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Jang EK, Koike Y, Ide Y, Tajima K, Kanaori K, Pack SP. Nucleobase-involved native chemical ligation: a novel reaction between an oxanine nucleobase and N-terminal cysteine for oligonucleotide-peptide conjugation. Chem Commun (Camb) 2020; 56:5508-5511. [PMID: 32296789 DOI: 10.1039/c9cc08808c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
In bioconjugation chemistry, achieving a target-specific reaction for a non-modified amino acid is challenging. Here, we report a novel nucleobase-involved native chemical ligation (NbCL) that allows a site-specific oligonucleotide-peptide conjugation via a new S-N acyl transfer reaction between an oxanine nucleobase and N-terminal cysteine.
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Affiliation(s)
- Eui Kyoung Jang
- Department of Biotechnology and Bioinformatics, Korea University, Sejong-Ro 2511, Sejong, 30019, Republic of Korea.
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Jang EK, Son RG, Pack SP. Novel enzymatic single-nucleotide modification of DNA oligomer: prevention of incessant incorporation of nucleotidyl transferase by ribonucleotide-borate complex. Nucleic Acids Res 2019; 47:e102. [PMID: 31318972 PMCID: PMC6753491 DOI: 10.1093/nar/gkz612] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 06/17/2019] [Accepted: 07/06/2019] [Indexed: 12/16/2022] Open
Abstract
Terminal deoxynucleotidyl transferase (TdT), which mediates template-independent polymerization with low specificity for nucleotides, has been used for nucleotide extension of DNA oligomers. One concern is that it is difficult to control the number of incorporated nucleotides, which is a limitation on the use of TdT for single-nucleotide incorporation of DNA oligomers. Herein, we uncovered an interesting inhibitory effect on TdT when ribonucleotide substrates (rNTPs) were employed in a borate buffer. On the basis of unique inhibitory effects of the ribonucleotide-borate complex, we developed a novel enzymatic method for single-nucleotide incorporation of a DNA oligomer with a modified rNTP by TdT. Single-nucleotide incorporation of a DNA oligomer with various modified rNTPs containing an oxanine, biotin, aminoallyl or N6-propargyl group was achieved with a high yield. The 'TdT in rNTP-borate' method is quite simple and efficient for preparing a single-nucleotide modified DNA oligomer, which is useful for the design of functional DNA-based systems.
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Affiliation(s)
- Eui Kyoung Jang
- Department of Biotechnology and Bioinformatics, Korea University, Sejong-Ro 2511, Sejong 30019, Republic of Korea
| | - Ryeo Gang Son
- Department of Biotechnology and Bioinformatics, Korea University, Sejong-Ro 2511, Sejong 30019, Republic of Korea
| | - Seung Pil Pack
- Department of Biotechnology and Bioinformatics, Korea University, Sejong-Ro 2511, Sejong 30019, Republic of Korea
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Design of reactive-end DNA oligomers via incorporation of oxanine into oligonucleotides using terminal deoxynucleotidyl transferase. Process Biochem 2017. [DOI: 10.1016/j.procbio.2017.07.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Nakano T, Miyamoto-Matsubara M, Shoulkamy MI, Salem AMH, Pack SP, Ishimi Y, Ide H. Translocation and stability of replicative DNA helicases upon encountering DNA-protein cross-links. J Biol Chem 2013; 288:4649-58. [PMID: 23283980 DOI: 10.1074/jbc.m112.419358] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA-protein cross-links (DPCs) are formed when cells are exposed to various DNA-damaging agents. Because DPCs are extremely large, steric hindrance conferred by DPCs is likely to affect many aspects of DNA transactions. In DNA replication, DPCs are first encountered by the replicative helicase that moves at the head of the replisome. However, little is known about how replicative helicases respond to covalently immobilized protein roadblocks. In the present study we elucidated the effect of DPCs on the DNA unwinding reaction of hexameric replicative helicases in vitro using defined DPC substrates. DPCs on the translocating strand but not on the nontranslocating strand impeded the progression of the helicases including the phage T7 gene 4 protein, simian virus 40 large T antigen, Escherichia coli DnaB protein, and human minichromosome maintenance Mcm467 subcomplex. The impediment varied with the size of the cross-linked proteins, with a threshold size for clearance of 5.0-14.1 kDa. These results indicate that the central channel of the dynamically translocating hexameric ring helicases can accommodate only small proteins and that all of the helicases tested use the steric exclusion mechanism to unwind duplex DNA. These results further suggest that DPCs on the translocating and nontranslocating strands constitute helicase and polymerase blocks, respectively. The helicases stalled by DPC had limited stability and dissociated from DNA with a half-life of 15-36 min. The implications of the results are discussed in relation to the distinct stabilities of replisomes that encounter tight but reversible DNA-protein complexes and irreversible DPC roadblocks.
