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Lahham M, Jha S, Goj D, Macheroux P, Wallner S. The family of sarcosine oxidases: Same reaction, different products. Arch Biochem Biophys 2021; 704:108868. [PMID: 33812916 DOI: 10.1016/j.abb.2021.108868] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/26/2021] [Accepted: 03/27/2021] [Indexed: 12/11/2022]
Abstract
The subfamily of sarcosine oxidase is a set of enzymes within the larger family of amine oxidases. It is ubiquitously distributed among different kingdoms of life. The member enzymes catalyze the oxidization of an N-methyl amine bond of amino acids to yield unstable imine species that undergo subsequent spontaneous non-enzymatic reactions, forming an array of different products. These products range from demethylated simple species to complex alkaloids. The enzymes belonging to the sarcosine oxidase family, namely, monomeric and heterotetrameric sarcosine oxidase, l-pipecolate oxidase, N-methyltryptophan oxidase, NikD, l-proline dehydrogenase, FsqB, fructosamine oxidase and saccharopine oxidase have unique features differentiating them from other amine oxidases. This review highlights the key attributes of the sarcosine oxidase family enzymes, in terms of their substrate binding motif, type of oxidation reaction mediated and FAD regeneration, to define the boundaries of this group and demarcate these enzymes from other amine oxidase families.
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Affiliation(s)
- Majd Lahham
- Institute of Biochemistry, Graz University of Technology, NAWI Graz, Graz, Austria; Department of Biochemistry and Microbiology, Aljazeera Private University, Ghabagheb, Syria
| | - Shalinee Jha
- Institute of Biochemistry, Graz University of Technology, NAWI Graz, Graz, Austria
| | - Dominic Goj
- Institute of Biochemistry, Graz University of Technology, NAWI Graz, Graz, Austria
| | - Peter Macheroux
- Institute of Biochemistry, Graz University of Technology, NAWI Graz, Graz, Austria
| | - Silvia Wallner
- Institute of Biochemistry, Graz University of Technology, NAWI Graz, Graz, Austria.
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2
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Preparation, reconstruction, and characterization of a predicted Thermomicrobium roseum sarcosine oxidase. MOLECULAR CATALYSIS 2018. [DOI: 10.1016/j.mcat.2018.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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3
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Abe Y, Shoji M, Nishiya Y, Aiba H, Kishimoto T, Kitaura K. The reaction mechanism of sarcosine oxidase elucidated using FMO and QM/MM methods. Phys Chem Chem Phys 2017; 19:9811-9822. [DOI: 10.1039/c6cp08172j] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Monomeric sarcosine oxidase (MSOX) is a flavoprotein that oxidizes sarcosine to the corresponding imine product and is widely used in clinical diagnostics to test renal function.
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Affiliation(s)
| | - Mitsuo Shoji
- Center for Computational Sciences
- University of Tsukuba
- Tsukuba
- Japan
| | - Yoshiaki Nishiya
- Department of Life Science
- Faculty of Science and Engineering
- Setsunan University
- Neyagawa
- Japan
| | - Hiroshi Aiba
- Tsuruga Institute of Biotechnology
- TOYOBO Co., Ltd
- Tsuruga
- Japan
| | | | - Kazuo Kitaura
- Fukui Institute for Fundamental Chemistry
- Kyoto University
- Sakyou-ku
- Japan
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4
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Approaches to the solution of coupled multiexponential transient-state rate kinetic equations: A critical review. Arch Biochem Biophys 2016; 603:54-63. [PMID: 27173736 DOI: 10.1016/j.abb.2016.05.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 05/02/2016] [Accepted: 05/03/2016] [Indexed: 11/23/2022]
Abstract
The transient-state kinetic approach has failed to reach its full potential despite its advantage over the steady-state approach in its ability to observe mechanistic events directly and in real time. This failure has been due in part to the lack of any rigorously derived and readily applicable body of theory corresponding to that which currently characterizes the steady-state approach. In order to clarify the causes of this discrepancy and to suggest a route to its solution we examine the capabilities and limitations of the various forms of transient-state kinetic approaches to the mathematical resolution of enzymatic reaction mechanisms currently available. We document a lack of validity inherent in their basic assumptions and suggest the need for a potentially more rigorous analytic approach.
