1
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Dubini RCA, Korytiaková E, Schinkel T, Heinrichs P, Carell T, Rovó P. 1H NMR Chemical Exchange Techniques Reveal Local and Global Effects of Oxidized Cytosine Derivatives. ACS PHYSICAL CHEMISTRY AU 2022; 2:237-246. [PMID: 35637781 PMCID: PMC9137243 DOI: 10.1021/acsphyschemau.1c00050] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 01/25/2022] [Accepted: 01/26/2022] [Indexed: 11/29/2022]
Abstract
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5-Carboxycytosine
(5caC) is a rare epigenetic modification found
in nucleic acids of all domains of life. Despite its sparse genomic
abundance, 5caC is presumed to play essential regulatory roles in
transcription, maintenance and base-excision processes in DNA. In
this work, we utilize nuclear magnetic resonance (NMR) spectroscopy
to address the effects of 5caC incorporation into canonical DNA strands
at multiple pH and temperature conditions. Our results demonstrate
that 5caC has a pH-dependent global destabilizing and a base-pair
mobility enhancing local impact on dsDNA, albeit without any detectable
influence on the ground-state B-DNA structure. Measurement of hybridization
thermodynamics and kinetics of 5caC-bearing DNA duplexes highlighted
how acidic environment (pH 5.8 and 4.7) destabilizes the double-stranded
structure by ∼10–20 kJ mol–1 at 37
°C when compared to the same sample at neutral pH. Protonation
of 5caC results in a lower activation energy for the dissociation
process and a higher barrier for annealing. Studies on conformational
exchange on the microsecond time scale regime revealed a sharply localized
base-pair motion involving exclusively the modified site and its immediate
surroundings. By direct comparison with canonical and 5-formylcytosine
(5fC)-edited strands, we were able to address the impact of the two
most oxidized naturally occurring cytosine derivatives in the genome.
These insights on 5caC’s subtle sensitivity to acidic pH contribute
to the long-standing questions of its capacity as a substrate in base
excision repair processes and its purpose as an independent, stable
epigenetic mark.
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Affiliation(s)
- Romeo C. A. Dubini
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
- Center for Nanoscience (CeNS), Faculty of Physics, Ludwig-Maximilians-Universität München, Schellingstraße 4, 5th floor, 80799 Munich, Germany
| | - Eva Korytiaková
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
| | - Thea Schinkel
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
| | - Pia Heinrichs
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
| | - Thomas Carell
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
| | - Petra Rovó
- Faculty of Chemistry and Pharmacy, Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstraße 5-13, 81377 Munich, Germany
- Center for Nanoscience (CeNS), Faculty of Physics, Ludwig-Maximilians-Universität München, Schellingstraße 4, 5th floor, 80799 Munich, Germany
- Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
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2
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Vongsutilers V, Shinohara Y, Kawai G. Epigenetic TET-Catalyzed Oxidative Products of 5-Methylcytosine Impede Z-DNA Formation of CG Decamers. ACS OMEGA 2020; 5:8056-8064. [PMID: 32309715 PMCID: PMC7161056 DOI: 10.1021/acsomega.0c00120] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Accepted: 03/19/2020] [Indexed: 05/12/2023]
Abstract
Methylation of cytosine has been known to play a significant role in epigenetic regulation. 5-Methylcytosine was among the first base modification that was discovered for the capability to facilitate B/Z-DNA transition as observed in CG repeated tracks. A study on gene repression by Z-DNA prone sequence as in ADAM-12 has ignited our research interest for the Z-DNA role in epigenetics. Ten eleven translocation family proteins are responsible to catalyze 5-methylcytosine to produce oxidative products including 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxycytosine, which each may have unique function rather than the sole purpose of 5-methylcytosine clearance. Although the Z-DNA-promoting effect of 5-methylcytosine was well established, the effect of its oxidative products on Z-DNA remain unknown. In this study, the Z-DNA-promoting effect of 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxycytosine on the CG decamer model were investigated along with known Z-DNA stabilizers, 5-methylcytosine and 8-oxoguanine. Experimental results from circular dichroism (CD) and NMR indicates that all oxidative products of 5-methylcytosine hinder B/Z-DNA transition as high salt concentration suitable to stabilize and convert unmodified CG decamer to Z-DNA conformation is insufficient to facilitate the B/Z-DNA transition of CG decamer containing 5-hydroxymethylcytosine, 5-formylcytosine, or 5-carboxycytosine. Molecular dynamic simulation and free energy calculation by MM-PBSA are in agreement with the experimental finding that 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxycytosine destabilize Z-DNA conformation of CG decamer, in contrast to its precursor. Investigation of Z-DNA switch-on/switch-off regulated by 5-methylcytosine and its oxidative products is a further step to elucidate the potential of epigenetic regulated via Z-DNA.
