1
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Manesis AC, Slater JW, Cantave K, Martin Bollinger J, Krebs C, Rosenzweig AC. Capturing a bis-Fe(IV) State in Methylosinus trichosporium OB3b MbnH. Biochemistry 2023; 62:1082-1092. [PMID: 36812111 PMCID: PMC10083075 DOI: 10.1021/acs.biochem.3c00021] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
The diheme bacterial cytochrome c peroxidase (bCcP)/MauG superfamily is a diverse set of enzymes that remains largely uncharacterized. One recently discovered member, MbnH, converts a tryptophan residue in its substrate protein, MbnP, to kynurenine. Here we show that upon reaction with H2O2, MbnH forms a bis-Fe(IV) intermediate, a state previously detected in just two other enzymes, MauG and BthA. Using absorption, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopies coupled with kinetic analysis, we characterized the bis-Fe(IV) state of MbnH and determined that this intermediate decays back to the diferric state in the absence of MbnP substrate. In the absence of MbnP substrate, MbnH can also detoxify H2O2 to prevent oxidative self damage, unlike MauG, which has long been viewed as the prototype for bis-Fe(IV) forming enzymes. MbnH performs a different reaction from MauG, while the role of BthA remains unclear. All three enzymes can form a bis-Fe(IV) intermediate but within distinct kinetic regimes. The study of MbnH significantly expands our knowledge of enzymes that form this species. Computational and structural analyses indicate that electron transfer between the two heme groups in MbnH and between MbnH and the target tryptophan in MbnP likely occurs via a hole-hopping mechanism involving intervening tryptophan residues. These findings set the stage for discovery of additional functional and mechanistic diversity within the bCcP/MauG superfamily.
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Affiliation(s)
- Anastasia C Manesis
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Jeffrey W Slater
- Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Kenny Cantave
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - J Martin Bollinger
- Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Carsten Krebs
- Department of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Amy C Rosenzweig
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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2
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Singha A, Mittra K, Dey A. Synthetic heme dioxygen adducts: electronic structure and reactivity. TRENDS IN CHEMISTRY 2022. [DOI: 10.1016/j.trechm.2021.10.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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3
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Gallio A, Fung SSP, Cammack-Najera A, Hudson AJ, Raven EL. Understanding the Logistics for the Distribution of Heme in Cells. JACS AU 2021; 1:1541-1555. [PMID: 34723258 PMCID: PMC8549057 DOI: 10.1021/jacsau.1c00288] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Indexed: 05/03/2023]
Abstract
Heme is essential for the survival of virtually all living systems-from bacteria, fungi, and yeast, through plants to animals. No eukaryote has been identified that can survive without heme. There are thousands of different proteins that require heme in order to function properly, and these are responsible for processes such as oxygen transport, electron transfer, oxidative stress response, respiration, and catalysis. Further to this, in the past few years, heme has been shown to have an important regulatory role in cells, in processes such as transcription, regulation of the circadian clock, and the gating of ion channels. To act in a regulatory capacity, heme needs to move from its place of synthesis (in mitochondria) to other locations in cells. But while there is detailed information on how the heme lifecycle begins (heme synthesis), and how it ends (heme degradation), what happens in between is largely a mystery. Here we summarize recent information on the quantification of heme in cells, and we present a discussion of a mechanistic framework that could meet the logistical challenge of heme distribution.
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Affiliation(s)
- Andrea
E. Gallio
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Simon S.-P. Fung
- Department
of Chemistry and Leicester Institute of Structural and Chemical Biology, University of Leicester, Leicester LE1 7RH, U.K.
| | - Ana Cammack-Najera
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Andrew J. Hudson
- Department
of Chemistry and Leicester Institute of Structural and Chemical Biology, University of Leicester, Leicester LE1 7RH, U.K.
| | - Emma L. Raven
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
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4
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Fan X, Lim J, Li Z, Wang T, Jiang L, Liu S, Zhou L, He C. GOX-hemin nanogels with enhanced cascade activity for sensitive one-step glucose detection. J Mater Chem B 2021; 9:3509-3514. [PMID: 33909733 DOI: 10.1039/d1tb00191d] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Early glucose detection is important in both healthy people and diabetic patients. The glucose colorimetric detection techniques usually consist of multiple steps and their preparation processes are time consuming. In this work, we fabricate a GOX-hemin nanogel (GHN) that could be used for one-step colorimetry detection of glucose. The GHN was prepared by carrying out polymerization on the surface of GOX. Each GOX-hemin nanogel consists of a single GOX encapsulated with a thin polymer network containing hemin. The proximity of hemin to GOX facilitates two reactions, i.e. the oxidation of glucose catalysed by GOX to yield H2O2, and the subsequent 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction catalysed by hemin to yield the blue colored product. These processes work in tandem, which greatly enhances the efficacy, sensitivity and stability of the detection system. The limit of detection in our system was determined to be as low as 4 μM. Furthermore, the glucose detection activity still maintained more than 70% even after being incubated at 55 °C for 30 minutes, or in 20% (v/v) aqueous solution of DMF, CH3CN or THF for 25 minutes at room temperature. It is anticipated that this work can provide a method for developing diverse functional materials based on proteins.
