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Baljinnyam T, Sowers ML, Hsu CW, Conrad JW, Herring JL, Hackfeld LC, Sowers LC. Chemical and enzymatic modifications of 5-methylcytosine at the intersection of DNA damage, repair, and epigenetic reprogramming. PLoS One 2022; 17:e0273509. [PMID: 36037209 PMCID: PMC9423628 DOI: 10.1371/journal.pone.0273509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 08/09/2022] [Indexed: 11/19/2022] Open
Abstract
The DNA of all living organisms is persistently damaged by endogenous reactions including deamination and oxidation. Such damage, if not repaired correctly, can result in mutations that drive tumor development. In addition to chemical damage, recent studies have established that DNA bases can be enzymatically modified, generating many of the same modified bases. Irrespective of the mechanism of formation, modified bases can alter DNA-protein interactions and therefore modulate epigenetic control of gene transcription. The simultaneous presence of both chemically and enzymatically modified bases in DNA suggests a potential intersection, or collision, between DNA repair and epigenetic reprogramming. In this paper, we have prepared defined sequence oligonucleotides containing the complete set of oxidized and deaminated bases that could arise from 5-methylcytosine. We have probed these substrates with human glycosylases implicated in DNA repair and epigenetic reprogramming. New observations reported here include: SMUG1 excises 5-carboxyuracil (5caU) when paired with A or G. Both TDG and MBD4 cleave 5-formyluracil and 5caU when mispaired with G. Further, TDG not only removes 5-formylcytosine and 5-carboxycytosine when paired with G, but also when mispaired with A. Surprisingly, 5caU is one of the best substrates for human TDG, SMUG1 and MBD4, and a much better substrate than T. The data presented here introduces some unexpected findings that pose new questions on the interactions between endogenous DNA damage, repair, and epigenetic reprogramming pathways.
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Affiliation(s)
- Tuvshintugs Baljinnyam
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Mark L. Sowers
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
- MD-PhD Combined Degree Program, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Chia Wei Hsu
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
- MD-PhD Combined Degree Program, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - James W. Conrad
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Jason L. Herring
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Linda C. Hackfeld
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Lawrence C. Sowers
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas, United States of America
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, United States of America
- * E-mail:
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Structure and Function of TET Enzymes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1389:239-267. [DOI: 10.1007/978-3-031-11454-0_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Aparici-Espert I, Garcia-Lainez G, Andreu I, Miranda MA, Lhiaubet-Vallet V. Oxidatively Generated Lesions as Internal Photosensitizers for Pyrimidine Dimerization in DNA. ACS Chem Biol 2018; 13:542-547. [PMID: 29300457 DOI: 10.1021/acschembio.7b01097] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In this work, the attention is focused on UVA-photosensitized reactions triggered by a DNA chromophore-containing lesion, namely 5-formyluracil. This is a major oxidatively generated lesion that exhibits an enhanced light absorption in the UVB-UVA region. The mechanistic study combining photochemical and photobiological techniques shows that irradiation of 5-formyluracil leads to a triplet excited state capable of sensitizing formation of cyclobutane pyrimidine dimers in DNA via a triplet-triplet energy transfer. This demonstrates for the first time that oxidatively generated DNA damage can behave as an intrinsic sensitizer and result in an important extension of the active fraction of the solar spectrum with photocarcinogenic potential. Overall, this raises the question of an aggravated photomutagenicity of the 5-formyluracil lesion.