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Affiliation(s)
- Vorasit Vongsutilers
- Department
of Food and Pharmaceutical Chemistry, Chulalongkorn
University, Bangkok 10330, Thailand
| | - Yoko Shinohara
- Department
of Life and Environmental Sciences, Chiba
Institute of Technology, Chiba 275-0016, Japan
| | - Gota Kawai
- Department
of Life and Environmental Sciences, Chiba
Institute of Technology, Chiba 275-0016, Japan
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3
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Sanstead PJ, Ashwood B, Dai Q, He C, Tokmakoff A. Oxidized Derivatives of 5-Methylcytosine Alter the Stability and Dehybridization Dynamics of Duplex DNA. J Phys Chem B 2020; 124:1160-1174. [PMID: 31986043 PMCID: PMC7136776 DOI: 10.1021/acs.jpcb.9b11511] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The naturally occurring nucleobase 5-methylcytosine (mC) and its oxidized derivatives 5-hydroxymethylcytosine (hmC), 5-formylcytosine (fC), and 5-carboxylcytosine (caC) play important roles in epigenetic regulation and, along with cytosine (C), represent nucleobases currently implicated in the active cytosine demethylation pathway. Despite considerable interest in these modified bases, their impact on the thermodynamic stability of double-stranded DNA (dsDNA) remains ambiguous and their influence on hybridization kinetics and dynamics is even less well-understood. To address these unknowns, we employ steady-state and time-resolved infrared spectroscopy to measure the influence of cytosine modification on the thermodynamics and kinetics of hybridization by assessing the impact on local base pairing dynamics, shifts in the stability of the duplex state, and changes to the hybridization transition state. Modification with mC leads to more tightly bound base pairing below the melting transition and stabilizes the duplex relative to canonical DNA, but the free energy barrier to dehybridization at physiological temperature is nevertheless reduced slightly. Both hmC and fC lead to an increase in local base pair fluctuations, a reduction in the cooperativity of duplex melting, and a lowering of the dissociation barrier, but these effects are most pronounced when the 5-position is formylated. The caC nucleobase demonstrates little impact on dsDNA under neutral conditions, but we find that this modification can dynamically switch between C-like and fC-like behavior depending on the protonation state of the 5-position carboxyl group. Our results provide a consistent thermodynamic and kinetic framework with which to describe the modulation of the physical properties of double-stranded DNA containing these modified nucleobases.
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Affiliation(s)
- Paul J. Sanstead
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Brennan Ashwood
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Qing Dai
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Chuan He
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
- Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Andrei Tokmakoff
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
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4
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Ashwood B, Sanstead PJ, Dai Q, He C, Tokmakoff A. 5-Carboxylcytosine and Cytosine Protonation Distinctly Alter the Stability and Dehybridization Dynamics of the DNA Duplex. J Phys Chem B 2020; 124:627-640. [PMID: 31873021 DOI: 10.1021/acs.jpcb.9b11510] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Applications associated with nucleobase protonation events are grounded in their fundamental impact on DNA thermodynamics, structure, and hybridization dynamics. Of the canonical nucleobases, N3 protonation of cytosine (C) is the most widely utilized in both biology and nanotechnology. Naturally occurring C derivatives that shift the N3 pKa introduce an additional level of tunability. The epigenetic nucleobase 5-carboxylcytosine (caC) presents a particularly interesting example since this derivative forms Watson-Crick base pairs of similar stability and displays pH-dependent behavior over the same range as the canonical nucleobase. However, the titratable group in caC corresponds to the exocyclic carboxyl group rather than N3, and the implications of these divergent protonation events toward DNA hybridization thermodynamics, kinetics, and base pairing dynamics remain poorly understood. Here, we study the pH dependence of these physical properties using model oligonucleotides containing C and caC with FTIR and temperature-jump IR spectroscopy. We demonstrate that N3 protonation of C completely disrupts duplex stability, leading to large shifts in the duplex/single-strand equilibrium, a reduction in the cooperativity of melting, and an acceleration in the rate of duplex dissociation. In contrast, while increasing 5-carboxyl protonation in caC-containing duplexes induces an increase in base pair fluctuations, the DNA duplex can tolerate substantial protonation without significant perturbation to the duplex/single-strand equilibrium. However, 5-carboxyl protonation has a large impact on hybridization kinetics by reducing the transition state free energy. Our thermodynamic and kinetic analysis provides new insight on the impact of two divergent protonation mechanisms in naturally occurring nucleobases on the biophysical properties of DNA.