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Affiliation(s)
- Xiaotong Fan
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore.
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5
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Yuasa HJ, Stocker R. Methylene blue and ascorbate interfere with the accurate determination of the kinetic properties of IDO2. FEBS J 2021; 288:4892-4904. [PMID: 33686747 DOI: 10.1111/febs.15806] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2020] [Revised: 02/16/2021] [Accepted: 03/08/2021] [Indexed: 11/30/2022]
Abstract
Indoleamine 2,3-dioxygenases (IDOs) catalyze the oxidative cleavage of L-tryptophan (Trp) to N-formylkynurenine. Two IDOs, IDO1 and IDO2, are present in vertebrates. IDO1 is a high-affinity Trp-degrading enzyme involved in several physiological processes. By comparison, IDO2 generally has been reported to have low affinity (high Km -value) for Trp, and the enzyme's in vivo function remains unclear. Using IDOs from different species, we show that compared with ferrous-oxy (Fe2+ -O2 ) IDO1, Fe2+ -O2 IDO2 is substantially more stable and engages in multiple turnovers of the reaction in the absence of a reductant. Without reductant, Fe2+ -O2 IDO2 showed Km -values in the range of 80-356 μM, that is, values substantially lower than reported previously and close to the physiological concentrations of Trp. Methylene blue and ascorbate (Asc), used commonly as the reducing system for IDO activity determination, significantly affected the enzymatic activity of IDO2: In combination, the two reductants increased the apparent Km - and kcat -values 8- to 117-fold and 2-fold, respectively. Asc alone both activated and inhibited IDO2 by acting as a source of electrons and as a weak competitive inhibitor, respectively. In addition, ferric (Fe3+ ) IDO1 and IDO2 exhibited weak dioxygenase activity, similar to tryptophan 2,3-dioxygenase. Our results shed new light in the enzymatic activity of IDO2, and they support the view that this isoform of IDO also participates in the metabolism of Trp in vivo.
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Affiliation(s)
- Hajime J Yuasa
- Laboratory of Biochemistry, Department of Chemistry and Biotechnology, Faculty of Science and Technology, National University Corporation Kochi University, Japan
| | - Roland Stocker
- Arterial Inflammation and Redox Biology Group, Heart Research Institute, Newtown, NSW, Australia
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6
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Leone L, Chino M, Nastri F, Maglio O, Pavone V, Lombardi A. Mimochrome, a metalloporphyrin‐based catalytic Swiss knife†. Biotechnol Appl Biochem 2020; 67:495-515. [DOI: 10.1002/bab.1985] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 07/09/2020] [Indexed: 12/20/2022]
Affiliation(s)
- Linda Leone
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
| | - Marco Chino
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
| | - Flavia Nastri
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
| | - Ornella Maglio
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
- IBB ‐ National Research Council Napoli Italy
| | - Vincenzo Pavone
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
| | - Angela Lombardi
- Department of Chemical Sciences University of Napoli “Federico II” Napoli Italy
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7
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Cho D, Choi S, Cho J, Baik MH. Peroxocobalt(iii) species activates nitriles via a superoxocobalt(ii) diradical state. Dalton Trans 2020; 49:2819-2826. [PMID: 31960881 DOI: 10.1039/d0dt00042f] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dioxygenation of nitriles by [CoIII(TBDAP)(O2)]+ (TBDAP = N,N-di-tert-butyl-2,11-diaza[3.3](2,6)-pyridinophane) is investigated using DFT-calculations. The mechanism proposed previously based on experimental observations, which invoked an outer-sphere cycloaddition, was found to be unreasonable. Instead, calculations suggest that an inner-sphere mechanism involving the cleavage of one of the Co-O bonds assisted by substrate uptake is much more likely. The reactively competent species is a triplet consisting of a Co(ii)-superoxo functionality, which can undergo O-C bond formation and O-O bond cleavage traversing low energy transition states. The role of the structurally rigid TBDAP ligand is to prevent the participation of the pyridyl ligand in the delocalization of the unpaired electron density.