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Affiliation(s)
- Isabel Aparici-Espert
- Instituto Universitario Mixto de Tecnología Química (UPV-CSIC), Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos, s/n, 46022, Valencia (Spain)
| | - Guillermo Garcia-Lainez
- Instituto de Investigación Sanitaria La Fe, Hospital Universitari i Politècnic La Fe, Avenida de Fernando Abril Martorell 106, 46026 Valencia (Spain)
| | - Inmaculada Andreu
- Instituto de Investigación Sanitaria La Fe, Hospital Universitari i Politècnic La Fe, Avenida de Fernando Abril Martorell 106, 46026 Valencia (Spain)
| | - Miguel Angel Miranda
- Instituto Universitario Mixto de Tecnología Química (UPV-CSIC), Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos, s/n, 46022, Valencia (Spain)
| | - Virginie Lhiaubet-Vallet
- Instituto Universitario Mixto de Tecnología Química (UPV-CSIC), Universitat Politècnica de València, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos, s/n, 46022, Valencia (Spain)
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Yin X, Xu Y. Structure and Function of TET Enzymes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 945:275-302. [PMID: 27826843 DOI: 10.1007/978-3-319-43624-1_12] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Mammalian DNA methylation mainly occurs at the carbon-C5 position of cytosine (5mC). TET enzymes were discovered to successively oxidize 5mC to 5-hydromethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). TET enzymes and oxidized 5mC derivatives play important roles in various biological and pathological processes, including regulation of DNA demethylation, gene transcription, embryonic development, and oncogenesis. In this chapter, we will discuss the discovery of TET-mediated 5mC oxidation and the structure, function, and regulation of TET enzymes.
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Affiliation(s)
- Xiaotong Yin
- Fudan University Shanghai Cancer Center, Institute of Biomedical Sciences, Shanghai Medical College of Fudan University, Shanghai, 200032, China
| | - Yanhui Xu
- Fudan University Shanghai Cancer Center, Institute of Biomedical Sciences, Shanghai Medical College of Fudan University, Shanghai, 200032, China.
- Key Laboratory of Molecular Medicine, Ministry of Education, Department of Systems Biology for Medicine, School of Basic Medical Sciences, Shanghai Medical College of Fudan University, Shanghai, 200032, China.
- State Key Laboratory of Genetic Engineering, Collaborative Innovation Center of Genetics and Development, School of Life Sciences, Fudan University, Shanghai, 200433, China.
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Li W, Zhang T, Ding J. Molecular basis for the substrate specificity and catalytic mechanism of thymine-7-hydroxylase in fungi. Nucleic Acids Res 2015; 43:10026-38. [PMID: 26429971 PMCID: PMC4787775 DOI: 10.1093/nar/gkv979] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 09/18/2015] [Indexed: 12/17/2022] Open
Abstract
TET proteins play a vital role in active DNA demethylation in mammals and thus have important functions in many essential cellular processes. The chemistry for the conversion of 5mC to 5hmC, 5fC and 5caC catalysed by TET proteins is similar to that of T to 5hmU, 5fU and 5caU catalysed by thymine-7-hydroxylase (T7H) in the nucleotide anabolism in fungi. Here, we report the crystal structures and biochemical properties of Neurospora crassa T7H. T7H can bind the substrates only in the presence of cosubstrate, and binding of different substrates does not induce notable conformational changes. T7H exhibits comparable binding affinity for T and 5hmU, but 3-fold lower affinity for 5fU. Residues Phe292, Tyr217 and Arg190 play critical roles in substrate binding and catalysis, and the interactions of the C5 modification group of substrates with the cosubstrate and enzyme contribute to the slightly varied binding affinity and activity towards different substrates. After the catalysis, the products are released and new cosubstrate and substrate are reloaded to conduct the next oxidation reaction. Our data reveal the molecular basis for substrate specificity and catalytic mechanism of T7H and provide new insights into the molecular mechanism of substrate recognition and catalysis of TET proteins.
