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Tian C, Yamashita S, Kimura A, Obata Y, Yu H, Taguchi M. Hydroxyl radical scavenging and chemical repair capabilities of positively charged peptides (PCPs): a pulse radiolysis study. Free Radic Res 2024; 58:388-395. [PMID: 39113587 DOI: 10.1080/10715762.2024.2385342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 06/20/2024] [Accepted: 07/16/2024] [Indexed: 08/20/2024]
Abstract
Pulse radiolysis was employed to investigate fundamental radiation chemical reactions, which are essential in the radiation protection of DNA. Two positively charged peptides (PCPs), histidine-tyrosine-histidine (His-Tyr-His) and lysine-tyrosine-lysine (Lys-Tyr-Lys), as well as the amino acids that constitute them, were involved. The reaction rate constants for tyrosine (Tyr), histidine (His), lysine (Lys), His-Tyr-His, and Lys-Tyr-Lys with OH radicals (•OH) were (1.6 ± 0.3) × 1010, (9.0 ± 0.9) × 109, (1.4 ± 0.3) × 109, (1.8 ± 0.1) × 1010, and (1.0 ± 0.1) × 1010 M-1s-1, respectively, indicating that formation of peptide bond can affect the reaction of amino acids with •OH. Observed transient absorption spectra indicated a shielding effect of the His or Lys residues at both ends of the PCPs on the centrally located Tyr. The measurement of chemical repair capabilities using deoxyguanosine monophosphate (dGMP) as a model for DNA demonstrated that the reaction rate constants of Tyr, His-Tyr-His, and Lys-Tyr-Lys with dGMP radicals were (2.2 ± 0.5) × 108, (2.3 ± 0.1) × 108, and (3.3 ± 0.4) × 108 M-1s-1, respectively, implying that the presence of a positive charge may enhance the chemical repair process.
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Affiliation(s)
- Chaozhong Tian
- Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Tokyo, Japan
| | - Shinichi Yamashita
- Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Tokyo, Japan
- Nuclear Professional School, School of Engineering, The University of Tokyo, Naka-gun, Japan
| | - Atsushi Kimura
- National Institutes for Quantum Science and Technology (QST), Takasaki Institute for Advanced Quantum Science, Takasaki, Japan
| | - Yui Obata
- Nuclear Professional School, School of Engineering, The University of Tokyo, Naka-gun, Japan
| | - Hao Yu
- National Institutes for Quantum Science and Technology (QST), Takasaki Institute for Advanced Quantum Science, Takasaki, Japan
| | - Mitsumasa Taguchi
- National Institutes for Quantum Science and Technology (QST), Takasaki Institute for Advanced Quantum Science, Takasaki, Japan
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Oikeh E, Ziebarth J, Dinar MAM, Kirchhoff D, Aronova A, Dziubla TD, Wang Y, DeRouchey JE. DNA Packaging and Polycation Length Determine DNA Susceptibility to Free Radical Damage in Condensed DNA. J Phys Chem B 2024; 128:3329-3339. [PMID: 38557033 DOI: 10.1021/acs.jpcb.3c06116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
In nature, DNA exists primarily in a highly compacted form. The compaction of DNA in vivo is mediated by cationic proteins: histones in somatic nuclei and protamines in sperm chromatin. The extreme, nearly crystalline packaging of DNA by protamines in spermatozoa is thought to be essential for both efficient genetic delivery as well as DNA protection against damage by mutagens and oxidative species. The protective role of protamines is required in sperm, as they are sensitive to ROS damage due to the progressive loss of DNA repair mechanisms during maturation. The degree to which DNA packaging directly relates to DNA protection in the condensed state, however, is poorly understood. Here, we utilized different polycation condensing agents to achieve varying DNA packaging densities and quantify DNA damage by free radical oxidation within the condensates. Although we see that tighter DNA packaging generally leads to better protection, the length of the polycation also plays a significant role. Molecular dynamics simulations suggest that longer polyarginine chains offer increased protection by occupying more space on the DNA surface and forming more stable interactions. Taken together, our results suggest a complex interplay among polycation properties, DNA packaging density, and DNA protection against free radical damage within condensed states.