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Affiliation(s)
- Toshiaki Nakano
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
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Nakano T, Ouchi R, Kawazoe J, Pack SP, Makino K, Ide H. T7 RNA polymerases backed up by covalently trapped proteins catalyze highly error prone transcription. J Biol Chem 2012; 287:6562-72. [PMID: 22235136 DOI: 10.1074/jbc.m111.318410] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
RNA polymerases (RNAPs) transcribe genes through the barrier of nucleoproteins and site-specific DNA-binding proteins on their own or with the aid of accessory factors. Proteins are often covalently trapped on DNA by DNA damaging agents, forming DNA-protein cross-links (DPCs). However, little is known about how immobilized proteins affect transcription. To elucidate the effect of DPCs on transcription, we constructed DNA templates containing site-specific DPCs and performed in vitro transcription reactions using phage T7 RNAP. We show here that DPCs constitute strong but not absolute blocks to in vitro transcription catalyzed by T7 RNAP. More importantly, sequence analysis of transcripts shows that RNAPs roadblocked not only by DPCs but also by the stalled leading RNAP become highly error prone and generate mutations in the upstream intact template regions. This contrasts with the transcriptional mutations induced by conventional DNA lesions, which are delivered to the active site or its proximal position in RNAPs and cause direct misincorporation. Our data also indicate that the trailing RNAP stimulates forward translocation of the stalled leading RNAP, promoting the translesion bypass of DPCs. The present results provide new insights into the transcriptional fidelity and mutual interactions of RNAPs that encounter persistent roadblocks.
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Affiliation(s)
- Toshiaki Nakano
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
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Pack SP, Morimoto H, Makino K, Tajima K, Kanaori K. Solution structure and stability of the DNA undecamer duplexes containing oxanine mismatch. Nucleic Acids Res 2011; 40:1841-55. [PMID: 22039100 PMCID: PMC3287195 DOI: 10.1093/nar/gkr872] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Solution structures of DNA duplexes containing oxanine (Oxa, O) opposite a cytosine (O:C duplex) and opposite a thymine (O:T duplex) have been solved by the combined use of 1H NMR and restrained molecular dynamics calculation. One mismatch pair was introduced into the center of the 11-mer duplex of [d(GTGACO6CACTG)/d(CAGTGX17GTCAC), X = C or T]. 1H NMR chemical shifts and nuclear Overhauser enhancement (NOE) intensities indicate that both the duplexes adopt an overall right-handed B-type conformation. Exchangeable resonances of C17 4-amino proton of the O:C duplex and of T17 imino proton of O:T duplex showed unusual chemical shifts, and disappeared with temperature increasing up to 30°C, although the melting temperatures were >50°C. The O:C mismatch takes a wobble geometry with positive shear parameter where the Oxa ring shifted toward the major groove and the paired C17 toward the minor groove, while, in the O:T mismatch pair with the negative shear, the Oxa ring slightly shifted toward the minor groove and the paired T17 toward the major groove. The Oxa mismatch pairs can be wobbled largely because of no hydrogen bond to the O1 position of the Oxa base, and may occupy positions in the strands that optimize the stacking with adjacent bases.
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Affiliation(s)
- Seung Pil Pack
- Department of Biotechnology and Bioinformatics, Korea University, Jochiwon, Chungnam 339-700, Korea.
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Pack SP, Makino K. Synthesis of 2'-deoxyoxanosine from 2'-deoxyguanosine, conversion to its phosphoramidite, and incorporation into oxanine-containing oligodeoxynucleotides. ACTA ACUST UNITED AC 2010; Chapter 4:Unit 4.39. [PMID: 20517989 DOI: 10.1002/0471142700.nc0439s41] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Oxanine (Oxa, O) is one of the damaged bases produced from guanine (G) through nitrosative deamination induced by nitric oxide (NO) or nitrous acid (HNO(2)). Large-scale preparation of Oxa-containing oligodeoxynucleotide (Oxa-ODN) with the desired base sequence is a prerequisite for exploring detailed properties of Oxa in DNA. This can be accomplished by incubation of G nucleosides with NaNO(2) in acetic acid buffer (pH 3.5) to produce Oxa nucleosides (e.g., 2'-deoxyoxanosine or dOxo), conversion of dOxo to DMT-dOxo-amidite by tritylation and conventional phosphoramidation, and subsequent synthesis of Oxa-ODN. The presence of Oxa in the synthetic ODN is confirmed by enzymatic digestion. Oxa-ODN is useful for analyzing the biochemical and biophysical properties of Oxa in DNA, which is believed to be involved in NO-induced genotoxicity and cytotoxicity. In addition, since Oxa possesses the carbodiimide-activated carboxylate function (O-acylisourea structure), Oxa-ODN can be used as a functional DNA oligomer that makes covalent cross-linkages with amine or amine-containing biomolecules and amine-modified solid surfaces.