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5
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Pidugu LS, Dai Q, Malik SS, Pozharski E, Drohat AC. Excision of 5-Carboxylcytosine by Thymine DNA Glycosylase. J Am Chem Soc 2019; 141:18851-18861. [PMID: 31693361 DOI: 10.1021/jacs.9b10376] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
5-Methylcytosine (mC) is an epigenetic mark that is written by methyltransferases, erased through passive and active mechanisms, and impacts transcription, development, diseases including cancer, and aging. Active DNA demethylation involves TET-mediated stepwise oxidation of mC to 5-hydroxymethylcytosine, 5-formylcytosine (fC), or 5-carboxylcytosine (caC), excision of fC or caC by thymine DNA glycosylase (TDG), and subsequent base excision repair. Many elements of this essential process are poorly defined, including TDG excision of caC. To address this problem, we solved high-resolution structures of human TDG bound to DNA with cadC (5-carboxyl-2'-deoxycytidine) flipped into its active site. The structures unveil detailed enzyme-substrate interactions that mediate recognition and removal of caC, many involving water molecules. Importantly, two water molecules contact a carboxylate oxygen of caC and are poised to facilitate acid-catalyzed caC excision. Moreover, a substrate-dependent conformational change in TDG modulates the hydrogen bond interactions for one of these waters, enabling productive interaction with caC. An Asn residue (N191) that is critical for caC excision is found to contact N3 and N4 of caC, suggesting a mechanism for acid-catalyzed base excision that features an N3-protonated form of caC but would be ineffective for C, mC, or hmC. We also investigated another Asn residue (N140) that is catalytically essential and strictly conserved in the TDG-MUG enzyme family. A structure of N140A-TDG bound to cadC DNA provides the first high-resolution insight into how enzyme-substrate interactions, including water molecules, are impacted by depleting the conserved Asn, informing its role in binding and addition of the nucleophilic water molecule.
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Affiliation(s)
- Lakshmi S Pidugu
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Qing Dai
- Department of Chemistry , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Shuja S Malik
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Edwin Pozharski
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States.,Center for Biomolecular Therapeutics , Institute for Bioscience and Biotechnology Research , Rockville , Maryland 20850 , United States
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
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6
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Hardwick JS, Lane AN, Brown T. Epigenetic Modifications of Cytosine: Biophysical Properties, Regulation, and Function in Mammalian DNA. Bioessays 2018; 40. [DOI: 10.1002/bies.201700199] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 12/13/2017] [Indexed: 12/21/2022]
Affiliation(s)
- Jack S. Hardwick
- Chemistry Research Laboratory; Department of Chemistry; University of Oxford; 12 Mansfield Road Oxford OX1 3TA UK
| | - Andrew N. Lane
- Department of Toxicology and Cancer Biology; University of Kentucky; 789 S. Limestone St. Lexington KY 40536 USA
| | - Tom Brown
- Chemistry Research Laboratory; Department of Chemistry; University of Oxford; 12 Mansfield Road Oxford OX1 3TA UK
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7
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Muñoz-López Á, Summerer D. Recognition of Oxidized 5-Methylcytosine Derivatives in DNA by Natural and Engineered Protein Scaffolds. CHEM REC 2017; 18:105-116. [PMID: 29251421 DOI: 10.1002/tcr.201700088] [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: 10/06/2017] [Indexed: 12/14/2022]
Abstract
Methylation of genomic cytosine to 5-methylcytosine is a central regulatory element of mammalian gene expression with important roles in development and disease. 5-methylcytosine can be actively reversed to cytosine via oxidation to 5-hydroxymethyl-, 5-formyl-, and 5-carboxylcytosine by ten-eleven-translocation dioxygenases and subsequent base excision repair or replication-dependent dilution. Moreover, the oxidized 5-methylcytosine derivatives are potential epigenetic marks with unique biological roles. Key to a better understanding of these roles are insights into the interactions of the nucleobases with DNA-binding protein scaffolds: Natural scaffolds involved in transcription, 5-methylcytosine-reading and -editing as well as general chromatin organization can be selectively recruited or repulsed by oxidized 5-methylcytosines, forming the basis of their biological functions. Moreover, designer protein scaffolds engineered for the selective recognition of oxidized 5-methylcytosines are valuable tools to analyze their genomic levels and distribution. Here, we review recent structural and functional insights into the molecular recognition of oxidized 5-methylcytosine derivatives in DNA by selected protein scaffolds.
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Affiliation(s)
- Álvaro Muñoz-López
- Faculty of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund
| | - Daniel Summerer
- Faculty of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund
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8
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Michaelides IN, Tago N, Viverge B, Carell T. Synthesis of RNA Containing 5-Hydroxymethyl-, 5-Formyl-, and 5-Carboxycytidine. Chemistry 2017; 23:15894-15898. [PMID: 28906048 DOI: 10.1002/chem.201704216] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Indexed: 12/17/2022]
Abstract
5-Hydroxymethyl-, 5-formyl-, and 5-carboxy-2'-deoxycytidine are new epigenetic bases (hmdC, fdC, cadC) that were recently discovered in the DNA of higher eukaryotes. The same bases (5-hydroxymethyl-, 5-formyl-, and 5-carboxycytidine; hmC, fC, and caC) have now also been detected in mammalian RNA with a high abundance in mRNA. While DNA phosphoramidites (PAs) that allow the synthesis of xdC-containing oligonucleotides for deeper biological studies are available, the corresponding silyl-protected RNA PAs for fC and caC have not yet been disclosed. Here, we report novel RNA PAs for hmC, fC, and caC that can be used in routine RNA synthesis. The new building blocks are compatible with the canonical PAs and also with themselves, which enables even the synthesis of RNA strands containing all three of these bases. The study will pave the way for detailed physical, biochemical, and biological studies to unravel the function of these non-canonical modifications in RNA.