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Affiliation(s)
- Ehigbai Oikeh
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Jesse Ziebarth
- Department of Chemistry, University of Memphis, Memphis, Tennessee 38152, United States
| | - Md Abu Monsur Dinar
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Daniel Kirchhoff
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Anastasiia Aronova
- Chemical and Materials Engineering Department, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Thomas D Dziubla
- Chemical and Materials Engineering Department, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Yongmei Wang
- Department of Chemistry, University of Memphis, Memphis, Tennessee 38152, United States
| | - Jason E DeRouchey
- Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States
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4
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Lee JH, Kim EW, Croteau DL, Bohr VA. Heterochromatin: an epigenetic point of view in aging. Exp Mol Med 2020; 52:1466-1474. [PMID: 32887933 PMCID: PMC8080806 DOI: 10.1038/s12276-020-00497-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 06/08/2020] [Accepted: 06/15/2020] [Indexed: 12/19/2022] Open
Abstract
Aging is an inevitable process of life. Defined by progressive physiological and functional loss of tissues and organs, aging increases the risk of mortality for the organism. The aging process is affected by various factors, including genetic and epigenetic ones. Here, we review the chromatin-specific epigenetic changes that occur during normal (chronological) aging and in premature aging diseases. Taking advantage of the reversible nature of epigenetic modifications, we will also discuss possible lifespan expansion strategies through epigenetic modulation, which was considered irreversible until recently.
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Affiliation(s)
- Jong-Hyuk Lee
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD, 21224, USA
| | - Edward W Kim
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD, 21224, USA
| | - Deborah L Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD, 21224, USA
| | - Vilhelm A Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD, 21224, USA. .,Danish Center for Healthy Aging, University of Copenhagen, 2200, Copenhagen, Denmark.
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Lee JH, Demarest TG, Babbar M, Kim EW, Okur MN, De S, Croteau DL, Bohr VA. Cockayne syndrome group B deficiency reduces H3K9me3 chromatin remodeler SETDB1 and exacerbates cellular aging. Nucleic Acids Res 2019; 47:8548-8562. [PMID: 31276581 DOI: 10.1093/nar/gkz568] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 06/09/2019] [Accepted: 06/29/2019] [Indexed: 12/30/2022] Open
Abstract
Cockayne syndrome is an accelerated aging disorder, caused by mutations in the CSA or CSB genes. In CSB-deficient cells, poly (ADP ribose) polymerase (PARP) is persistently activated by unrepaired DNA damage and consumes and depletes cellular nicotinamide adenine dinucleotide, which leads to mitochondrial dysfunction. Here, the distribution of poly (ADP ribose) (PAR) was determined in CSB-deficient cells using ADPr-ChAP (ADP ribose-chromatin affinity purification), and the results show striking enrichment of PAR at transcription start sites, depletion of heterochromatin and downregulation of H3K9me3-specific methyltransferases SUV39H1 and SETDB1. Induced-expression of SETDB1 in CSB-deficient cells downregulated PAR and normalized mitochondrial function. The results suggest that defects in CSB are strongly associated with loss of heterochromatin, downregulation of SETDB1, increased PAR in highly-transcribed regions, and mitochondrial dysfunction.
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Affiliation(s)
- Jong-Hyuk Lee
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Tyler G Demarest
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Mansi Babbar
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Edward W Kim
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Mustafa N Okur
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Supriyo De
- Laboratory of Genetics and Genomics, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Deborah L Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Vilhelm A Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.,Danish Center for Healthy Aging, University of Copenhagen, 2200 Copenhagen, Denmark
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Razskazovskiy Y, Tegomoh M, Roginskaya M. Association with Polyamines and Polypeptides Increases the Relative Yield of 2-Deoxyribonolactone Lesions in Radiation-Damaged DNA. Radiat Res 2019; 192:324-330. [DOI: 10.1667/rr15396.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
| | - Modeste Tegomoh
- Departments of Chemistry, East Tennessee State University, Johnson City, Tennessee 37614
| | - Marina Roginskaya
- Departments of Chemistry, East Tennessee State University, Johnson City, Tennessee 37614
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An R, Dong P, Komiyama M, Pan X, Liang X. Inhibition of nonenzymatic depurination of nucleic acids by polycations. FEBS Open Bio 2017; 7:1707-1714. [PMID: 29123979 PMCID: PMC5666391 DOI: 10.1002/2211-5463.12308] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 08/08/2017] [Accepted: 08/24/2017] [Indexed: 11/11/2022] Open
Abstract
DNA base depurination is one of the most common forms of DNA damage in vivo and in vitro, and the suppression of depurination is very important for versatile applications of DNA in biotechnology and medicine. In this work, it was shown that the polycations chitosan (Cho) and spermine (Spm) strongly inhibit DNA depurination through the formation of polyion complexes with DNA molecules. The intramolecular electrostatic interaction of positively charged polycations with DNA efficiently suppresses the protonation of purine groups, which is the key step of depurination. Importantly, the optimal pH for Cho's inhibition of depurination is significantly different from that of Spm. Cho is very effective in the inhibition of depurination in highly acidic media (pH: 1.5–3), whereas Spm is found to suppress the chemical reaction near neutral pH, as well as in acidic solutions. This remarkable pH specificity of the two biorelevant polycations is attributed to the difference in the pKa values of the amino groups. The relevance of our results with the biological roles of biogenic polycations is also discussed.