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Affiliation(s)
- Dasol Cho
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea. and Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Seulhui Choi
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea. and Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Jaeheung Cho
- Department of Emerging Materials Science, DGIST, Daegu 42988, Republic of Korea.
| | - Mu-Hyun Baik
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea. and Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
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8
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Wei Y, Lu C, Jiang S, Zhang Y, Li Q, Bai W, Wang X. Directed Evolution of a Tryptophan 2,3‐Dioxygenase for the Diastereoselective Monooxygenation of Tryptophans. Angew Chem Int Ed Engl 2020; 59:3043-3047. [DOI: 10.1002/anie.201911825] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 11/20/2019] [Indexed: 11/11/2022]
Affiliation(s)
- Yanxin Wei
- College of Bioscience and BiotechnologyYangzhou University Yangzhou Jiangsu 225009 China
| | - Chen Lu
- College of Bioscience and BiotechnologyYangzhou University Yangzhou Jiangsu 225009 China
| | - Shengsheng Jiang
- College of Bioscience and BiotechnologyYangzhou University Yangzhou Jiangsu 225009 China
| | - Yanyan Zhang
- Testing CenterYangzhou University Yangzhou Jiangsu 225009 China
| | - Qiuchun Li
- College of Bioscience and BiotechnologyYangzhou University Yangzhou Jiangsu 225009 China
| | - Wen‐Ju Bai
- Department of ChemistryStanford University Stanford California 94305 USA
- Present address: Amgen Inc. 1 Amgen Center Drive Thousand Oaks CA 91320 USA
| | - Xiqing Wang
- College of Bioscience and BiotechnologyYangzhou University Yangzhou Jiangsu 225009 China
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9
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Zhao R, Guo J, Zhang C, Lu Y, Dagnaw WM, Wang ZX. DFT Mechanistic Insight into the Dioxygenase-like Reactivity of a Co III-peroxo Complex: O–O Bond Cleavage via a [1,3]-Sigmatropic Rearrangement-like Mechanism. Inorg Chem 2020; 59:2051-2061. [DOI: 10.1021/acs.inorgchem.9b03470] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ruihua Zhao
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
| | - Jiandong Guo
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
| | - Chaoshen Zhang
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
| | - Yu Lu
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
| | - Wasihun Menberu Dagnaw
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
| | - Zhi-Xiang Wang
- School of Chemical Sciences, University of Chinese Academy of Sciences, Jia #19, Yuquan Road, Beijing 100039, China
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10
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Wei Y, Lu C, Jiang S, Zhang Y, Li Q, Bai W, Wang X. Directed Evolution of a Tryptophan 2,3‐Dioxygenase for the Diastereoselective Monooxygenation of Tryptophans. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201911825] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Yanxin Wei
- College of Bioscience and Biotechnology Yangzhou University Yangzhou Jiangsu 225009 China
| | - Chen Lu
- College of Bioscience and Biotechnology Yangzhou University Yangzhou Jiangsu 225009 China
| | - Shengsheng Jiang
- College of Bioscience and Biotechnology Yangzhou University Yangzhou Jiangsu 225009 China
| | - Yanyan Zhang
- Testing Center Yangzhou University Yangzhou Jiangsu 225009 China
| | - Qiuchun Li
- College of Bioscience and Biotechnology Yangzhou University Yangzhou Jiangsu 225009 China
| | - Wen‐Ju Bai
- Department of Chemistry Stanford University Stanford California 94305 USA
- Present address: Amgen Inc. 1 Amgen Center Drive Thousand Oaks CA 91320 USA
| | - Xiqing Wang
- College of Bioscience and Biotechnology Yangzhou University Yangzhou Jiangsu 225009 China
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11
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Lu X, Bai Y, Li Y, Shi Y, Li L, Wu Y, Zhong F. Assembly of C3a-Peroxylated Pyrroloindolines via Interrupted Witkop Oxidation. Org Lett 2018; 20:7937-7941. [DOI: 10.1021/acs.orglett.8b03509] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Xunbo Lu
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Yulong Bai
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Yan Li
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Yufeng Shi
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Longjie Li
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Yuzhou Wu
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
| | - Fangrui Zhong
- Hubei Key Laboratory of Bioinorganic Chemistry & Materia Medica, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan 430074, China
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12
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Guengerich FP, Yoshimoto FK. Formation and Cleavage of C-C Bonds by Enzymatic Oxidation-Reduction Reactions. Chem Rev 2018; 118:6573-6655. [PMID: 29932643 DOI: 10.1021/acs.chemrev.8b00031] [Citation(s) in RCA: 140] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Many oxidation-reduction (redox) enzymes, particularly oxygenases, have roles in reactions that make and break C-C bonds. The list includes cytochrome P450 and other heme-based monooxygenases, heme-based dioxygenases, nonheme iron mono- and dioxygenases, flavoproteins, radical S-adenosylmethionine enzymes, copper enzymes, and peroxidases. Reactions involve steroids, intermediary metabolism, secondary natural products, drugs, and industrial and agricultural chemicals. Many C-C bonds are formed via either (i) coupling of diradicals or (ii) generation of unstable products that rearrange. C-C cleavage reactions involve several themes: (i) rearrangement of unstable oxidized products produced by the enzymes, (ii) oxidation and collapse of radicals or cations via rearrangement, (iii) oxygenation to yield products that are readily hydrolyzed by other enzymes, and (iv) activation of O2 in systems in which the binding of a substrate facilitates O2 activation. Many of the enzymes involve metals, but of these, iron is clearly predominant.