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Affiliation(s)
- Iacovos N Michaelides
- Center for Integrated Protein Science at the Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, Munich, Germany.,Current address: AstraZeneca, 310 Cambridge Science Park, Milton Road, Cambridge, CB4 0FZ, UK
| | - Nobuhiro Tago
- Center for Integrated Protein Science at the Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, Munich, Germany
| | - Bastien Viverge
- Center for Integrated Protein Science at the Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, Munich, Germany
| | - Thomas Carell
- Center for Integrated Protein Science at the Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, Munich, Germany
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9
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Hong T, Wu F, Fu B, Yuan Y, Xu J, Wang T, Zhou X. 5-Formylcytosine and 5-Carboxylcytosine Significantly Reduce the Catalytic Activity of Hhal DNA Methyltransferase. CHINESE J CHEM 2017. [DOI: 10.1002/cjoc.201600879] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Tingting Hong
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Fan Wu
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Boshi Fu
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Yushu Yuan
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Jinglei Xu
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Tianlu Wang
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
| | - Xiang Zhou
- College of Chemistry and Molecular Sciences, The Institute for Advanced Studies; Wuhan University; Wuhan Hubei 430072 China
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10
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Jin L, Lv M, Wei Y, Lu J, Min S. Reactivity of 5-carboxycytosine toward addition and hydrogen abstraction by ·OH in acetonitrile: a computational study. MOLECULAR SIMULATION 2017. [DOI: 10.1080/08927022.2017.1279286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Lingxia Jin
- Shaanxi Key Laboratory of Catalysis, School of Chemical & Environment Science, Shaanxi Sci-Tech University, Hanzhong, P.R. China
| | - Mengdan Lv
- Shaanxi Key Laboratory of Catalysis, School of Chemical & Environment Science, Shaanxi Sci-Tech University, Hanzhong, P.R. China
| | - Yawen Wei
- Periodical Offices of Chang’an University, Chang’an University, Xi’an, P.R. China
| | - Jiufu Lu
- Shaanxi Key Laboratory of Catalysis, School of Chemical & Environment Science, Shaanxi Sci-Tech University, Hanzhong, P.R. China
| | - Suotian Min
- Shaanxi Key Laboratory of Catalysis, School of Chemical & Environment Science, Shaanxi Sci-Tech University, Hanzhong, P.R. China
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11
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Drohat AC, Coey CT. Role of Base Excision "Repair" Enzymes in Erasing Epigenetic Marks from DNA. Chem Rev 2016; 116:12711-12729. [PMID: 27501078 DOI: 10.1021/acs.chemrev.6b00191] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Base excision repair (BER) is one of several DNA repair pathways found in all three domains of life. BER counters the mutagenic and cytotoxic effects of damage that occurs continuously to the nitrogenous bases in DNA, and its critical role in maintaining genomic integrity is well established. However, BER also performs essential functions in processes other than DNA repair, where it acts on naturally modified bases in DNA. A prominent example is the central role of BER in mediating active DNA demethylation, a multistep process that erases the epigenetic mark 5-methylcytosine (5mC), and derivatives thereof, converting them back to cytosine. Herein, we review recent advances in the understanding of how BER mediates this critical component of epigenetic regulation in plants and animals.
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Affiliation(s)
- Alexander C Drohat
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine , Baltimore, Maryland 21201, United States
| | - Christopher T Coey
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine , Baltimore, Maryland 21201, United States
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12
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Rathi P, Maurer S, Kubik G, Summerer D. Isolation of Human Genomic DNA Sequences with Expanded Nucleobase Selectivity. J Am Chem Soc 2016; 138:9910-8. [PMID: 27429302 DOI: 10.1021/jacs.6b04807] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the direct isolation of user-defined DNA sequences from the human genome with programmable selectivity for both canonical and epigenetic nucleobases. This is enabled by the use of engineered transcription-activator-like effectors (TALEs) as DNA major groove-binding probes in affinity enrichment. The approach provides the direct quantification of 5-methylcytosine (5mC) levels at single genomic nucleotide positions in a strand-specific manner. We demonstrate the simple, multiplexed typing of a variety of epigenetic cancer biomarker 5mC with custom TALE mixes. Compared to antibodies as the most widely used affinity probes for 5mC analysis, i.e., employed in the methylated DNA immunoprecipitation (MeDIP) protocol, TALEs provide superior sensitivity, resolution and technical ease. We engineer a range of size-reduced TALE repeats and establish full selectivity profiles for their binding to all five human cytosine nucleobases. These provide insights into their nucleobase recognition mechanisms and reveal the ability of TALEs to isolate genomic target sequences with selectivity for single 5-hydroxymethylcytosine and, in combination with sodium borohydride reduction, single 5-formylcytosine nucleobases.