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Affiliation(s)
- Ran An
- College of Food Science and Engineering Ocean University of China Qingdao China.,Laboratory for Marine Drugs and Bioproducts Qingdao National Laboratory for Marine Science and Technology China
| | - Ping Dong
- College of Food Science and Engineering Ocean University of China Qingdao China
| | - Makoto Komiyama
- College of Food Science and Engineering Ocean University of China Qingdao China.,National Institute for Materials Science (NIMS) Tsukuba Japan
| | - Xiaoming Pan
- College of Food Science and Engineering Ocean University of China Qingdao China
| | - Xingguo Liang
- College of Food Science and Engineering Ocean University of China Qingdao China.,Laboratory for Marine Drugs and Bioproducts Qingdao National Laboratory for Marine Science and Technology China
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Øyen LF, Aalbergsjø SG, Knudtsen IS, Hole EO, Sagstuen E. Direct radiation effects to the amino acid side chain: EMR and periodic DFT of X-irradiated L-asparagine at 6 K. J Phys Chem B 2015; 119:491-502. [PMID: 25514178 DOI: 10.1021/jp5115866] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Radical formation in single crystals of L-asparagine monohydrate following X-irradiation at 6 K has been investigated at 6 K and at elevated temperatures using various electron magnetic resonance (EMR) techniques such as electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopy. Molecular structures of the three free radicals stable at 6 K were assessed by detailed analysis of the experimental data and density functional theory (DFT) calculations in a periodic approach. Radical LI is assumed to result from one-electron reduction at the amide functional group in the asparagine side chain followed by protonation at the amide carbonyl oxygen by proton transfer from a neighboring molecule across a hydrogen bond. Radical LII is assigned to a one-electron reduction of the carboxyl group in the amino acid backbone, followed by proton transfer across a hydrogen bond between a carboxylic oxygen and a neighboring asparagine molecule. Radical LIII is suggested to be formed by a net CO2 abstraction from an initial one-electron oxidized amino acid backbone. For the DFT modeling of LIII at 6 K, it was chosen to include the CO2 group stably embedded in the crystalline lattice. The assignments made are discussed in relation to previous work on L-asparagine. The relevance of these results to possible charge transfer processes in protein:DNA complexes is discussed.
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Affiliation(s)
- Live F Øyen
- Department of Physics, University of Oslo , P.O. Box 1048, Blindern, N-0316 Oslo, Norway
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Knudtsen IS, Aalbergsjø SG, Hole EO, Sagstuen E. Radiation effects on crystalline l-asparagine, revisited: Radical formation by EMR and periodic DFT after X-irradiation at 275K. Radiat Phys Chem Oxf Engl 1993 2015. [DOI: 10.1016/j.radphyschem.2014.07.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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10
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Iacomino G, Picariello G, Stillitano I, D'Agostino L. Nuclear aggregates of polyamines in a radiation-induced DNA damage model. Int J Biochem Cell Biol 2013; 47:11-9. [PMID: 24291171 DOI: 10.1016/j.biocel.2013.11.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 10/24/2013] [Accepted: 11/12/2013] [Indexed: 01/04/2023]
Abstract
Polyamines (PA) are believed to protect DNA minimizing the effect of radiation damage either by inducing DNA compaction and aggregation or acting as scavengers of free radicals. Using an in vitro pDNA double strand breakage assay based on gel electrophoretic mobility, we compared the protective capability of PA against γ-radiation with that of compounds generated by the supramolecular self-assembly of nuclear polyamines and phosphates, named Nuclear Aggregates of Polyamines (NAPs). Both unassembled PA and in vitro produced NAPs (ivNAPs) were ineffective in conferring pDNA protection at the sub-mM concentration. Single PA showed an appreciable protective effect only at high (mM) concentrations. However, concentrations of spermine (4+) within a critical range (0.481 mM) induced pDNA precipitation, an event that was not observed with NAPs-pDNA interaction. We conclude that the interaction of individual PA is ineffective to assure DNA protection, simultaneously preserving the flexibility and charge density of the double strand. Furthermore, data obtained by testing polyamine and ivNAPS with the current radiation-induced DNA damage model support the concept that PA-phosphate aggregates are the only forms through which PA interact with DNA.