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Affiliation(s)
- Wenjing Li
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Tianlong Zhang
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Jianping Ding
- National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China Collaborative Innovation Center for Genetics and Development, Fudan University, 2005 Song-Hu Road, Shanghai 200438, China
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Hernández-Almanza A, Cesar Montanez J, Aguilar-González MA, Martínez-Ávila C, Rodríguez-Herrera R, Aguilar CN. Rhodotorula glutinis as source of pigments and metabolites for food industry. FOOD BIOSCI 2014. [DOI: 10.1016/j.fbio.2013.11.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Cadet J, Wagner JR. TET enzymatic oxidation of 5-methylcytosine, 5-hydroxymethylcytosine and 5-formylcytosine. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2013; 764-765:18-35. [PMID: 24045206 DOI: 10.1016/j.mrgentox.2013.09.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Accepted: 09/04/2013] [Indexed: 12/14/2022]
Abstract
5-Methylcytosine and methylated histones have been considered for a long time as stable epigenetic marks of chromatin involved in gene regulation. This concept has been recently revisited with the detection of large amounts of 5-hydroxymethylcytosine, now considered as the sixth DNA base, in mouse embryonic stem cells, Purkinje neurons and brain tissues. The dioxygenases that belong to the ten eleven translocation (TET) oxygenase family have been shown to initiate the formation of this methyl oxidation product of 5-methylcytosine that is also generated although far less efficiently by radical reactions involving hydroxyl radical and one-electron oxidants. It was found as additional striking data that iterative TET-mediated oxidation of 5-hydroxymethylcytosine gives rise to 5-formylcytosine and 5-carboxylcytosine. This survey focuses on chemical and biochemical aspects of the enzymatic oxidation reactions of 5-methylcytosine that are likely to be involved in active demethylation pathways through the implication of enzymatic deamination of 5-methylcytosine oxidation products and/or several base excision repair enzymes. The high biological relevance of the latter modified bases explains why major efforts have been devoted to the design of a broad range of assays aimed at measuring globally or at the single base resolution, 5-hydroxymethylcytosine and the two other oxidation products in the DNA of cells and tissues. Another critical issue that is addressed in this review article deals with the assessment of the possible role of 5-methylcytosine oxidation products, when present in elevated amounts in cellular DNA, in terms of mutagenesis and interference with key cellular enzymes including DNA and RNA polymerases.
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Affiliation(s)
- Jean Cadet
- Direction des Sciences de la Matière, Institut Nanosciences et Cryogénie, CEA/Grenoble, 38054 Grenoble, France; Département de médecine nucléaire et radiobiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Québec JIH 5N4, Canada.
| | - J Richard Wagner
- Département de médecine nucléaire et radiobiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Québec JIH 5N4, Canada.
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Abstract
Epigenetic genome marking and chromatin regulation are central to establishing tissue-specific gene expression programs, and hence to several biological processes. Until recently, the only known epigenetic mark on DNA in mammals was 5-methylcytosine, established and propagated by DNA methyltransferases and generally associated with gene repression. All of a sudden, a host of new actors—novel cytosine modifications and the ten eleven translocation (TET) enzymes—has appeared on the scene, sparking great interest. The challenge is now to uncover the roles they play and how they relate to DNA demethylation. Knowledge is accumulating at a frantic pace, linking these new players to essential biological processes (e.g. cell pluripotency and development) and also to cancerogenesis. Here, we review the recent progress in this exciting field, highlighting the TET enzymes as epigenetic DNA modifiers, their physiological roles, and their functions in health and disease. We also discuss the need to find relevant TET interactants and the newly discovered TET–O-linked N-acetylglucosamine transferase (OGT) pathway.
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Kundu S. Distribution and prediction of catalytic domains in 2-oxoglutarate dependent dioxygenases. BMC Res Notes 2012; 5:410. [PMID: 22862831 PMCID: PMC3475032 DOI: 10.1186/1756-0500-5-410] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 06/29/2012] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND The 2-oxoglutarate dependent superfamily is a diverse group of non-haem dioxygenases, and is present in prokaryotes, eukaryotes, and archaea. The enzymes differ in substrate preference and reaction chemistry, a factor that precludes their classification by homology studies and electronic annotation schemes alone. In this work, I propose and explore the rationale of using substrates to classify structurally similar alpha-ketoglutarate dependent enzymes. FINDINGS Differential catalysis in phylogenetic clades of 2-OG dependent enzymes, is determined by the interactions of a subset of active-site amino acids. Identifying these with existing computational methods is challenging and not feasible for all proteins. A clustering protocol based on validated mechanisms of catalysis of known molecules, in tandem with group specific hidden markov model profiles is able to differentiate and sequester these enzymes. Access to this repository is by a web server that compares user defined unknown sequences to these pre-defined profiles and outputs a list of predicted catalytic domains. The server is free and is accessible at the following URL (http://comp-biol.theacms.in/H2OGpred.html). CONCLUSIONS The proposed stratification is a novel attempt at classifying and predicting 2-oxoglutarate dependent function. In addition, the server will provide researchers with a tool to compare their data to a comprehensive list of HMM profiles of catalytic domains. This work, will aid efforts by investigators to screen and characterize putative 2-OG dependent sequences. The profile database will be updated at regular intervals.