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5
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Karasulu B, Thiel W. Amine Oxidation Mediated by N-Methyltryptophan Oxidase: Computational Insights into the Mechanism, Role of Active-Site Residues, and Covalent Flavin Binding. ACS Catal 2015. [DOI: 10.1021/cs501694q] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Bora Karasulu
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz
1, 45470 Mülheim, Germany
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz
1, 45470 Mülheim, Germany
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6
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Rapid method using two microbial enzymes for detection of L-abrine in food as a marker for the toxic protein abrin. Appl Environ Microbiol 2014; 81:1610-5. [PMID: 25527549 DOI: 10.1128/aem.03492-14] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abrin is a toxic protein produced by the ornamental plant Abrus precatorius, and it is of concern as a biothreat agent. The small coextracting molecule N-methyl-l-tryptophan (l-abrine) is specific to members of the genus Abrus and thus can be used as a marker for the presence or ingestion of abrin. Current methods for the detection of abrin or l-abrine in foods and other matrices require complex sample preparation and expensive instrumentation. To develop a fast and portable method for the detection of l-abrine in beverages and foods, the Escherichia coli proteins N-methyltryptophan oxidase (MTOX) and tryptophanase were expressed and purified. The two enzymes jointly degraded l-abrine to products that included ammonia and indole, and colorimetric assays for the detection of those analytes in beverage and food samples were evaluated. An indole assay using a modified version of Ehrlich's/Kovac's reagent was more sensitive and less subject to negative interferences from components in the samples than the Berthelot ammonia assay. The two enzymes were added into food and beverage samples spiked with l-abrine, and indole was detected as a degradation product, with the visual lower detection limit being 2.5 to 10.0 μM (∼0.6 to 2.2 ppm) l-abrine in the samples tested. Results could be obtained in as little as 15 min. Sample preparation was limited to pH adjustment of some samples. Visual detection was found to be about as sensitive as detection with a spectrophotometer, especially in milk-based matrices.
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7
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Fitzpatrick PF. Combining solvent isotope effects with substrate isotope effects in mechanistic studies of alcohol and amine oxidation by enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2014; 1854:1746-55. [PMID: 25448013 DOI: 10.1016/j.bbapap.2014.10.020] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Revised: 10/17/2014] [Accepted: 10/20/2014] [Indexed: 10/24/2022]
Abstract
Oxidation of alcohols and amines is catalyzed by multiple families of flavin- and pyridine nucleotide-dependent enzymes. Measurement of solvent isotope effects provides a unique mechanistic probe of the timing of the cleavage of the OH and NH bonds, necessary information for a complete description of the catalytic mechanism. The inherent ambiguities in interpretation of solvent isotope effects can be significantly decreased if isotope effects arising from isotopically labeled substrates are measured in combination with solvent isotope effects. The application of combined solvent and substrate (mainly deuterium) isotope effects to multiple enzymes is described here to illustrate the range of mechanistic insights that such an approach can provide. This article is part of a Special Issue entitled: Enzyme Transition States from Theory and Experiment.
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Affiliation(s)
- Paul F Fitzpatrick
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX 78212, USA.