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Pack SP, Doi A, Choi YS, Kim HB, Makino K. Accurate guanine:cytosine discrimination in T4 DNA ligase-based single nucleotide polymorphism analysis using an oxanine-containing ligation fragment. Anal Biochem 2010; 398:257-9. [DOI: 10.1016/j.ab.2009.11.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2009] [Revised: 11/10/2009] [Accepted: 11/10/2009] [Indexed: 10/20/2022]
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Doi A, Pack SP, Makino K. Comparison of the molecular influences of NO-induced lesions in DNA strands on the reactivity of polynucleotide kinases, DNA ligases and DNA polymerases. J Biochem 2010; 147:697-703. [DOI: 10.1093/jb/mvq003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Pack SP, Doi A, Choi YS, Kodaki T, Makino K. Biomolecular response of oxanine in DNA strands to T4 polynucleotide kinase, T4 DNA ligase, and restriction enzymes. Biochem Biophys Res Commun 2010; 391:118-22. [DOI: 10.1016/j.bbrc.2009.11.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2009] [Accepted: 11/04/2009] [Indexed: 10/20/2022]
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Barone V, Cacelli I, Ferretti A, Monti S, Prampolini G. Parameterization and validation of an accurate force-field for the simulation of alkylamine functionalized silicon (111) surfaces. Phys Chem Chem Phys 2010; 12:4201-9. [DOI: 10.1039/b925041g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kamisetty NK, Pack SP, Nonogawa M, Yamada K, Yoshida Y, Kodaki T, Makino K. Stabilization of the immobilized linkers and DNA probes for DNA microarray fabrication by end-capping of the remaining unreacted silanol on the glass. J Biotechnol 2009; 140:242-5. [PMID: 19428719 DOI: 10.1016/j.jbiotec.2009.01.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2008] [Revised: 12/30/2008] [Accepted: 01/15/2009] [Indexed: 10/21/2022]
Abstract
High stability of the oligonucleotides immobilized on the glass is essential for the reliable DNA microarray analysis. In the present study, effect of end-capping of the unreacted silanol, remaining after the surface amine-functionalization, was explored: (1) Cy3-NHS (N-hydorxysuccinincimide) dye was spotted on the surface and change in the fluorescent intensity was measured. (2) DNA probes were immobilized by the reactivity of oxanine linked at the 5'-end, the complementary oligonucleotides with Cy5-fluorescence at the 5'-end was hybridized, and the time-dependence of the fluorescence intensity was observed. Both the systems showed improved stability of the immobilized molecules, indicative of the stabilization by end-capping.
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Barone V, Cacelli I, Ferretti A, Monti S, Prampolini G. Sensors for DNA detection: theoretical investigation of the conformational properties of immobilized single-strand DNA. Phys Chem Chem Phys 2009; 11:10644-56. [DOI: 10.1039/b914386f] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Pack SP, Doi A, Nonogawa M, Kamisetty NK, Devarayapalli KC, Kodaki T, Makino K. Biophysical stability and enzymatic recognition of oxanine in DNA. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2008; 26:1589-93. [PMID: 18066833 DOI: 10.1080/15257770701548295] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Oxanine (Oxa), which is one of the major products generated from guanine by nitrosative oxidation and is as long-lived as Gua in DNA, has been thought to be one of the major causes for NO-induced DNA damage. In the present study, using several synthetic Oxa-containing oligodeoxynucleotides, biophysical stability and enzymatic recognition of Oxa was investigated in DNA strands. It was found that Oxa did not mediate marked distortion in the whole DNA structure although Oxa pairing with 4 normal bases decreased thermal stability of the DNA duplexes compared to Gua:Cyt base pair. Regarding the responses of the DNA-relevant enzymes to Oxa, it was determined that Oxa was recognized as Gua except that DNA polymerases incorporated Thy as well as Cyt opposite Oxa. These results imply that Oxa tends to behave as a kind of naturally occurring base, Gua and therefore, would be involved in the genotoxic and cytotoxic threats of NO in cellular system.
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Affiliation(s)
- Seung Pil Pack
- Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
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Nucleotide excision repair and homologous recombination systems commit differentially to the repair of DNA-protein crosslinks. Mol Cell 2007; 28:147-58. [PMID: 17936711 DOI: 10.1016/j.molcel.2007.07.029] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Revised: 06/30/2007] [Accepted: 07/30/2007] [Indexed: 11/21/2022]
Abstract
DNA-protein crosslinks (DPCs)-where proteins are covalently trapped on the DNA strand-block the progression of replication and transcription machineries and hence hamper the faithful transfer of genetic information. However, the repair mechanism of DPCs remains largely elusive. Here we have analyzed the roles of nucleotide excision repair (NER) and homologous recombination (HR) in the repair of DPCs both in vitro and in vivo using a bacterial system. Several lines of biochemical and genetic evidence show that both NER and HR commit to the repair or tolerance of DPCs, but differentially. NER repairs DPCs with crosslinked proteins of sizes less than 12-14 kDa, whereas oversized DPCs are processed exclusively by RecBCD-dependent HR. These results highlight how NER and HR are coordinated when cells need to deal with unusually bulky DNA lesions such as DPCs.
