Absorption of Low-Energy UV Radiation by Human Telomere G-Quadruplexes Generates Long-Lived Guanine Radical Cations

Akos Banyasz 1, 2 Lara Martinez-Fernandez 3 Clémence Balty 2, 1 Marion Perron 4 Thierry Douki 5 Roberto Improta 3 Dimitra Markovitsi 2, 1
1 DICO - Biomolécules Excitées
IRAMIS - Institut Rayonnement Matière de Saclay, LIDyl - Laboratoire Interactions, Dynamique et Lasers (ex SPAM)
5 CIBEST - Chimie Interface Biologie pour l’Environnement, la Santé et la Toxicologie
SYMMES - SYstèmes Moléculaires et nanoMatériaux pour l’Energie et la Santé : DRF/INAC/SYMMES
Abstract : Telomeres, which are involved in cell division, carcinogenesis, and aging and constitute important therapeutic targets, are prone to oxidative damage. This propensity has been correlated with the presence of guanine-rich sequences, capable of forming four-stranded DNA structures (G-quadruplexes). Here, we present the first study on oxidative damage of human telomere G-quadruplexes without mediation of external molecules. Our investigation has been performed for G-quadruplexes formed by folding of GGG(TTAGGG)3 single strands in buffered solutions containing Na+ cations (TEL21/Na+). Associating nanosecond time-resolved spectroscopy and quantum mechanical calculations (TD-DFT), it focuses on the primary species, ejected electrons and guanine radicals, generated upon absorption of UV radiation directly by TEL21/Na+. We show that, at 266 nm, corresponding to an energy significantly lower than the guanine ionization potential, the one-photon ionization quantum yield is 4.5 × 10–3. This value is comparable to that of cyclobutane thymine dimers (the major UV-induced lesions) in genomic DNA; the quantum yield of these dimers in TEL21/Na+ is found to be (1.1 ± 0.1) × 10–3. The fate of guanine radicals, generated in equivalent concentration with that of ejected electrons, is followed over 5 orders of magnitude of time. Such a quantitative approach reveals that an important part of radical cation population survives up to a few milliseconds, whereas radical cations produced by chemical oxidants in various DNA systems are known to deprotonate, at most, within a few microseconds. Under the same experimental conditions, neither one-photon ionization nor long-lived radical cations are detected for the telomere repeat TTAGGG in single-stranded configuration, showing that secondary structure plays a key role in these processes. Finally, two types of deprotonated radicals are identified: on the one hand, (G-H2)• radicals, stable at early times, and on the other hand, (G-H1)• radicals, appearing within a few milliseconds and decaying with a time constant of ∼50 ms.
Type de document :
Article dans une revue
Journal of the American Chemical Society, American Chemical Society, 2017, 139 (30), pp.10561 - 10568. 〈10.1021/jacs.7b05931〉
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Soumis le : mercredi 20 décembre 2017 - 14:34:40
Dernière modification le : jeudi 15 mars 2018 - 15:05:47

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Akos Banyasz, Lara Martinez-Fernandez, Clémence Balty, Marion Perron, Thierry Douki, et al.. Absorption of Low-Energy UV Radiation by Human Telomere G-Quadruplexes Generates Long-Lived Guanine Radical Cations. Journal of the American Chemical Society, American Chemical Society, 2017, 139 (30), pp.10561 - 10568. 〈10.1021/jacs.7b05931〉. 〈cea-01668999〉

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