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8
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Kong X, Ouyang S, Liang Z, Lu J, Chen L, Shen B, Li D, Zheng M, Li KK, Luo C, Jiang H. Catalytic mechanism investigation of lysine-specific demethylase 1 (LSD1): a computational study. PLoS One 2011; 6:e25444. [PMID: 21984927 PMCID: PMC3184146 DOI: 10.1371/journal.pone.0025444] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 09/05/2011] [Indexed: 12/13/2022] Open
Abstract
Lysine-specific demethylase 1 (LSD1), the first identified histone demethylase, is a flavin-dependent amine oxidase which specifically demethylates mono- or dimethylated H3K4 and H3K9 via a redox process. It participates in a broad spectrum of biological processes and is of high importance in cell proliferation, adipogenesis, spermatogenesis, chromosome segregation and embryonic development. To date, as a potential drug target for discovering anti-tumor drugs, the medical significance of LSD1 has been greatly appreciated. However, the catalytic mechanism for the rate-limiting reductive half-reaction in demethylation remains controversial. By employing a combined computational approach including molecular modeling, molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) calculations, the catalytic mechanism of dimethylated H3K4 demethylation by LSD1 was characterized in details. The three-dimensional (3D) model of the complex was composed of LSD1, CoREST, and histone substrate. A 30-ns MD simulation of the model highlights the pivotal role of the conserved Tyr761 and lysine-water-flavin motif in properly orienting flavin adenine dinucleotide (FAD) with respect to substrate. The synergy of the two factors effectively stabilizes the catalytic environment and facilitated the demethylation reaction. On the basis of the reasonable consistence between simulation results and available mutagenesis data, QM/MM strategy was further employed to probe the catalytic mechanism of the reductive half-reaction in demethylation. The characteristics of the demethylation pathway determined by the potential energy surface and charge distribution analysis indicates that this reaction belongs to the direct hydride transfer mechanism. Our study provides insights into the LSD1 mechanism of reductive half-reaction in demethylation and has important implications for the discovery of regulators against LSD1 enzymes.
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Affiliation(s)
- Xiangqian Kong
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Sisheng Ouyang
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Zhongjie Liang
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Junyan Lu
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Liang Chen
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Bairong Shen
- Center for Systems Biology, Soochow University, Jiangsu, China
| | - Donghai Li
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Jiangsu Diabetes Research Center, Nanjing University, Nanjing, China
| | - Mingyue Zheng
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Keqin Kathy Li
- State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- * E-mail: (CL); (KKL)
| | - Cheng Luo
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
- Center for Systems Biology, Soochow University, Jiangsu, China
- * E-mail: (CL); (KKL)
| | - Hualiang Jiang
- State Key Laboratory of Drug Research, Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
- School of Pharmacy, East China University of Science and Technology, Shanghai, China
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9
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Bruckner RC, Winans J, Jorns MS. Pleiotropic impact of a single lysine mutation on biosynthesis of and catalysis by N-methyltryptophan oxidase. Biochemistry 2011; 50:4949-62. [PMID: 21526853 DOI: 10.1021/bi200349m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N-Methyltryptophan oxidase (MTOX) contains covalently bound FAD. N-Methyltryptophan binds in a cavity above the re face of the flavin ring. Lys259 is located above the opposite, si face. Replacement of Lys259 with Gln, Ala, or Met blocks (>95%) covalent flavin incorporation in vivo. The mutant apoproteins can be reconstituted with FAD. Apparent turnover rates (k(cat,app)) of the reconstituted enzymes are ~2500-fold slower than those of wild-type MTOX. Wild-type MTOX forms a charge-transfer E(ox)·S complex with the redox-active anionic form of NMT. The E(ox)·S complex formed with Lys259Gln does not exhibit a charge-transfer band and is converted to a reduced enzyme·imine complex (EH(2)·P) at a rate 60-fold slower than that of wild-type MTOX. The mutant EH(2)·P complex contains the imine zwitterion and exhibits a charge-transfer band, a feature not observed with the wild-type EH(2)·P complex. Reaction of reduced Lys259Gln with oxygen is 2500-fold slower than that of reduced wild-type MTOX. The latter reaction is unaffected by the presence of bound product. Dissociation of the wild-type EH(2)·P complex is 80-fold slower than k(cat). The mutant EH(2)·P complex dissociates 15-fold faster than k(cat,app). Consequently, EH(2)·P and free EH(2) are the species that react with oxygen during turnover of the wild-type and mutant enzyme, respectively. The results show that (i) Lys259 is the site of oxygen activation in MTOX and also plays a role in holoenzyme biosynthesis and N-methyltryptophan oxidation and (ii) MTOX contains separate active sites for N-methyltryptophan oxidation and oxygen reduction on opposite faces of the flavin ring.