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Affiliation(s)
- Siddhartha Kundu
- Department of Biochemistry, Army College of Medical Sciences, Delhi Cantt., New Delhi 110010, India.
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10
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Wu H, Zhang Y. Mechanisms and functions of Tet protein-mediated 5-methylcytosine oxidation. Genes Dev 2012; 25:2436-52. [PMID: 22156206 DOI: 10.1101/gad.179184.111] [Citation(s) in RCA: 480] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Ten-eleven translocation 1-3 (Tet1-3) proteins have recently been discovered in mammalian cells to be members of a family of DNA hydroxylases that possess enzymatic activity toward the methyl mark on the 5-position of cytosine (5-methylcytosine [5mC]), a well-characterized epigenetic modification that has essential roles in regulating gene expression and maintaining cellular identity. Tet proteins can convert 5mC into 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) through three consecutive oxidation reactions. These modified bases may represent new epigenetic states in genomic DNA or intermediates in the process of DNA demethylation. Emerging biochemical, genetic, and functional evidence suggests that Tet proteins are crucial for diverse biological processes, including zygotic epigenetic reprogramming, pluripotent stem cell differentiation, hematopoiesis, and development of leukemia. Insights into how Tet proteins contribute to dynamic changes in DNA methylation and gene expression will greatly enhance our understanding of epigenetic regulation of normal development and human diseases.
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Affiliation(s)
- Hao Wu
- Howard Hughes Medical Institute
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11
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Abstract
Methylation of DNA and histones in chromatin has been implicated in numerous biological processes. For many years, methylation has been recognized as static and stable modification, as compared with other covalent modifications of chromatin. Recently, however, several mechanisms have been demonstrated to be involved in demethylation of chromatin, suggesting that chromatin methylation is more dynamically regulated. One chemical reaction that mediates demethylation of both DNA and histones is hydroxylation, catalysed by Fe(II) and α-ketoglutarate (KG)-dependent hydroxylase/dioxygenase. Given that methylation of chromatin is an important epigenetic mark involved in fundamental biological processes such as cell fate determination, understanding how chromatin methylation is dynamically regulated has implications for human diseases and regenerative medicine.
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Affiliation(s)
- Yu-ichi Tsukada
- Division of Molecular Immunology, Research Center for Infectious Diseases, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan.
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Ito S, Shen L, Dai Q, Wu SC, Collins LB, Swenberg JA, He C, Zhang Y. Tet proteins can convert 5-methylcytosine to 5-formylcytosine and 5-carboxylcytosine. Science 2011; 333:1300-3. [PMID: 21778364 PMCID: PMC3495246 DOI: 10.1126/science.1210597] [Citation(s) in RCA: 2497] [Impact Index Per Article: 192.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
5-methylcytosine (5mC) in DNA plays an important role in gene expression, genomic imprinting, and suppression of transposable elements. 5mC can be converted to 5-hydroxymethylcytosine (5hmC) by the Tet (ten eleven translocation) proteins. Here, we show that, in addition to 5hmC, the Tet proteins can generate 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) from 5mC in an enzymatic activity-dependent manner. Furthermore, we reveal the presence of 5fC and 5caC in genomic DNA of mouse embryonic stem cells and mouse organs. The genomic content of 5hmC, 5fC, and 5caC can be increased or reduced through overexpression or depletion of Tet proteins. Thus, we identify two previously unknown cytosine derivatives in genomic DNA as the products of Tet proteins. Our study raises the possibility that DNA demethylation may occur through Tet-catalyzed oxidation followed by decarboxylation.
