denton, TX 76204, USA
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10
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Sharma SK, Banyal HS. Characterization of Plasmodium berghei glutathione synthetase. Parasitol Int 2011; 60:321-3. [PMID: 21377539 DOI: 10.1016/j.parint.2011.02.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 02/18/2011] [Accepted: 02/28/2011] [Indexed: 11/16/2022]
Abstract
Plasmodium berghei contained 0.454±0.031 U/mg of glutathione synthetyase (GS). GS was purified using solid ammonium sulfate and Sephadex G-200 from P. berghei infected mouse erythrocytes. SDS-PAGE showed purified GS as a single band protein of 70 kDa and its Km for γ-glutamylcysteine, glycine and ATP being 0.33 mM, 8.3 mM and 0.43 mM respectively with noncompetitive inhibition by GSH. The malaria parasite enzyme was optimally active at 37°C and pH 8.0-8.5. Heavy metals significantly inhibited parasite GS activity.
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Affiliation(s)
- S K Sharma
- Department of Biosciences, Himachal Pradesh University, Shimla, India.
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11
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The role of the glycine triad in human glutathione synthetase. Biochem Biophys Res Commun 2010; 400:511-6. [PMID: 20800579 DOI: 10.1016/j.bbrc.2010.08.081] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 08/18/2010] [Indexed: 11/22/2022]
Abstract
Experimental kinetics and computational modeling of human glutathione synthetase (hGS) support the significant role of the G-loop glycine triad (G369, G370, G371) for activity of this ATP-grasp enzyme. Enzyme kinetic experiments indicate that G369V and G370V mutant hGS have little activity (<0.7 and 0.3%, respectively, versus wild-type hGS). However, G371V retains ∼13% of the activity of wild-type hGS. With respect to G-loop:A-loop interaction in hGS, mutations at Gly369 and Gly370 decrease ligand binding and prevent active site closure and protection. This research indicates that Gly369 and Gly370 have essential roles in hGS, while Gly371 has a lesser involvement. Implications for glycine-rich ensembles in other phosphate-binding enzymes are discussed.
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Subramanian K, Raghavan S, Rajan Bhat A, Das S, Bajpai Dikshit J, Kumar R, Narasimha MK, Nalini R, Radhakrishnan R, Raghunathan S. A systems biology based integrative framework to enhance the predictivity ofin vitromethods for drug-induced liver injury. Expert Opin Drug Saf 2008; 7:647-62. [DOI: 10.1517/14740330802501211] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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13
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Vergauwen B, De Vos D, Van Beeumen JJ. Characterization of the Bifunctional γ-Glutamate-cysteine Ligase/Glutathione Synthetase (GshF) of Pasteurella multocida. J Biol Chem 2006; 281:4380-94. [PMID: 16339152 DOI: 10.1074/jbc.m509517200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutamate-cysteine ligase (gamma-ECL) and glutathione synthetase (GS) are the two unrelated ligases that constitute the glutathione biosynthesis pathway in most eukaryotes, purple bacteria, and cyanobacteria. gamma-ECL is a member of the glutamine synthetase family, whereas GS enzymes group together with highly diverse carboxyl-to-amine/thiol ligases, all characterized by the so-called two-domain ATP-grasp fold. This generalized scheme toward the formation of glutathione, however, is incomplete, as functional steady-state levels of intracellular glutathione may also accumulate solely by import, as has been reported for the Pasteurellaceae member Haemophilus influenzae, as well as for certain Gram-positive enterococci and streptococci, or by the action of a bifunctional fusion protein (termed GshF), as has been reported recently for the Gram-positive firmicutes Streptococcus agalactiae and Listeria monocytogenes. Here, we show that yet another member of the Pasteurellaceae family, Pasteurella multocida, acquires glutathione both by import and GshF-driven biosynthesis. Domain architecture analysis shows that this P. multocida GshF bifunctional ligase contains an N-terminal gamma-proteobacterial gamma-ECL-like domain followed by a typical ATP-grasp domain, which most closely resembles that of cyanophycin synthetases, although it has no significant homology with known GS ligases. Recombinant P. multocida GshF overexpresses as an approximately 85-kDa protein, which, on the basis of gel-sizing chromatography, forms dimers in solution. The gamma-ECL activity of GshF is regulated by an allosteric type of glutathione feedback inhibition (K(i) = 13.6 mM). Furthermore, steady-state kinetics, on the basis of which we present a novel variant of half-of-the-sites reactivity, indicate intimate domain-domain interactions, which may explain the bifunctionality of GshF proteins.