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Affiliation(s)
- Robert C Bruckner
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, USA
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10
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Moriguchi T, Ida K, Hikima T, Ueno G, Yamamoto M, Suzuki H. Channeling and conformational changes in the heterotetrameric sarcosine oxidase from Corynebacterium sp. U-96. ACTA ACUST UNITED AC 2010; 148:491-505. [DOI: 10.1093/jb/mvq083] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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11
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Adachi MS, Juarez PR, Fitzpatrick PF. Mechanistic studies of human spermine oxidase: kinetic mechanism and pH effects. Biochemistry 2010; 49:386-92. [PMID: 20000632 PMCID: PMC2810717 DOI: 10.1021/bi9017945] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In mammalian cells, the flavoprotein spermine oxidase (SMO) catalyzes the oxidation of spermine to spermidine and 3-aminopropanal. Mechanistic studies have been conducted with the recombinant human enzyme. The initial velocity pattern in which the ratio between the concentrations of spermine and oxygen is kept constant establishes the steady-state kinetic pattern as ping-pong. Reduction of SMO by spermine in the absence of oxygen is biphasic. The rate constant for the rapid phase varies with the substrate concentration, with a limiting value (k(3)) of 49 s(-1) and an apparent K(d) value of 48 microM at pH 8.3. The rate constant for the slow step is independent of the spermine concentration, with a value of 5.5 s(-1), comparable to the k(cat) value of 6.6 s(-1). The kinetics of the oxidative half-reaction depend on the aging time after the spermine and enzyme are mixed in a double-mixing experiment. At an aging time of 6 s, the reaction is monophasic with a second-order rate constant of 4.2 mM(-1) s(-1). At an aging time of 0.3 s, the reaction is biphasic with two second-order constants equal to 4.0 and 40 mM(-1) s(-1). Neither is equal to the k(cat)/K(O(2)) value of 13 mM(-1) s(-1). These results establish the existence of more than one pathway for the reaction of the reduced flavin intermediate with oxygen. The k(cat)/K(M) value for spermine exhibits a bell-shaped pH profile, with an average pK(a) value of 8.3. This profile is consistent with the active form of spermine having three charged nitrogens. The pH profile for k(3) shows a pK(a) value of 7.4 for a group that must be unprotonated. The pK(i)-pH profiles for the competitive inhibitors N,N'-dibenzylbutane-1,4-diamine and spermidine show that the fully protonated forms of the inhibitors and the unprotonated form of an amino acid residue with a pK(a) of approximately 7.4 in the active site are preferred for binding.
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Affiliation(s)
- Maria S. Adachi
- Department of Biochemistry and Center for Biomedical Neuroscience, University of Texas Health Science Center, San Antonio, TX 78229
| | - Paul R. Juarez
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Paul F. Fitzpatrick
- Department of Biochemistry and Center for Biomedical Neuroscience, University of Texas Health Science Center, San Antonio, TX 78229
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12
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Oxidation of amines by flavoproteins. Arch Biochem Biophys 2009; 493:13-25. [PMID: 19651103 DOI: 10.1016/j.abb.2009.07.019] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Revised: 07/27/2009] [Accepted: 07/29/2009] [Indexed: 11/21/2022]
Abstract
Many flavoproteins catalyze the oxidation of primary and secondary amines, with the transfer of a hydride equivalent from a carbon-nitrogen bond to the flavin cofactor. Most of these amine oxidases can be classified into two structural families, the D-amino acid oxidase/sarcosine oxidase family and the monoamine oxidase family. This review discusses the present understanding of the mechanisms of amine and amino acid oxidation by flavoproteins, focusing on these two structural families.