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Affiliation(s)
- Preeti Rathi
- Department of Chemistry and Chemical Biology, Technical University of Dortmund , Otto-Hahn-Str. 6, 44227 Dortmund, Germany
| | - Sara Maurer
- Department of Chemistry and Chemical Biology, Technical University of Dortmund , Otto-Hahn-Str. 6, 44227 Dortmund, Germany
| | - Grzegorz Kubik
- Department of Chemistry and Chemical Biology, Technical University of Dortmund , Otto-Hahn-Str. 6, 44227 Dortmund, Germany
| | - Daniel Summerer
- Department of Chemistry and Chemical Biology, Technical University of Dortmund , Otto-Hahn-Str. 6, 44227 Dortmund, Germany
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13
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Dai Q, Sanstead PJ, Peng CS, Han D, He C, Tokmakoff A. Weakened N3 Hydrogen Bonding by 5-Formylcytosine and 5-Carboxylcytosine Reduces Their Base-Pairing Stability. ACS Chem Biol 2016; 11:470-7. [PMID: 26641274 DOI: 10.1021/acschembio.5b00762] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In the active cytosine demethylation pathway, 5-methylcytosine (5mC) is oxidized sequentially to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Thymine DNA glycosylase (TDG) selectively excises 5fC and 5caC but not cytosine (C), 5mC, and 5hmC. We propose that the electron-withdrawing properties of -CHO and -COOH in 5fC and 5caC increase N3 acidity, leading to weakened hydrogen bonding and reduced base pair stability relative to C, 5mC, and 5hmC, thereby facilitating the selective recognition of 5fC and 5caC by TDG. Through (13)C NMR, we measured the pKa at N3 of 5fC as 2.4 and the two pKa's of 5caC as 2.1 and 4.2. We used isotope-edited IR spectroscopy coupled with density functional theory (DFT) calculations to site-specifically assign the more acidic pKa of 5caC to protonation at N3, indicating that N3 acidity is increased in 5fC and 5caC relative to C. IR and UV melting studies of self-complementary DNA oligomers confirm reduced stability for 5fC-G and 5caC-G base pairs. Furthermore, while the 5fC-G base pair stability is insensitive to pH, the 5caC-G stability is reduced as pH decreases and the carboxyl group is increasingly protonated. Despite suggestions that 5fC and 5caC may exist in rare tautomeric structures which form wobble GC base pairs, our two-dimensional infrared (2D IR) spectroscopy of 5fC and 5caC free nucleosides confirms that both bases are predominantly in the canonical amino-keto form. Taken together, these findings support our model that weakened base pairing ability for 5fC and 5caC in dsDNA contributes to their selective recognition by TDG.
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Affiliation(s)
- Qing Dai
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Paul J. Sanstead
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Chunte Sam Peng
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Dali Han
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Chuan He
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Andrei Tokmakoff
- Department of Chemistry, ‡Institute for Biophysical
Dynamics, §James Franck Institute, ∥Department of Biochemistry
and Molecular Biology, and ⊥Howard Hughes Medical Institute, The University of Chicago, Chicago, Illinois 60637, United States
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14
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Kubik G, Summerer D. Deciphering Epigenetic Cytosine Modifications by Direct Molecular Recognition. ACS Chem Biol 2015; 10:1580-9. [PMID: 25897631 DOI: 10.1021/acschembio.5b00158] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Epigenetic modification at the 5-position of cytosine is a key regulatory element of mammalian gene expression with important roles in genome stability, development, and disease. The repertoire of cytosine modifications has long been confined to only 5-methylcytosine (mC) but has recently been expanded by the discovery of 5-hydroxymethyl-, 5-formyl-, and 5-carboxylcytosine. These are key intermediates of active mC demethylation but may additionally represent new epigenetic marks with distinct biological roles. This leap in chemical complexity of epigenetic cytosine modifications has not only created a pressing need for analytical approaches that enable unraveling of their functions, it has also created new challenges for such analyses with respect to sensitivity and selectivity. The crucial step of any such approach that defines its analytic potential is the strategy used for the actual differentiation of the cytosine 5-modifications from one another, and this selectivity can in principle be provided either by chemoselective conversions or by selective, molecular recognition events. While the former strategy has been particularly successful for accurate genomic profiling of cytosine modifications in vitro, the latter strategy provides interesting perspectives for simplified profiling of natural, untreated DNA, as well as for emerging applications such as single cell analysis and the monitoring of cytosine modification in vivo. We here review analytical techniques for the deciphering of epigenetic cytosine modifications with an emphasis on approaches that are based on the direct molecular recognition of these modifications in DNA.