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Affiliation(s)
- F Peter Guengerich
- Department of Biochemistry , Vanderbilt University School of Medicine , Nashville , Tennessee 37232-0146 , United States.,Department of Chemistry , University of Texas-San Antonio , San Antonio , Texas 78249-0698 , United States
| | - Francis K Yoshimoto
- Department of Biochemistry , Vanderbilt University School of Medicine , Nashville , Tennessee 37232-0146 , United States.,Department of Chemistry , University of Texas-San Antonio , San Antonio , Texas 78249-0698 , United States
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13
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Abstract
Iron-containing enzymes such as heme enzymes play crucial roles in biological systems. Three distinct heme-containing dioxygenase enzymes, tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 1 (IDO1) and indoleamine 2,3-dioxygenase 2 (IDO2) catalyze the initial and rate-limiting step of l-tryptophan catabolism through the kynurenine pathway in mammals. Overexpression of these enzymes causes depletion of tryptophan and the accumulation of metabolic products, which contributes to tumor immune tolerance and immune dysregulation in a variety of disease pathologies. In the past few decades, IDO1 has garnered the most attention as a therapeutic target with great potential in cancer immunotherapy. Many potential inhibitors of IDO1 have been designed, synthesized and evaluated, among which indoximod (d-1-MT), INCB024360, GDC-0919 (formerly NLG-919), and an IDO1 peptide-based vaccine have advanced to the clinical trial stage. However, recently, the roles of TDO and IDO2 have been elucidated in immune suppression. In this review, the current drug discovery landscape for targeting TDO, IDO1 and IDO2 is highlighted, with particular attention to the recent use of drugs in clinical trials. Moreover, the crystal structures of these enzymes, in complex with inhibitors, and the mechanisms of Trp catabolism in the first step, are summarized to provide information for facilitating the discovery of new enzyme inhibitors.
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Affiliation(s)
- Daojing Yan
- Department of Chemistry & Institutes of Biomedical Sciences, Fudan University, Shanghai 200433, China.
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14
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Huang X, Groves JT. Oxygen Activation and Radical Transformations in Heme Proteins and Metalloporphyrins. Chem Rev 2018; 118:2491-2553. [PMID: 29286645 PMCID: PMC5855008 DOI: 10.1021/acs.chemrev.7b00373] [Citation(s) in RCA: 579] [Impact Index Per Article: 96.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Indexed: 12/20/2022]
Abstract
As a result of the adaptation of life to an aerobic environment, nature has evolved a panoply of metalloproteins for oxidative metabolism and protection against reactive oxygen species. Despite the diverse structures and functions of these proteins, they share common mechanistic grounds. An open-shell transition metal like iron or copper is employed to interact with O2 and its derived intermediates such as hydrogen peroxide to afford a variety of metal-oxygen intermediates. These reactive intermediates, including metal-superoxo, -(hydro)peroxo, and high-valent metal-oxo species, are the basis for the various biological functions of O2-utilizing metalloproteins. Collectively, these processes are called oxygen activation. Much of our understanding of the reactivity of these reactive intermediates has come from the study of heme-containing proteins and related metalloporphyrin compounds. These studies not only have deepened our understanding of various functions of heme proteins, such as O2 storage and transport, degradation of reactive oxygen species, redox signaling, and biological oxygenation, etc., but also have driven the development of bioinorganic chemistry and biomimetic catalysis. In this review, we survey the range of O2 activation processes mediated by heme proteins and model compounds with a focus on recent progress in the characterization and reactivity of important iron-oxygen intermediates. Representative reactions initiated by these reactive intermediates as well as some context from prior decades will also be presented. We will discuss the fundamental mechanistic features of these transformations and delineate the underlying structural and electronic factors that contribute to the spectrum of reactivities that has been observed in nature as well as those that have been invented using these paradigms. Given the recent developments in biocatalysis for non-natural chemistries and the renaissance of radical chemistry in organic synthesis, we envision that new enzymatic and synthetic transformations will emerge based on the radical processes mediated by metalloproteins and their synthetic analogs.