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13
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Gaweska H, Henderson Pozzi M, Schmidt DMZ, McCafferty DG, Fitzpatrick PF. Use of pH and kinetic isotope effects to establish chemistry as rate-limiting in oxidation of a peptide substrate by LSD1. Biochemistry 2009; 48:5440-5. [PMID: 19408960 DOI: 10.1021/bi900499w] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The mechanism of oxidation of a peptide substrate by the flavoprotein lysine-specific demethylase (LSD1) has been examined using the effects of pH and isotopic substitution on steady-state and rapid-reaction kinetic parameters. The substrate contained the 21 N-terminal residues of histone H3, with a dimethylated lysyl residue at position 4. At pH 7.5, the rate constant for flavin reduction, k(red), equals k(cat), establishing the reductive half-reaction as rate-limiting at physiological pH. Deuteration of the lysyl methyls results in identical kinetic isotope effects of 3.1 +/- 0.2 on the k(red), k(cat), and k(cat)/K(m) values for the peptide, establishing C-H bond cleavage as rate-limiting with this substrate. No intermediates between oxidized and reduced flavin can be detected by stopped-flow spectroscopy, consistent with the expectation for a direct hydride transfer mechanism. The k(cat)/K(m) value for the peptide is bell-shaped, consistent with a requirement that the nitrogen at the site of oxidation be uncharged and that at least one of the other lysyl residues be charged for catalysis. The (D)(k(cat)/K(m)) value for the peptide is pH-independent, suggesting that the observed value is the intrinsic deuterium kinetic isotope effect for oxidation of this substrate.
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Affiliation(s)
- Helena Gaweska
- Department of Biochemistry and Biophysics and Johnson Research Foundation, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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14
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Ilari A, Bonamore A, Franceschini S, Fiorillo A, Boffi A, Colotti G. The X-ray structure of N-methyltryptophan oxidase reveals the structural determinants of substrate specificity. Proteins 2008; 71:2065-75. [PMID: 18186483 DOI: 10.1002/prot.21898] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The X-ray structure of monomeric N-methyltryptophan oxidase from Escherichia coli (MTOX) has been solved at 3.2 A resolution by molecular replacement methods using Bacillus sp. sarcosine oxidase structure (MSOX, 43% sequence identity) as search model. The analysis of the substrate binding site highlights the structural determinants that favour the accommodation of the bulky N-methyltryptophan residue in MTOX. In fact, although the nature and geometry of the catalytic residues within the first contact shell of the FAD moiety appear to be virtually superposable in MTOX and MSOX, the presence of a Thr residue in position 239 in MTOX (Met245 in MSOX) located at the entrance of the active site appears to play a key role for the recognition of the amino acid substrate side chain. Accordingly, a 15 fold increase in k(cat) and 100 fold decrease in K(m) for sarcosine as substrate has been achieved in MTOX upon T239M mutation, with a concomitant three-fold decrease in activity towards N-methyltryptophan. These data provide clear evidence for the presence of a catalytic core, common to the members of the methylaminoacid oxidase subfamily, and of a side chain recognition pocket, located at the entrance of the active site, that can be adjusted to host diverse aminoacids in the different enzyme species. The site involved in the covalent attachment of flavin has also been addressed by screening degenerate mutants in the relevant positions around Cys308-FAD linkage. Lys341 appears to be the key residue involved in flavin incorporation and covalent linkage.