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Affiliation(s)
- Grzegorz Kubik
- Department of Chemistry,
Zukunftskolleg, and Konstanz Research School Chemical Biology, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
| | - Daniel Summerer
- Department of Chemistry,
Zukunftskolleg, and Konstanz Research School Chemical Biology, University of Konstanz, Universitätsstraße 10, 78457 Konstanz, Germany
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15
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Du C, Kurabe N, Matsushima Y, Suzuki M, Kahyo T, Ohnishi I, Tanioka F, Tajima S, Goto M, Yamada H, Tao H, Shinmura K, Konno H, Sugimura H. Robust quantitative assessments of cytosine modifications and changes in the expressions of related enzymes in gastric cancer. Gastric Cancer 2015; 18:516-25. [PMID: 25098926 DOI: 10.1007/s10120-014-0409-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Accepted: 07/13/2014] [Indexed: 02/07/2023]
Abstract
BACKGROUND The rediscovery of 5-hydroxymethylcytosine, the ten-eleven translocation (TET) family, thymine-DNA glycosylase (TDG) and isocitrate dehydrogenase (IDH) have opened new avenues in the study of DNA demethylation pathways in gastric cancer (GC). We performed a comprehensive and robust analysis of these genes and modified cytosines in gastric cancer. METHODS Liquid chromatography mass spectrometry/mass spectrometry (LC-MS/MS) was used to assess 5-methyldeoxycytidine (5-mC), 5-hydroxymethyldeoxycytidine (5-hmC), 5-formyldeoxycytidine (5-fC) and 5-carboxyldeoxycytidine (5-caC) quantitatively in tumorous and non-tumorous regions of GCs; [D2]-5-hmC was used as an internal standard. Expression levels of the genes TET1, TET2, TET3, TDG, IDH1 and IDH2 were measured using a real-time reverse transcription polymerase chain reaction (RT-PCR) and were compared to the clinical attributes of each case. Using HEK293T cells the effects of introducing plasmids containing full-length TET1, TET2, and TET3 and 7 variants of the TET2 catalytic domain were evaluated in terms of their effect on cytosine demethylation. RESULTS LC-MS/MS showed that 5-hmC was significantly decreased in tumorous portions. 5-mC was also moderately decreased in tumors, while 5-fC and 5-caC were barely detectable. The expressions of TET1, TET2, TET3, TDG and IDH2, but not IDH1, were notably decreased in GCs, compared with the adjacent non-tumor portion. TET1 expression and the 5-hmC levels determined using LC-MS/MS had a significantly positive correlation and TET1 protein had a greater effect on the increase in 5-hmC than TET2 and TET3 in HEK293T cells. CONCLUSIONS The loss of 5-hmC and the down-regulation of TET1-3, TDG and IDH2 were found in GCs. The loss of 5-hmC in GCs was mainly correlated with the down-regulation of TET1.
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Affiliation(s)
- Chunping Du
- Department of Tumor Pathology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi Ward, Hamamatsu, Shizuoka, 431-3192, Japan
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16
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Drohat AC, Maiti A. Mechanisms for enzymatic cleavage of the N-glycosidic bond in DNA. Org Biomol Chem 2015; 12:8367-78. [PMID: 25181003 DOI: 10.1039/c4ob01063a] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
DNA glycosylases remove damaged or enzymatically modified nucleobases from DNA, thereby initiating the base excision repair (BER) pathway, which is found in all forms of life. These ubiquitous enzymes promote genomic integrity by initiating repair of mutagenic and/or cytotoxic lesions that arise continuously due to alkylation, deamination, or oxidation of the normal bases in DNA. Glycosylases also perform essential roles in epigenetic regulation of gene expression, by targeting enzymatically-modified forms of the canonical DNA bases. Monofunctional DNA glycosylases hydrolyze the N-glycosidic bond to liberate the target base, while bifunctional glycosylases mediate glycosyl transfer using an amine group of the enzyme, generating a Schiff base intermediate that facilitates their second activity, cleavage of the DNA backbone. Here we review recent advances in understanding the chemical mechanism of monofunctional DNA glycosylases, with an emphasis on how the reactions are influenced by the properties of the nucleobase leaving-group, the moiety that varies across the vast range of substrates targeted by these enzymes.
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Affiliation(s)
- Alexander C Drohat
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA.