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Lee M, Urata SM, Aguilera JA, Perry CC, Milligan JR. Modeling the Influence of Histone Proteins on the Sensitivity of DNA to Ionizing Radiation. Radiat Res 2012; 177:152-63. [DOI: 10.1667/rr2812.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Sharma KKK, Tyagi R, Purkayastha S, Bernhard WA. One-electron oxidation of DNA by ionizing radiation: competition between base-to-base hole-transfer and hole-trapping. J Phys Chem B 2010; 114:7672-80. [PMID: 20469885 DOI: 10.1021/jp101717u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The distance of hole migration through DNA determines the degree to which radiation-induced lesions are clustered. It is the degree of clustering that confers to ionizing radiation its high toxicity. The migration distance is governed by a competition between hole transfer and irreversible trapping reactions. An important type of trapping is reactions that lead to the formation of deoxyribose radicals, which are precursors to free base release (fbr). Using HPLC, fbr was measured in X-irradiated films of d(CGCGCGCGCG)(2) and d(CGCGAATTCGCG)(2) as well as three genomic DNAs: M. luteus, calf thymus, and C. perfringens. The level of DNA hydration was varied from Gamma = 2.5 to 22 mol waters/mol nucleotide. The chemical yields of each base, G(base), were measured and used to calculate the modification factor, M(base). This factor compensates for differences in the GC/AT ratio, providing a measure of the degree to which a given base influences its own release. In the DNA oligomers, M(Gua) > M(Cyt), a result ascribed to the previously observed end effect in short oligomers. In the highly polymerized genomic DNA, we found that M(Cyt) > M(Gua) and that M(Thy) is consistently the smallest of the M factors. For these same DNA films, the yields of total DNA trapped radicals, G(tot)(fr), were measured using EPR spectroscopy. The yield of deoxyribose radicals was calculated using G(dRib)(fr) = approximately 0.11 x G(tot)(fr). Comparing G(dRib)(fr) with total fbr, we found that only about half of the fbr is accounted for by deoxyribose radical intermediates. We conclude that for a hole on cytosine, Cyt(*+), base-to-base hole transfer competes with irreversible trapping by the deoxyribose. In the case of a hole on thymine, Thy(*+), base-to-base hole transfer competes with irreversible trapping by methyl deprotonation. Close proximity of Gua protects the deoxyribose of Cyt but sensitizes the deoxyribose of Thy.
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Affiliation(s)
- Kiran K K Sharma
- Department of Biochemistry & Biophysics, University of Rochester, Rochester, New York 14642, USA
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Ptasińska S, Li Z, Mason NJ, Sanche L. Damage to amino acid-nucleotide pairs induced by 1 eV electrons. Phys Chem Chem Phys 2010; 12:9367-72. [PMID: 20563347 PMCID: PMC3828173 DOI: 10.1039/b926267a] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated the role of two selected amino acids, glycine and arginine, on damage induced to a short chain of single stranded DNA, the tetramer GCAT, during 1 eV electron exposure. At this energy, DNA has a high cross section for DNA damage via exclusively dissociative electron attachment. Surprisingly, at low ratios of glycine:GCAT, an increase in the total fragmentation yield is observed, whilst at higher ratios, glycine and arginine appear to protect DNA from the direct action of electrons. In addition, binding energies were calculated by molecular modelling of the interactions between these amino acids and either nucleobases or nucleotides. These binding energies appear to be related to the ability of amino acids to protect DNA against low energy electron damage.
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Affiliation(s)
- Sylwia Ptasińska
- Department of Physics & Astronomy, The Open University, Milton Keynes, UK MK7 6AA.