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Affiliation(s)
- Xiongyi Huang
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department
of Chemistry, California Institute of Technology, Pasadena, California 91125, United States
| | - John T. Groves
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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15
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Abstract
Aerobic organisms have evolved to activate oxygen from the atmosphere, which allows them to catalyze the oxidation of different kinds of substrates. This activation of oxygen is achieved by a metal center (usually iron or copper) buried within a metalloprotein. In the case of iron-containing heme enzymes, the activation of oxygen is achieved by formation of transient iron-oxo (ferryl) intermediates; these intermediates are called Compound I and Compound II. The Compound I and II intermediates were first discovered in the 1930s in horseradish peroxidase, and it is now known that these same species are used across the family of heme enzymes, which include all of the peroxidases, the heme catalases, the P450s, cytochrome c oxidase, and NO synthase. Many years have passed since the first observations, but establishing the chemical nature of these transient ferryl species remains a fundamental question that is relevant to the reactivity, and therefore the usefulness, of these species in biology. This Account summarizes experiments that were conceived and conducted at Leicester and presents our ideas on the chemical nature, stability, and reactivity of these ferryl heme species. We begin by briefly summarizing the early milestones in the field, from the 1940s and 1950s. We present comparisons between the nature and reactivity of the ferryl species in horseradish peroxidase, cytochrome c peroxidase, and ascorbate peroxidase; and we consider different modes of electron delivery to ferryl heme, from different substrates in different peroxidases. We address the question of whether the ferryl heme is best formulated as an (unprotonated) FeIV═O or as a (protonated) FeIV-OH species. A range of spectroscopic approaches (EXAFS, resonance Raman, Mossbauer, and EPR) have been used over many decades to examine this question, and in the last ten years, X-ray crystallography has also been employed. We describe how information from all of these studies has blended together to create an overall picture, and how the recent application of neutron crystallography has directly identified protonation states and has helped to clarify the precise nature of the ferryl heme in cytochrome c peroxidase and ascorbate peroxidase. We draw comparisons between the Compound I and Compound II species that we have observed in peroxidases with those found in other heme systems, notably the P450s, highlighting possible commonality across these heme ferryl systems. The identification of proton locations from neutron structures of these ferryl species opens the door for understanding the proton translocations that need to occur during O-O bond cleavage.
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Affiliation(s)
- Peter C. E. Moody
- Department
of Molecular and Cell Biology and Leicester Institute of Structural
and Chemical Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Emma L. Raven
- Department
of Chemistry and Leicester Institute of Structural and Chemical Biology, University of Leicester, University Road, Leicester LE1 7RH, U.K
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16
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Nienhaus K, Nienhaus GU. Different Mechanisms of Catalytic Complex Formation in Two L-Tryptophan Processing Dioxygenases. Front Mol Biosci 2018; 4:94. [PMID: 29354636 PMCID: PMC5758539 DOI: 10.3389/fmolb.2017.00094] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 12/18/2017] [Indexed: 01/25/2023] Open
Abstract
The human heme enzymes tryptophan 2,3-dioxygenase (hTDO) and indoleamine 2,3 dioxygenase (hIDO) catalyze the initial step in L-tryptophan (L-Trp) catabolism, the insertion of dioxygen into L-Trp. Overexpression of these enzymes causes depletion of L-Trp and accumulation of metabolic products, and thereby contributes to tumor immune tolerance and immune dysregulation in a variety of disease pathologies. Understanding the assembly of the catalytically active, ternary enzyme-substrate-ligand complexes is not yet fully resolved, but an essential prerequisite for designing efficient and selective de novo inhibitors. Evidence is mounting that the ternary complex forms by sequential binding of ligand and substrate in a specific order. In hTDO, the apolar L-Trp binds first, decreasing active-site solvation and, as a result, reducing non-productive oxidation of the heme iron by the dioxygen ligand, which may leave the substrate bound to a ferric heme iron. In hIDO, by contrast, dioxygen must first coordinate to the heme iron because a bound substrate would occlude ligand access to the heme iron, so the ternary complex can no longer form. Consequently, faster association of L-Trp at high concentrations results in substrate inhibition. Here, we summarize our present knowledge of ternary complex formation in hTDO and hIDO and relate these findings to structural peculiarities of their active sites.