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17
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Szulik M, Pallan PS, Nocek B, Voehler M, Banerjee S, Brooks S, Joachimiak A, Egli M, Eichman BF, Stone MP. Differential stabilities and sequence-dependent base pair opening dynamics of Watson-Crick base pairs with 5-hydroxymethylcytosine, 5-formylcytosine, or 5-carboxylcytosine. Biochemistry 2015; 54:1294-305. [PMID: 25632825 PMCID: PMC4325598 DOI: 10.1021/bi501534x] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
5-Hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) form during active demethylation of 5-methylcytosine (5mC) and are implicated in epigenetic regulation of the genome. They are differentially processed by thymine DNA glycosylase (TDG), an enzyme involved in active demethylation of 5mC. Three modified Dickerson-Drew dodecamer (DDD) sequences, amenable to crystallographic and spectroscopic analyses and containing the 5'-CG-3' sequence associated with genomic cytosine methylation, containing 5hmC, 5fC, or 5caC placed site-specifically into the 5'-T(8)X(9)G(10)-3' sequence of the DDD, were compared. The presence of 5caC at the X(9) base increased the stability of the DDD, whereas 5hmC or 5fC did not. Both 5hmC and 5fC increased imino proton exchange rates and calculated rate constants for base pair opening at the neighboring base pair A(5):T(8), whereas 5caC did not. At the oxidized base pair G(4):X(9), 5fC exhibited an increase in the imino proton exchange rate and the calculated kop. In all cases, minimal effects to imino proton exchange rates occurred at the neighboring base pair C(3):G(10). No evidence was observed for imino tautomerization, accompanied by wobble base pairing, for 5hmC, 5fC, or 5caC when positioned at base pair G(4):X(9); each favored Watson-Crick base pairing. However, both 5fC and 5caC exhibited intranucleobase hydrogen bonding between their formyl or carboxyl oxygens, respectively, and the adjacent cytosine N(4) exocyclic amines. The lesion-specific differences observed in the DDD may be implicated in recognition of 5hmC, 5fC, or 5caC in DNA by TDG. However, they do not correlate with differential excision of 5hmC, 5fC, or 5caC by TDG, which may be mediated by differences in transition states of the enzyme-bound complexes.
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Affiliation(s)
- Marta
W. Szulik
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Pradeep S. Pallan
- Department
of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, School of
Medicine, Vanderbilt University, Nashville, Tennessee 37232, United States
| | - Boguslaw Nocek
- Bioscience
Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Markus Voehler
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Surajit Banerjee
- Northeastern
Collaborative Access Team and Department of Chemistry and Chemical
Biology, Cornell University, Argonne National
Laboratory, Argonne, Illinois 60439, United
States
| | - Sonja Brooks
- Department
of Biological Sciences, Vanderbilt Institute of Chemical Biology,
and Center for Structural Biology, Vanderbilt
University, Nashville, Tennessee 37235, United States
| | - Andrzej Joachimiak
- Bioscience
Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Martin Egli
- Department
of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, School of
Medicine, Vanderbilt University, Nashville, Tennessee 37232, United States
| | - Brandt F. Eichman
- Department
of Biological Sciences, Vanderbilt Institute of Chemical Biology,
and Center for Structural Biology, Vanderbilt
University, Nashville, Tennessee 37235, United States
| | - Michael P. Stone
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States,(M.P.S.) Tel.: 615-322-2589; E-mail:
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18
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Jin L, Zhao C, Zhang T, Wang Z, Min S, Wang W, Wei Y. Effects of an acid–alkaline environment on the reactivity of 5-carboxycytosine with hydroxyl radicals. RSC Adv 2015. [DOI: 10.1039/c5ra17393k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The addition of ˙OH to C5C6 double bond and abstraction of H5 from 5-caCyt are more favourable in neutral, acidic and alkaline conditions.
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Affiliation(s)
- Lingxia Jin
- Shaanxi Province Key Laboratory of Catalytic Fundamentals & Applications
- School of Chemical & Environment Science
- Shaanxi University of Technology
- Hanzhong
- China
| | - Caibin Zhao
- Shaanxi Province Key Laboratory of Catalytic Fundamentals & Applications
- School of Chemical & Environment Science
- Shaanxi University of Technology
- Hanzhong
- China
| | - Tianlei Zhang
- Shaanxi Province Key Laboratory of Catalytic Fundamentals & Applications
- School of Chemical & Environment Science
- Shaanxi University of Technology
- Hanzhong
- China
| | - Zhiyin Wang
- Shaanxi Province Key Laboratory of Catalytic Fundamentals & Applications
- School of Chemical & Environment Science
- Shaanxi University of Technology
- Hanzhong
- China
| | - Suotian Min
- Shaanxi Province Key Laboratory of Catalytic Fundamentals & Applications
- School of Chemical & Environment Science
- Shaanxi University of Technology
- Hanzhong
- China
| | - Wenliang Wang
- Key Laboratory for Macromolecular Science of Shaanxi Province
- School of Chemistry and Chemical Engineering
- Shaanxi Normal University
- Xi’an 710062
- China
| | - Yawen Wei
- Institute of Publication Science
- Chang’an University
- Xi’an 710064
- China
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19
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Maiti A, Michelson AZ, Armwood CJ, Lee JK, Drohat AC. Divergent mechanisms for enzymatic excision of 5-formylcytosine and 5-carboxylcytosine from DNA. J Am Chem Soc 2013; 135:15813-22. [PMID: 24063363 DOI: 10.1021/ja406444x] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
5-Methylcytosine (mC) is an epigenetic mark that impacts transcription, development, and genome stability, and aberrant DNA methylation contributes to aging and cancer. Active DNA demethylation involves stepwise oxidation of mC to 5-hydroxymethylcytosine, 5-formylcytosine (fC), and potentially 5-carboxylcytosine (caC), excision of fC or caC by thymine DNA glycosylase (TDG), and restoration of cytosine via follow-on base excision repair. Here, we investigate the mechanism for TDG excision of fC and caC. We find that 5-carboxyl-2'-deoxycytidine ionizes with pK(a) values of 4.28 (N3) and 2.45 (carboxyl), confirming that caC exists as a monoanion at physiological pH. Calculations do not support the proposal that G·fC and G·caC base pairs adopt a wobble structure that is recognized by TDG. Previous studies show that N-glycosidic bond hydrolysis follows a stepwise (S(N)1) mechanism, and that TDG activity increases with pyrimidine N1 acidity, that is, leaving group quality of the target base. Calculations here show that fC and the neutral tautomers of caC are acidic relative to other TDG substrates, but the caC monoanion exhibits poor acidity and likely resists TDG excision. While fC activity is independent of pH, caC excision is acid-catalyzed, and the pH profile indicates that caC ionizes in the enzyme-substrate complex with an apparent pKa of 5.8, likely at N3. Mutational analysis reveals that Asn191 is essential for excision of caC but dispensable for fC activity, indicating that N191 may stabilize N3-protonated forms of caC to facilitate acid catalysis and suggesting that N191A-TDG could potentially be useful for studying DNA demethylation in cells.