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Pack SP, Kamisetty NK, Nonogawa M, Devarayapalli KC, Ohtani K, Yamada K, Yoshida Y, Kodaki T, Makino K. Direct immobilization of DNA oligomers onto the amine-functionalized glass surface for DNA microarray fabrication through the activation-free reaction of oxanine. Nucleic Acids Res 2007; 35:e110. [PMID: 17715142 PMCID: PMC2034461 DOI: 10.1093/nar/gkm619] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Oxanine having an O-acylisourea structure was explored to see if its reactivity with amino group is useful in DNA microarray fabrication. By the chemical synthesis, a nucleotide unit of oxanine (Oxa-N) was incorporated into the 5′-end of probe DNA with or without the -(CH2)n- spacers (n = 3 and 12) and found to immobilize the probe DNA covalently onto the NH2-functionalized glass slide by one-pot reaction, producing the high efficiency of the target hybridization. The methylene spacer, particularly the longer one, generated higher efficiency of the target recognition although there was little effect on the amount of the immobilized DNA oligomers. The post-spotting treatment was also carried out under the mild conditions (at 25 or 42°C) and the efficiencies of the immobilization and the target recognition were evaluated similarly, and analogous trends were obtained. It has also been determined under the mild conditions that the humidity and time of the post-spotting treatment, pH of the spotting solution and the synergistic effects with UV-irradiation largely contribute to the desired immobilization and resulting target recognition. Immobilization of DNA oligomer by use of Oxa-N on the NH2-functionalized surface without any activation step would be employed as one of the advanced methods for generating DNA-conjugated solid surface.
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Affiliation(s)
- Seung Pil Pack
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Nagendra Kumar Kamisetty
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Mitsuru Nonogawa
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Kamakshaiah Charyulu Devarayapalli
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Kairi Ohtani
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Kazunari Yamada
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Yasuko Yoshida
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Tsutomu Kodaki
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
| | - Keisuke Makino
- Institute of Advanced Energy, Kyoto University, CREST, JST (Japan Science and Technology Agency), Kyoto University, Gokasho, Uji 611-0011, NGK Insulators, Ltd, GENESHOT project, Mizuho, Nagoya 467-8530 and Kyoto Nanotechnology Cluster, Kyoto University, Gokasho, Uji 611-0011, Japan
- *To whom correspondence should be addressed. +81 774 38 3517+81 774 38 3524
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Beda NV, Nedospasov AA. NO-dependent modifications of nucleic acids. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2007; 33:195-228. [PMID: 17476982 DOI: 10.1134/s106816200702001x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
This review is devoted to chemical transformations of nucleic acids and their components under the action of nitrogen oxide metabolites. The deamination reaction of bases is discussed in the context of possible competing transformations of its intermediates (nitrosamines, diazonium cations, diazotates, triazenes, and diazoanhydrides) and mechanisms of crosslink formation with proteins and nucleic acids. The oxidation and nitration of bases by NO2 is considered together with the possibility of radical transfer to domains from the base stacks in DNA. Reduction of redox potentials of bases as a result of stacking interactions explains the possibility of their reactions within nucleic acids with the oxidants whose redox potential is insufficient for the effective reactions with mononucleotides. Modifications of nucleic acids with peroxynitrite derivatives are discussed in the context of the effect of the DNA primary structure and the modification products formed on the reactivity of single bases. The possibility of reduction of nitro groups within modified bases to amino derivatives and their subsequent diazotation is considered. The substitution of oxoguanine for nitroguanine residues may result; the reductive diazotation can lead to undamaged guanine. The intermediate modified bases, e.g., 8-aminoguanine and 8-diazoguanine, were shown to participate in noncanonical base pairing, including the formation of more stable bonds with two bases, which is characteristic of the DNA Z-form. A higher sensitivity of RNA in comparison with DNA to NO-dependent modifications (NODMs) is predicted on the basis of the contribution of medium microheterogeneity and the known mechanisms of nitrosylation and nitration. The possible biological consequences of nucleic acids NODMs are briefly considered. It is shown that the NODMs under the action of nitrogen oxide metabolites generated by macrophages and similar cells in inflammations or infections should lead to a sharp increase in the number of mutations in the case of RNA-containing viruses. As a result, the defense mechanisms of the host organism may contribute to the appearance of new, including more dangerous, variants of infecting viruses.
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