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Affiliation(s)
- Andrea Ilari
- Institute of Molecular Biology and Pathology, C.N.R., Rome, Italy
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15
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Ralph EC, Anderson MA, Cleland WW, Fitzpatrick PF. Mechanistic studies of the flavoenzyme tryptophan 2-monooxygenase: deuterium and 15N kinetic isotope effects on alanine oxidation by an L-amino acid oxidase. Biochemistry 2008; 45:15844-52. [PMID: 17176107 PMCID: PMC1994567 DOI: 10.1021/bi061894o] [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: 11/29/2022]
Abstract
Tryptophan 2-monooxygenase (TMO) from Pseudomonas savastanoi catalyzes the oxidative decarboxylation of l-tryptophan during the biosynthesis of indoleacetic acid. Structurally and mechanistically, the enzyme is a member of the family of l-amino acid oxidases. Deuterium and 15N kinetic isotope effects were used to probe the chemical mechanism of l-alanine oxidation by TMO. The primary deuterium kinetic isotope effect was pH independent over the pH range 6.5-10, with an average value of 6.0 +/- 0.5, consistent with this being the intrinsic value. The deuterium isotope effect on the rate constant for flavin reduction by alanine was 6.3 +/- 0.9; no intermediate flavin species were observed during flavin reduction. The kcat/Kala value was 1.0145 +/- 0.0007 at pH 8. NMR analyses gave an equilibrium 15N isotope effect for deprotonation of the alanine amino group of 1.0233 +/- 0.0004, allowing calculation of the 15N isotope effect on the CH bond cleavage step of 0.9917 +/- 0.0006. The results are consistent with TMO oxidation of alanine occurring through a hydride transfer mechanism.
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Affiliation(s)
- Erik C. Ralph
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
| | - Mark A. Anderson
- Institute for Enzyme Research and Department of Biochemistry, University of Wisconsin, Madison, WI
| | - W. Wallace Cleland
- Institute for Enzyme Research and Department of Biochemistry, University of Wisconsin, Madison, WI
| | - Paul F. Fitzpatrick
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
- Department of Chemistry, Texas A&M University, College Station, TX 77843-2128
- *Address correspondence to:Paul F. Fitzpatrick,.Department of Biochemistry and Biophysics, 2128 TAMU, College Station, TX 77843-2128, Ph: 979-845-5487, Fax: 979-845-4946,
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16
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Tsai CL, Gokulan K, Sobrado P, Sacchettini JC, Fitzpatrick PF. Mechanistic and structural studies of H373Q flavocytochrome b2: effects of mutating the active site base. Biochemistry 2007; 46:7844-51. [PMID: 17563122 PMCID: PMC2526232 DOI: 10.1021/bi7005543] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
His373 in flavocytochrome b2 has been proposed to act as an active site base during the oxidation of lactate to pyruvate, most likely by removing the lactate hydroxyl proton. The effects of mutating this residue to glutamine have been determined to provide further insight into its role. The kcat and kcat/Klactate values for the mutant protein are 3 to 4 orders of magnitude smaller than the wild-type values, consistent with a critical role for His373. Similar effects are seen when the mutation is incorporated into the isolated flavin domain of the enzyme, narrowing the effects to lactate oxidation rather than subsequent electron transfers. The decrease of 3500-fold in the rate constant for reduction of the enzyme-bound FMN by lactate confirms this part of the reaction as that most effected by the mutation. The primary deuterium and solvent kinetic isotope effects for the mutant enzyme are significantly smaller than the wild-type values, establishing that bond cleavage steps are less rate-limiting in H373Q flavocytochrome b2 than in the wild-type enzyme. The structure of the mutant enzyme with pyruvate bound, determined at 2.8 A, provides a rationale for these effects. The orientation of pyruvate in the active site is altered from that seen in the wild-type enzyme. In addition, the active site residues Arg289, Asp 292, and Leu 286 have altered positions in the mutant protein. The combination of an altered active site and the small kinetic isotope effects is consistent with the slowest step in turnover being a conformational change involving a conformation in which lactate is bound unproductively.