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Affiliation(s)
- Bjorn Vergauwen
- Laboratory of Protein Biochemistry and Protein Engineering, Ghent University, Belgium
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14
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Gupta S, Srivastava AK, Banu N. Setaria cervi: kinetic studies of filarial glutathione synthetase by high performance liquid chromatography. Exp Parasitol 2005; 111:137-41. [PMID: 16087176 DOI: 10.1016/j.exppara.2005.06.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2005] [Revised: 06/23/2005] [Accepted: 06/26/2005] [Indexed: 11/25/2022]
Abstract
The bovine filarial worm Setaria cervi was found to have abundance of glutathione synthetase (GS; EC 6.3.2.3) activity, the enzyme being involved in catalysing the final step of glutathione (GSH) biosynthesis. A RP-HPLC method involving precolumn derivatization with o-phthalaldehyde has been followed for the estimation of GS activity in crude filarial preparations. Subcellular fractionation of the enzyme was undertaken and it was confirmed to be a soluble protein residing mainly in cytosolic fraction. Attempts to determine the Km value for L-gamma-glutamyl-L-cysteine gave a distinctly nonlinear double-reciprocal plot in which data obtained at relatively high dipeptide concentrations (>1 mM) extrapolate to a Km value of about 400 microM whereas data obtained at lower concentrations (<0.1 mM) extrapolate to a value of about 33 microM. Km was determined to be around 950 and 410 microM for ATP and glycine, respectively. The effect of various amino acids was studied on enzyme activity at 1mM concentration. L-cystine caused a significant enzyme inhibition of 11%. Preincubation with N-ethylmaleimide also resulted in significant inhibition of GS activity.
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Affiliation(s)
- Sapna Gupta
- Division of Biochemistry, Central Drug Research Institute, Lucknow 226 001, India.
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15
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Dinescu A, Cundari TR, Bhansali VS, Luo JL, Anderson ME. Function of conserved residues of human glutathione synthetase: implications for the ATP-grasp enzymes. J Biol Chem 2004; 279:22412-21. [PMID: 14990577 DOI: 10.1074/jbc.m401334200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutathione synthetase is an enzyme that belongs to the glutathione synthetase ATP-binding domain-like superfamily. It catalyzes the second step in the biosynthesis of glutathione from gamma-glutamylcysteine and glycine in an ATP-dependent manner. Glutathione synthetase has been purified and sequenced from a variety of biological sources; still, its exact mechanism is not fully understood. A variety of structural alignment methods were applied and four highly conserved residues of human glutathione synthetase (Glu-144, Asn-146, Lys-305, and Lys-364) were identified in the binding site. The function of these was studied by experimental and computational site-directed mutagenesis. The three-dimensional coordinates for several human glutathione synthetase mutant enzymes were obtained using molecular mechanics and molecular dynamics simulation techniques, starting from the reported crystal structure of human glutathione synthetase. Consistent with circular dichroism spectroscopy, our results showed no major changes to overall enzyme structure upon residue mutation. However, semiempirical calculations revealed that ligand binding is affected by these mutations. The key interactions between conserved residues and ligands were detected and found to be essential for enzymatic activity. Particularly, the negatively charged Glu-144 residue plays a major role in catalysis.
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Affiliation(s)
- Adriana Dinescu
- Departments of Chemistry and Biology, University of North Texas, Denton, Texas 76203, USA
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16
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Hackett NR, Heguy A, Harvey BG, O'Connor TP, Luettich K, Flieder DB, Kaplan R, Crystal RG. Variability of antioxidant-related gene expression in the airway epithelium of cigarette smokers. Am J Respir Cell Mol Biol 2003; 29:331-43. [PMID: 12702543 DOI: 10.1165/rcmb.2002-0321oc] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Cigarette smoking is the major risk factor for developing chronic bronchitis, yet only 15-20% of smokers develop this disorder. Because oxidants are the major mechanism of smoking-induced airway damage, we hypothesized that smoking is associated with upregulation of various antioxidant-related genes in the airway epithelium, but the magnitude of the response shows high inter-individual variability. Microarray analysis was used to assess levels of expression of 44 antioxidant-related genes in four categories (catalase/superoxide dismutase family; glutathione metabolism; redox balance; and pentose phosphate cycle) in bronchoscopy-obtained airway epithelium of matched cohorts (13 current smokers, 9 nonsmokers), none of whom had lung disease. There was minimal variation in gene expression levels within the same individual (right versus left lung or over time), but significant upregulation of 16/44 antioxidant-related genes in smoker epithelium compared with nonsmokers. Subgroups of smokers were identified with clusters of expression levels of antioxidant-related genes. We propose that the antioxidant-related genes demonstrating the most variability in the level of expression in smokers may be useful genetic markers in epidemiologic studies assessing susceptibility to smoking-induced chronic bronchitis.