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Affiliation(s)
- Karin Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany
| | - G Ulrich Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany.,Institute of Nanotechnology and Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.,Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, United States
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17
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Mahida AK, Kale SB, Das U. Synthesis Route to Pyrrolones from α-Cyano α,β-Unsaturated Ketones and α-Isocyano Esters by Oxidative Dearomatization of 2-Aminofuran Intermediates. European J Org Chem 2017. [DOI: 10.1002/ejoc.201701194] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Anil K. Mahida
- Division of Organic Chemistry; CSIR - National Chemical Laboratory; 411008 Pune India
- Academy of Scientific and Innovative Research (AcSIR); 110020 New Delhi India
| | - Someshwar B. Kale
- Division of Organic Chemistry; CSIR - National Chemical Laboratory; 411008 Pune India
- Academy of Scientific and Innovative Research (AcSIR); 110020 New Delhi India
| | - Utpal Das
- Division of Organic Chemistry; CSIR - National Chemical Laboratory; 411008 Pune India
- Academy of Scientific and Innovative Research (AcSIR); 110020 New Delhi India
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18
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Nienhaus K, Hahn V, Hüpfel M, Nienhaus GU. Substrate Binding Primes Human Tryptophan 2,3-Dioxygenase for Ligand Binding. J Phys Chem B 2017; 121:7412-7420. [PMID: 28715185 DOI: 10.1021/acs.jpcb.7b03463] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The human heme enzyme tryptophan 2,3-dioxygenase (hTDO) catalyzes the insertion of dioxygen into its cognate substrate, l-tryptophan (l-Trp). Its active site structure is highly dynamic, and the mechanism of enzyme-substrate-ligand complex formation and the ensuing enzymatic reaction is not yet understood. Here we have studied complex formation in hTDO by using time-resolved optical and infrared spectroscopy with carbon monoxide (CO) as a ligand. We have observed that both substrate-free and substrate-bound hTDO coexist in two discrete conformations with greatly different ligand binding rates. In the fast rebinding hTDO conformation, there is facile ligand access to the heme iron, but it is greatly hindered in the slowly rebinding conformation. Spectroscopic evidence implicates active site solvation as playing a crucial role for the observed kinetic differences. Substrate binding shifts the conformational equilibrium markedly toward the fast species and thus primes the active site for subsequent ligand binding, ensuring that formation of the ternary complex occurs predominantly by first binding l-Trp and then the ligand. Consequently, the efficiency of catalysis is enhanced because O2 binding prior to substrate binding, resulting in nonproductive oxidation of the heme iron, is greatly suppressed.
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Affiliation(s)
- Karin Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Vincent Hahn
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Manuel Hüpfel
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - G Ulrich Nienhaus
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany.,Institute of Nanotechnology (INT) and Institute of Toxicology and Genetics (ITG), Karlsruhe Institute of Technology (KIT) , 76344 Eggenstein-Leopoldshafen, Germany.,Department of Physics, University of Illinois at Urbana-Champaign , 1110 W. Green Street, Urbana, Illinois 61801, United States
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19
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Nienhaus K, Nickel E, Nienhaus GU. Substrate binding in human indoleamine 2,3-dioxygenase 1: A spectroscopic analysis. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:453-463. [DOI: 10.1016/j.bbapap.2017.02.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Revised: 01/22/2017] [Accepted: 02/07/2017] [Indexed: 11/27/2022]
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20
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Klare HFT, Goldberg AFG, Duquette DC, Stoltz BM. Oxidative Fragmentations and Skeletal Rearrangements of Oxindole Derivatives. Org Lett 2017; 19:988-991. [DOI: 10.1021/acs.orglett.6b03789] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hendrik F. T. Klare
- The Warren and Katharine
Schlinger Laboratory for Chemistry and Chemical Engineering, Division
of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Alexander F. G. Goldberg
- The Warren and Katharine
Schlinger Laboratory for Chemistry and Chemical Engineering, Division
of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Douglas C. Duquette
- The Warren and Katharine
Schlinger Laboratory for Chemistry and Chemical Engineering, Division
of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Brian M. Stoltz
- The Warren and Katharine
Schlinger Laboratory for Chemistry and Chemical Engineering, Division
of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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21
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Basran J, Booth ES, Lee M, Handa S, Raven EL. Analysis of Reaction Intermediates in Tryptophan 2,3-Dioxygenase: A Comparison with Indoleamine 2,3-Dioxygenase. Biochemistry 2016; 55:6743-6750. [PMID: 27951658 DOI: 10.1021/acs.biochem.6b01005] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) are heme-containing enzymes that catalyze the O2-dependent oxidation of l-tryptophan (l-Trp) in biological systems. Although many decades have passed since their discovery, the mechanism of tryptophan oxidation has not been established. It has been widely assumed that IDO and TDO react using the same mechanism, although there is no evidence that they do. For IDO, a Compound II (ferryl) species accumulates in the steady state and is implicated in the mechanism; in TDO, no such species has ever been observed. In this paper, we examine the kinetics of tryptophan oxidation in TDO. We find no evidence for the accumulation of Compound II during TDO catalysis. Instead, a ternary [Fe(II)-O2, l-Trp] complex is detected under steady state conditions. The absence of a Compound II species in the steady state in TDO is not due to an intrinsic inability of the TDO enzyme to form ferryl heme, because Compound II can be formed directly through a different route in which ferrous heme is reacted with peroxide. We interpret the data to mean that the rate-limiting step in the IDO and TDO mechanisms is not the same.