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Affiliation(s)
- Chi-Lin Tsai
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
| | - Kuppan Gokulan
- Department of Biochemistry and Biophysics , Texas A&M University, College Station TX 77843-2128
| | - Pablo Sobrado
- Department of Biochemistry and Biophysics , Texas A&M University, College Station TX 77843-2128
| | - James C. Sacchettini
- Department of Biochemistry and Biophysics , Texas A&M University, College Station TX 77843-2128
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
| | - Paul F. Fitzpatrick
- Department of Biochemistry and Biophysics , Texas A&M University, College Station TX 77843-2128
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
- *Address correspondence to: Paul F. Fitzpatrick, Department of Biochemistry and Biophysics, 2128 TAMU, College Station, TX 77843-2128; Ph: 979-845-5487; Fax: 979-845-4946;
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17
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Ralph EC, Hirschi JS, Anderson MA, Cleland WW, Singleton DA, Fitzpatrick PF. Insights into the mechanism of flavoprotein-catalyzed amine oxidation from nitrogen isotope effects on the reaction of N-methyltryptophan oxidase. Biochemistry 2007; 46:7655-64. [PMID: 17542620 PMCID: PMC2041825 DOI: 10.1021/bi700482h] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism of N-methyltryptophan oxidase, a flavin-dependent amine oxidase from Escherichia coli, was studied using a combination of kinetic isotope effects and theoretical calculations. The 15(kcat/Km) kinetic isotope effect for sarcosine oxidation is pH-dependent with a limiting value of 0.994-0.995 at high pH. Density functional theory calculations on model systems were used to interpret these isotope effects. The isotope effects are inconsistent with proposed mechanisms involving covalent amine-flavin adducts but cannot by themselves conclusively distinguish between some discrete electron-transfer mechanisms and a direct hydride-transfer mechanism, although the latter mechanism is more consistent with the energetics of the reaction.
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Affiliation(s)
- Erik C. Ralph
- Department of Biochemistry and Biophysics, Texas A&M University, College Station TX 77843-2128
| | - Jennifer S. Hirschi
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
| | - Mark A. Anderson
- Institute for Enzyme Research and Department of Biochemistry University of Wisconsin, Madison, WI
| | - W. Wallace Cleland
- Institute for Enzyme Research and Department of Biochemistry University of Wisconsin, Madison, WI
| | - Daniel A. Singleton
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
- *Corresponding authors. D.A.S.: phone, 979-845-9166; fax 979-845-0653; e-mail, . P.F.F.: phone, 979-845-5487; fax 979-845-4946; e-mail,
| | - Paul F. Fitzpatrick
- Department of Biochemistry and Biophysics, Texas A&M University, College Station TX 77843-2128
- Department of Chemistry, Texas A&M University, College Station TX 77843-2128
- *Corresponding authors. D.A.S.: phone, 979-845-9166; fax 979-845-0653; e-mail, . P.F.F.: phone, 979-845-5487; fax 979-845-4946; e-mail,
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Fitzpatrick PF. Insights into the mechanisms of flavoprotein oxidases from kinetic isotope effects. J Labelled Comp Radiopharm 2007; 50:1016-1025. [PMID: 19890477 DOI: 10.1002/jlcr.1400] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Deuterium, solvent, and (15)N kinetic isotope effects have been used to probe the mechanisms by which flavoproteins oxidize carbon-oxygen and carbon-nitrogen bonds in amines, hydroxy acids, and alcohols. For the amine oxidases d-amino acid oxidase, N-methyltryptophan oxidase, and tryptophan monooxygenase, d-serine, sarcosine, and alanine are slow substrates for which CH bond cleavage is fully rate limiting. Inverse isotope effects for each of 0.992-0.996 are consistent with a common mechanism involving hydride transfer from the uncharged amine. Computational analyses of possible mechanisms support this conclusion. Deuterium and solvent isotope effects with wild-type and mutant variants of the lactate dehydrogenase flavocytochrome b(2) show that OH and CH bond cleavage are not concerted, but become so in the Y254F enzyme. This is consistent with a highly asynchronous reaction in which OH bond cleavage precedes hydride transfer. The results of Hammett analyses and solvent and deuterium isotope effects support a similar mechanism for alcohol oxidase.
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Affiliation(s)
- Paul F Fitzpatrick
- Departments of Biochemistry and Biophysics and of Chemistry, Texas A&M University, College Station, TX 77843-2128, USA
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