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Affiliation(s)
- Shinsuke Ito
- Howard Hughes Medical Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
| | - Li Shen
- Howard Hughes Medical Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
| | - Qing Dai
- Department of Chemistry and Institute for Biophysical Dynamics, the University of Chicago, Chicago, Illinois, USA
| | - Susan C. Wu
- Howard Hughes Medical Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
| | - Leonard B. Collins
- Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
| | - James A. Swenberg
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
| | - Chuan He
- Department of Chemistry and Institute for Biophysical Dynamics, the University of Chicago, Chicago, Illinois, USA
| | - Yi Zhang
- Howard Hughes Medical Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295
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Maiti A, Drohat AC. Thymine DNA glycosylase can rapidly excise 5-formylcytosine and 5-carboxylcytosine: potential implications for active demethylation of CpG sites. J Biol Chem 2011; 286:35334-35338. [PMID: 21862836 DOI: 10.1074/jbc.c111.284620] [Citation(s) in RCA: 631] [Impact Index Per Article: 48.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Thymine DNA glycosylase (TDG) excises T from G·T mispairs and is thought to initiate base excision repair (BER) of deaminated 5-methylcytosine (mC). Recent studies show that TDG, including its glycosylase activity, is essential for active DNA demethylation and embryonic development. These and other findings suggest that active demethylation could involve mC deamination by a deaminase, giving a G·T mispair followed by TDG-initiated BER. An alternative proposal is that demethylation could involve iterative oxidation of mC to 5-hydroxymethylcytosine (hmC) and then to 5-formylcytosine (fC) and 5-carboxylcytosine (caC), mediated by a Tet (ten eleven translocation) enzyme, with conversion of caC to C by a putative decarboxylase. Our previous studies suggest that TDG could excise fC and caC from DNA, which could provide another potential demethylation mechanism. We show here that TDG rapidly removes fC, with higher activity than for G·T mispairs, and has substantial caC excision activity, yet it cannot remove hmC. TDG excision of fC and caC, oxidation products of mC, is consistent with its strong specificity for excising bases from a CpG context. Our findings reveal a remarkable new aspect of specificity for TDG, inform its catalytic mechanism, and suggest that TDG could protect against fC-induced mutagenesis. The results also suggest a new potential mechanism for active DNA demethylation, involving TDG excision of Tet-produced fC (or caC) and subsequent BER. Such a mechanism obviates the need for a decarboxylase and is consistent with findings that TDG glycosylase activity is essential for active demethylation and embryonic development, as are mechanisms involving TDG excision of deaminated mC or hmC.
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Affiliation(s)
- Atanu Maiti
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
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Simmons JM, Koslowsky DJ, Hausinger RP. Trypanosoma brucei brucei: thymine 7-hydroxylase-like proteins. Exp Parasitol 2009; 124:453-8. [PMID: 19945457 DOI: 10.1016/j.exppara.2009.11.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 11/17/2009] [Accepted: 11/23/2009] [Indexed: 01/29/2023]
Abstract
Two genes from Trypanosoma brucei brucei are predicted to encode Fe(II)- and alpha-ketoglutarate-dependent enzymes related to fungal thymine 7-hydroxylase. Transcription of the thymine hydroxylase-like genes is up-regulated in the bloodstream form of the parasite over the insect form, whereas Western blot analysis indicates more cross-reactive protein in the latter life stage. The genes were cloned, the proteins purified from Escherichia coli, and both proteins were shown to bind Fe(II) and alpha-ketoglutarate, confirming proper folding. The isolated proteins were incubated with Fe(II)- and alpha-ketoglutarate plus thymine, thymidine, and other putative substrates, but no activity was detected. Furthermore, no thymine 7-hydroxylase activity was detected in extracts of procyclic or bloodstream form cells. Although the functions of these proteins remain unknown, we conclude they are unlikely to be involved in thymine salvage.
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Affiliation(s)
- Jana M Simmons
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, United States
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