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Affiliation(s)
- Jaswir Basran
- Department of Molecular and Cellular Biology and Henry Wellcome Laboratories for Structural Biology, Henry Wellcome Building, University of Leicester , Lancaster Road, Leicester LE1 7RH, England, U.K
| | - Elizabeth S Booth
- Department of Chemistry, University of Leicester , University Road, Leicester LE1 7RH, England, U.K
| | - Michael Lee
- Department of Molecular and Cellular Biology and Henry Wellcome Laboratories for Structural Biology, Henry Wellcome Building, University of Leicester , Lancaster Road, Leicester LE1 7RH, England, U.K
| | - Sandeep Handa
- Department of Chemistry, University of Leicester , University Road, Leicester LE1 7RH, England, U.K
| | - Emma L Raven
- Department of Chemistry, University of Leicester , University Road, Leicester LE1 7RH, England, U.K
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22
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Raven EL. A short history of heme dioxygenases: rise, fall and rise again. J Biol Inorg Chem 2016; 22:175-183. [PMID: 27909919 PMCID: PMC5350241 DOI: 10.1007/s00775-016-1412-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 11/10/2016] [Indexed: 01/20/2023]
Abstract
It is well established that there are two different classes of enzymes—tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO)—that catalyse the O2-dependent oxidation of l-tryptophan to N-formylkynurenine. But it was not always so. This perspective presents a short history of the early TDO and IDO literature, the people that were involved in creating it, and the legacy that this left for the future.
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Affiliation(s)
- Emma L Raven
- Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK.
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23
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Kumar Y, Jaiswal Y, Kumar A. Copper(II)-Catalyzed Benzylic C(sp3)–H Aerobic Oxidation of (Hetero)Aryl Acetimidates: Synthesis of Aryl-α-ketoesters. J Org Chem 2016; 81:12247-12257. [DOI: 10.1021/acs.joc.6b02176] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Yogesh Kumar
- Department of Chemistry, Indian Institute of Technology Patna, Bihta 801103, Bihar, India
| | - Yogesh Jaiswal
- Department of Chemistry, Indian Institute of Technology Patna, Bihta 801103, Bihar, India
| | - Amit Kumar
- Department of Chemistry, Indian Institute of Technology Patna, Bihta 801103, Bihar, India
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24
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Unique coupling of mono- and dioxygenase chemistries in a single active site promotes heme degradation. Proc Natl Acad Sci U S A 2016; 113:3779-84. [PMID: 27006503 DOI: 10.1073/pnas.1523333113] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bacterial pathogens must acquire host iron for survival and colonization. Because free iron is restricted in the host, numerous pathogens have evolved to overcome this limitation by using a family of monooxygenases that mediate the oxidative cleavage of heme into biliverdin, carbon monoxide, and iron. However, the etiological agent of tuberculosis, Mycobacterium tuberculosis, accomplishes this task without generating carbon monoxide, which potentially induces its latent state. Here we show that this unusual heme degradation reaction proceeds through sequential mono- and dioxygenation events within the single active center of MhuD, a mechanism unparalleled in enzyme catalysis. A key intermediate of the MhuD reaction is found to be meso-hydroxyheme, which reacts with O2 at an unusual position to completely suppress its monooxygenation but to allow ring cleavage through dioxygenation. This mechanistic change, possibly due to heavy steric deformation of hydroxyheme, rationally explains the unique heme catabolites of MhuD. Coexistence of mechanistically distinct functions is a previously unidentified strategy to expand the physiological outcome of enzymes, and may be applied to engineer unique biocatalysts.