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Affiliation(s)
- Atanu Maiti
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine , Baltimore, Maryland 21201, United States
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20
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First X-ray diffraction and quantum chemical study of proton-acceptor and proton-donor forms of 5-carboxylcytosine, the last-discovered nucleobase. J Mol Struct 2013. [DOI: 10.1016/j.molstruc.2013.07.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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21
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Hashimoto H, Hong S, Bhagwat AS, Zhang X, Cheng X. Excision of 5-hydroxymethyluracil and 5-carboxylcytosine by the thymine DNA glycosylase domain: its structural basis and implications for active DNA demethylation. Nucleic Acids Res 2012; 40:10203-14. [PMID: 22962365 PMCID: PMC3488261 DOI: 10.1093/nar/gks845] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The mammalian thymine DNA glycosylase (TDG) is implicated in active DNA demethylation via the base excision repair pathway. TDG excises the mismatched base from G:X mismatches, where X is uracil, thymine or 5-hydroxymethyluracil (5hmU). These are, respectively, the deamination products of cytosine, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC). In addition, TDG excises the Tet protein products 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) but not 5hmC and 5mC, when paired with a guanine. Here we present a post-reactive complex structure of the human TDG domain with a 28-base pair DNA containing a G:5hmU mismatch. TDG flips the target nucleotide from the double-stranded DNA, cleaves the N-glycosidic bond and leaves the C1' hydrolyzed abasic sugar in the flipped state. The cleaved 5hmU base remains in a binding pocket of the enzyme. TDG allows hydrogen-bonding interactions to both T/U-based (5hmU) and C-based (5caC) modifications, thus enabling its activity on a wider range of substrates. We further show that the TDG catalytic domain has higher activity for 5caC at a lower pH (5.5) as compared to the activities at higher pH (7.5 and 8.0) and that the structurally related Escherichia coli mismatch uracil glycosylase can excise 5caC as well. We discuss several possible mechanisms, including the amino-imino tautomerization of the substrate base that may explain how TDG discriminates against 5hmC and 5mC.
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Affiliation(s)
- Hideharu Hashimoto
- Department of Biochemistry, Emory University School of Medicine, 1510 Clifton Road, Atlanta, GA 30322, USA
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22
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Münzel M, Lischke U, Stathis D, Pfaffeneder T, Gnerlich FA, Deiml CA, Koch SC, Karaghiosoff K, Carell T. Improved synthesis and mutagenicity of oligonucleotides containing 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine. Chemistry 2011; 17:13782-8. [PMID: 22069110 DOI: 10.1002/chem.201102782] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Indexed: 11/10/2022]
Abstract
5-Formylcytosine (fC or (5-CHO)dC) and 5-carboxylcytosine (caC or (5-COOH)dC) have recently been identified as constituents of mammalian DNA. The nucleosides are formed from 5-methylcytosine (mC or (5-Me)dC) via 5-hydroxymethylcytosine (hmC or (5-HOMe)dC) and are possible intermediates of an active DNA demethylation process. Here we show efficient syntheses of phosphoramidites which enable the synthesis of DNA strands containing these cytosine modifications based on Pd(0)-catalyzed functionalization of 5-iododeoxycytidine. The first crystal structure of fC reveals the existence of an intramolecular H-bond between the exocyclic amine and the formyl group, which controls the conformation of the formyl substituent. Using a newly designed in vitro mutagenicity assay we show that fC and caC are only marginally mutagenic, which is a prerequisite for the bases to function as epigenetic control units.
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Affiliation(s)
- Martin Münzel
- Center for Integrated Protein Science (CiPSM) at the Department of Chemistry, Ludwig-Maximilians-University, Butenandtstr. 5-13, 81377 Munich, Germany
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23
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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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