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G-quadruplex folds of the human telomere sequence alter the site reactivity and reaction pathway of guanine oxidation compared to duplex DNA.
Chem Res Toxicol 2013; 26(4):593-607CR

Abstract

Telomere shortening occurs during oxidative and inflammatory stress with guanine (G) as the major site of damage. In this work, a comprehensive profile of the sites of oxidation and structures of products observed from G-quadruplex and duplex structures of the human telomere sequence was studied in the G-quadruplex folds (hybrid (K(+)), basket (Na(+)), and propeller (K(+) + 50% CH3CN)) resulting from the sequence 5'-(TAGGGT)4T-3' and in an appropriate duplex containing one telomere repeat. Oxidations with four oxidant systems consisting of riboflavin photosensitization, carbonate radical generation, singlet oxygen, and the copper Fenton-like reaction were analyzed under conditions of low product conversion to determine relative reactivity. The one-electron oxidants damaged the 5'-G in G-quadruplexes leading to spiroiminodihydantoin (Sp) and 2,2,4-triamino-2H-oxazol-5-one (Z) as major products as well as 8-oxo-7,8-dihydroguanine (OG) and 5-guanidinohydantoin (Gh) in low relative yields, while oxidation in the duplex context produced damage at the 5'- and middle-Gs of GGG sequences and resulted in Gh being the major product. Addition of the reductant N-acetylcysteine (NAC) to the reaction did not alter the riboflavin-mediated damage sites but decreased Z by 2-fold and increased OG by 5-fold, while not altering the hydantoin ratio. However, NAC completely quenched the CO3(•-) reactions. Singlet oxygen oxidations of the G-quadruplex showed reactivity at all Gs on the exterior faces of G-quartets and furnished the product Sp, while no oxidation was observed in the duplex context under these conditions, and addition of NAC had no effect. Because a long telomere sequence would have higher-order structures of G-quadruplexes, studies were also conducted with 5'-(TAGGGT)8-T-3', and it provided oxidation profiles similar to those of the single G-quadruplex. Lastly, Cu(II)/H2O2-mediated oxidations were found to be indiscriminate in the damage patterns, and 5-carboxamido-5-formamido-2-iminohydantoin (2Ih) was found to be a major duplex product, while nearly equal yields of 2Ih and Sp were observed in G-quadruplex contexts. These findings indicate that the nature of the secondary structure of folded DNA greatly alters both the reactivity of G toward oxidative stress as well as the product outcome and suggest that recognition of damage in telomeric sequences by repair enzymes may be profoundly different from that of B-form duplex DNA.

Authors+Show Affiliations

Department of Chemistry, University of Utah , 315 South 1400 East, Salt Lake City, Utah 84112-0850, United States.No affiliation info available

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural

Language

eng

PubMed ID

23438298

Citation

Fleming, Aaron M., and Cynthia J. Burrows. "G-quadruplex Folds of the Human Telomere Sequence Alter the Site Reactivity and Reaction Pathway of Guanine Oxidation Compared to Duplex DNA." Chemical Research in Toxicology, vol. 26, no. 4, 2013, pp. 593-607.
Fleming AM, Burrows CJ. G-quadruplex folds of the human telomere sequence alter the site reactivity and reaction pathway of guanine oxidation compared to duplex DNA. Chem Res Toxicol. 2013;26(4):593-607.
Fleming, A. M., & Burrows, C. J. (2013). G-quadruplex folds of the human telomere sequence alter the site reactivity and reaction pathway of guanine oxidation compared to duplex DNA. Chemical Research in Toxicology, 26(4), pp. 593-607. doi:10.1021/tx400028y.
Fleming AM, Burrows CJ. G-quadruplex Folds of the Human Telomere Sequence Alter the Site Reactivity and Reaction Pathway of Guanine Oxidation Compared to Duplex DNA. Chem Res Toxicol. 2013 Apr 15;26(4):593-607. PubMed PMID: 23438298.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - G-quadruplex folds of the human telomere sequence alter the site reactivity and reaction pathway of guanine oxidation compared to duplex DNA. AU - Fleming,Aaron M, AU - Burrows,Cynthia J, Y1 - 2013/03/13/ PY - 2013/2/27/entrez PY - 2013/2/27/pubmed PY - 2014/9/27/medline SP - 593 EP - 607 JF - Chemical research in toxicology JO - Chem. Res. Toxicol. VL - 26 IS - 4 N2 - Telomere shortening occurs during oxidative and inflammatory stress with guanine (G) as the major site of damage. In this work, a comprehensive profile of the sites of oxidation and structures of products observed from G-quadruplex and duplex structures of the human telomere sequence was studied in the G-quadruplex folds (hybrid (K(+)), basket (Na(+)), and propeller (K(+) + 50% CH3CN)) resulting from the sequence 5'-(TAGGGT)4T-3' and in an appropriate duplex containing one telomere repeat. Oxidations with four oxidant systems consisting of riboflavin photosensitization, carbonate radical generation, singlet oxygen, and the copper Fenton-like reaction were analyzed under conditions of low product conversion to determine relative reactivity. The one-electron oxidants damaged the 5'-G in G-quadruplexes leading to spiroiminodihydantoin (Sp) and 2,2,4-triamino-2H-oxazol-5-one (Z) as major products as well as 8-oxo-7,8-dihydroguanine (OG) and 5-guanidinohydantoin (Gh) in low relative yields, while oxidation in the duplex context produced damage at the 5'- and middle-Gs of GGG sequences and resulted in Gh being the major product. Addition of the reductant N-acetylcysteine (NAC) to the reaction did not alter the riboflavin-mediated damage sites but decreased Z by 2-fold and increased OG by 5-fold, while not altering the hydantoin ratio. However, NAC completely quenched the CO3(•-) reactions. Singlet oxygen oxidations of the G-quadruplex showed reactivity at all Gs on the exterior faces of G-quartets and furnished the product Sp, while no oxidation was observed in the duplex context under these conditions, and addition of NAC had no effect. Because a long telomere sequence would have higher-order structures of G-quadruplexes, studies were also conducted with 5'-(TAGGGT)8-T-3', and it provided oxidation profiles similar to those of the single G-quadruplex. Lastly, Cu(II)/H2O2-mediated oxidations were found to be indiscriminate in the damage patterns, and 5-carboxamido-5-formamido-2-iminohydantoin (2Ih) was found to be a major duplex product, while nearly equal yields of 2Ih and Sp were observed in G-quadruplex contexts. These findings indicate that the nature of the secondary structure of folded DNA greatly alters both the reactivity of G toward oxidative stress as well as the product outcome and suggest that recognition of damage in telomeric sequences by repair enzymes may be profoundly different from that of B-form duplex DNA. SN - 1520-5010 UR - https://www.unboundmedicine.com/medline/citation/23438298/G_quadruplex_folds_of_the_human_telomere_sequence_alter_the_site_reactivity_and_reaction_pathway_of_guanine_oxidation_compared_to_duplex_DNA_ L2 - https://dx.doi.org/10.1021/tx400028y DB - PRIME DP - Unbound Medicine ER -