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25
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Booth ES, Basran J, Lee M, Handa S, Raven EL. Substrate Oxidation by Indoleamine 2,3-Dioxygenase: EVIDENCE FOR A COMMON REACTION MECHANISM. J Biol Chem 2015; 290:30924-30. [PMID: 26511316 PMCID: PMC4692220 DOI: 10.1074/jbc.m115.695684] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Indexed: 11/06/2022] Open
Abstract
The kynurenine pathway is the major route of l-tryptophan (l-Trp) catabolism in biology, leading ultimately to the formation of NAD+. The initial and rate-limiting step of the kynurenine pathway involves oxidation of l-Trp to N-formylkynurenine. This is an O2-dependent process and catalyzed by indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase. More than 60 years after these dioxygenase enzymes were first isolated (Kotake, Y., and Masayama, I. (1936) Z. Physiol. Chem. 243, 237–244), the mechanism of the reaction is not established. We examined the mechanism of substrate oxidation for a series of substituted tryptophan analogues by indoleamine 2,3-dioxygenase. We observed formation of a transient intermediate, assigned as a Compound II (ferryl) species, during oxidation of l-Trp, 1-methyl-l-Trp, and a number of other substrate analogues. The data are consistent with a common reaction mechanism for indoleamine 2,3-dioxygenase-catalyzed oxidation of tryptophan and other tryptophan analogues.
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Affiliation(s)
- Elizabeth S Booth
- From the Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, Great Britain, United Kingdom and
| | - Jaswir Basran
- Department of Molecular and Cellular Biology and Henry Wellcome Laboratories for Structural Biology, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, Great Britain, United Kingdom
| | - Michael Lee
- From the Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, Great Britain, United Kingdom and
| | - Sandeep Handa
- From the Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, Great Britain, United Kingdom and
| | - Emma L Raven
- From the Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, Great Britain, United Kingdom and
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26
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Abstract
IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.
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27
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Geng J, Liu A. Heme-dependent dioxygenases in tryptophan oxidation. Arch Biochem Biophys 2013; 544:18-26. [PMID: 24295960 DOI: 10.1016/j.abb.2013.11.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 11/19/2013] [Accepted: 11/20/2013] [Indexed: 12/29/2022]
Abstract
L-Tryptophan is an essential amino acid for mammals. It is utilized not only for protein synthesis but also for the biosynthesis of serotonin and melatonin by the serotonin pathway as well as nicotinamide adenine dinucleotide by the kynurenine pathway. Although the kynurenine pathway is responsible for the catabolism of over 90% of l-tryptophan in the mammalian intracellular and extracellular pools, the scientific field was dominated in the last century by studies of the serotonin pathway, due to the physiological significance of the latter's catabolic intermediates and products. However, in the past decade, the focus gradually reversed as the link between the kynurenine pathway and various neurodegenerative disorders and immune diseases is increasingly highlighted. Notably, the first step of this pathway, which is catalyzed by heme-dependent dioxygenases, has been proven to be a potential target for immune regulation and cancer treatment. A thorough understanding of the intriguing chemistry of the heme-dependent dioxygenases may yield insight for the drug discovery of these prevalent illnesses. In this review, we survey enzymatic and mechanistic studies, initially started by Kotake and Masayama over 70 years ago, at the molecular level on the heme-dependent tryptophan dioxygenation reactions.
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Affiliation(s)
- Jiafeng Geng
- Department of Chemistry, Georgia State University, 50 Decatur Street SE, Atlanta, GA 30303, United States
| | - Aimin Liu
- Department of Chemistry, Georgia State University, 50 Decatur Street SE, Atlanta, GA 30303, United States.
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28
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Chauhan N, Basran J, Rafice SA, Efimov I, Millett ES, Mowat CG, Moody PCE, Handa S, Raven EL. How is the distal pocket of a heme protein optimized for binding of tryptophan? FEBS J 2012; 279:4501-9. [DOI: 10.1111/febs.12036] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 10/15/2012] [Accepted: 10/16/2012] [Indexed: 12/30/2022]
Affiliation(s)
- Nishma Chauhan
- Department of Chemistry; Henry Wellcome Building; University of Leicester; UK
| | - Jaswir Basran
- Department of Biochemistry; Henry Wellcome Building; University of Leicester; UK
| | - Sara A. Rafice
- Department of Chemistry; Henry Wellcome Building; University of Leicester; UK
| | - Igor Efimov
- Department of Chemistry; Henry Wellcome Building; University of Leicester; UK
| | | | | | | | - Sandeep Handa
- Department of Chemistry; Henry Wellcome Building; University of Leicester; UK
| | - Emma L. Raven
- Department of Chemistry; Henry Wellcome Building; University of Leicester; UK
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