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Sharma KKK, Bernhard WA. Direct damage to the backbone of DNA oligomers is influenced by the OH moiety at strand ends, by the type of base, and by context. J Phys Chem B 2009; 113:12839-43. [PMID: 19722540 DOI: 10.1021/jp905750w] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Previous studies on high molecular weight DNA found that backbone damage, as monitored by free base release, is relatively independent of the type of base; i.e., the yields of all four bases were nearly equal. This could be due to a lack of influence of any given base over damage to its own deoxyribose or it could be a consequence of averaging out disparities due to each base sampling a wide range of base contexts. This study is aimed at distinguishing between these two possibilities. Transparent films, prepared from palindromic oligodeoxynucleotides of d(CTCTCGAGAG), d(CTCTCGAGAGp), d(pCTCTCGAGAGp), d(GAGAGCTCTC), d(ACGCGCGCGT), d(AACGCGCGCGTT), d(CTCTCTTAATAATTATAATTATTAAGAGAG), and d(CTCTCTTAATATTAAGAGAG), were used for this investigation. The DNA films, hydrated to approximately 2.5 waters per nucleotide, were irradiated at RT under air using X-rays generated by a tungsten tube, immediately dissolved in nuclease-free water, and stored at 277 K for 24 h, and then unaltered free base release was measured using HPLC. Yields of free base release were based on a target mass consisting of the DNA and one counterion+2.5 H2O/nucleotide. The yields of each base, G(C), G(G), G(T), and G(A) were determined for each of the above sequences. The observed yields lead to the following conclusions: (i) base release at the oligomer ends is favored over release at internal positions (called the end effect), (ii) phosphorylation of the OH moiety at the oligomer ends quenches the end effect, (iii) the magnitude of the end effect is influenced by the base at the end and the bases proximal to it, and (iv) the release of base is influenced by the base and its context.
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Affiliation(s)
- Kiran Kumar K Sharma
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA
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Ptasińska S, Stypczyńska A, Nixon T, Mason NJ, Klyachko DV, Sanche L. X-ray induced damage in DNA monitored by X-ray photoelectron spectroscopy. J Chem Phys 2008; 129:065102. [DOI: 10.1063/1.2961027] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Sharma KK, Purkayastha S, Bernhard WA. Unaltered free base release from d(CGCGCG)2 produced by the direct effect of ionizing radiation at 4 K and room temperature. Radiat Res 2007; 167:501-7. [PMID: 17474798 PMCID: PMC2603164 DOI: 10.1667/rr0847.1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Accepted: 12/15/2006] [Indexed: 11/03/2022]
Abstract
Unaltered free base release in d(CGCGCG)2 exposed to X rays at 4 K or room temperature was measured by HPLC. Samples were prepared either as films hydrated to a level of Gamma = 2.5 mol water/mol nucleotide or as polycrystalline with Gamma approximately 7.5 mol water/mol nucleotide. X irradiation of films at 4 K, followed by annealing to room temperature, resulted in yields for cytosine and guanine of G(Cyt) = 0.036 +/- 0.001 micromol/J and G(Gua) = 0.090 +/- 0.002 micromol/J. Irradiation of films at room temperature gave similar yields. The yields for polycrystalline d(CGCGCG)2 X-irradiated at room temperature were G(Cyt) = 0.035 +/- 0.005 micromol/J and G(Gua) = 0.077 +/- 0.023 micromol/J. The total free base release yield, G(fbr), was 0.124 +/- 0.008 micromol/J for films and 0.112 +/- 0.028 micromol/J for polycrystalline samples. G(fbr) is believed to be a good estimate of total strand break yield. The yields of total free radicals trapped [G(Sigmafr)] by the d(CGCGCG)2 films at 4 K were measured by EPR. The measured value, G(Sigmafr) = 0.450 +/- 0.005 micromol/J, was used to calculate the yield of trappable sugar radicals, giving G(sugar)(fr) = 0.04-0.07 micromol/J. We found that (1) guanine release exceeded cytosine release by more than twofold, (2) G(sugar)(fr) cannot account for more than half of the free base release, and (3) G(fbr), G(Cyt) and G(Gua) were independent of the sample temperature during irradiation. Finding (1) suggests that base and or sequence influences sugar damage, and finding (2) is consistent with our working hypothesis that an important pathway to strand break formation entails two one-electron oxidations at the same sugar site.
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Affiliation(s)
- Kiran K Sharma
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA
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