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Affiliation(s)
- Neil R Hackett
- Belfer Gene Therapy Core Facility, Department of Genetic Medicine, Weill Medical College of Cornell University, New York, New York 10021, USA
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Abstract
GSH is the major low-molecular-mass thiol in most organisms. The tripeptide maintains a reduced intracellular environment and protects cellular components from damaging oxidation. GSH is synthesized by the action of two ATP-dependent enzymic steps, in which gamma-glutamylcysteine synthetase (gamma-GCS) catalyses the ligation of glutamate and cysteine and subsequently glutathione synthetase (GS) adds glycine to the dipeptide. Recently it was shown that the synthesis of gamma-glutamylcysteine is crucial for the survival of the erythrocytic stages of the malaria parasite Plasmodium falciparum by using the specific gamma-GCS inhibitor buthionine sulphoximine. In order to investigate further the synthetic pathway of the tripeptide in the parasite, GS was cloned and expressed recombinantly. The deduced amino acid sequence of P. falciparum GS shares only a moderate degree of identity with other known GSs, but the residues responsible for substrate and co-factor binding are almost all conserved, with the exception of the ones involved in gamma-glutamylcysteine binding. The protein is active as a dimer, with a subunit molecular mass of 77 kDa, and the addition of reducing reagents such as dithiothreitol is essential in maintaining enzymic activity, indicating that thiol groups are important for stability and enzymic activity. The K(app)(m) values for gamma-glutamyl-alpha-aminobutyrate, ATP and glycine were determined to be 107.1 microM, 59.1 microM and 5.04 mM, respectively, and the V(max) of 5.24 +/- 0.7 micromol.min(-1).mg(-1) was in the same range as that of the mammalian enzymes. However, the negative co-operativity observed for gamma-glutamylcysteine binding to the rat enzyme was not found for the parasite protein. This may be due to the alteration of several amino acids in the gamma-glutamylcysteine-binding site.
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Affiliation(s)
- Svenja Meierjohann
- Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, MSI/WTB complex, University of Dundee, Dundee DD1 5EH, Scotland, UK
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Njalsson R, Norgren S, Larsson A, Huang CS, Anderson ME, Luo JL. Cooperative binding of gamma-glutamyl substrate to human glutathione synthetase. Biochem Biophys Res Commun 2001; 289:80-4. [PMID: 11708780 DOI: 10.1006/bbrc.2001.5961] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human glutathione synthetase is responsible for catalyzing the final step in glutathione biosynthesis. It is a homodimer with a monomer subunit MW of 52 kDa. Kinetic analysis reveals a departure from linearity of the Lineweaver-Burk double reciprocal plot for the binding of gamma-glutamyl substrate, indicating cooperative binding. The measured apparent K(m) values for gamma-glutamyl-alpha-aminobutyrate (an analog of gamma-glutamyl-alpha-aminobutyrate) are 63 and 164 microM, respectively. Neither ATP (K(m) of 248 microM) nor glycine (K(m) of 452 microM) exhibits such cooperative binding behavior. Although ATP is proposed to play a key role in the sequential binding of gamma-glutamyl substrate to the enzyme, the cooperative binding of the gamma-glutamyl substrate is not affected by alterations of ATP concentration. Quantitative analysis of the kinetic results for gamma-glutamyl substrate binding gives a Hill coefficient (h) of 0.75, indicating negative cooperativity. Our studies, for the first time, show that human glutathione synthetase is an allosteric enzyme with cooperative binding for gamma-glutamyl substrate.
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Affiliation(s)
- R Njalsson
- Department of Pediatrics, Karolinska Institute, Huddinge University Hospital, 141 86 Huddinge, Sweden
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