title: Interconversion of the cis-5R,6S- and trans-5R,6R-thymine glycol lesions in duplex DNA.
abstract: Thymine glycol (Tg), 5,6-dihydroxy-5,6-dihydrothymine, is formed in DNA by the reaction of thymine with reactive oxygen species. The 5R Tg lesion was incorporated site-specifically into 5'-d(G(1)T(2)G(3)C(4)G(5)Tg(6)G(7)T(8)T(9)T(10)G(11)T(12))-3'; Tg = 5R Tg. The Tg-modified oligodeoxynucleotide was annealed with either 5'-d(A(13)C(14)A(15)A(16)A(17)C(18)A(19)C(20)G(21)C(22)A(23)C(24))-3', forming the Tg(6) x A(19) base pair, corresponding to the oxidative damage of thymine in DNA, or 5'-d(A(13)C(14)A(15)A(16)A(17)C(18)G(19)C(20)G(21)C(22)A(23)C(24))-3', forming the mismatched Tg(6) x G(19) base pair, corresponding to the formation of Tg following oxidative damage and deamination of 5-methylcytosine in DNA. At 30 degrees C, the equilibrium ratio of cis-5R,6S:trans-5R,6R epimers was 7:3 for the duplex containing the Tg(6) x A (19) base pair. In contrast, for the duplex containing the Tg(6) x G(19) base pair, the cis-5R,6S:trans-5R,6R equilibrium favored the cis-5R,6S epimer; the level of the trans-5R,6R epimer remained below the level of detection by NMR. The data suggested that Tg disrupted hydrogen bonding interactions, either when placed opposite to A(19) or G(19). Thermodynamic measurements indicated a 13 degrees C reduction of T(m) regardless of whether Tg was placed opposite dG or dA in the complementary strand. Although both pairings increased the free energy of melting by 3 kcal/mol, the melting of the Tg x G pair was more enthalpically favored than was the melting of the Tg x A pair. The observation that the position of the equilibrium between the cis-5R,6S and trans-5R,6R thymine glycol epimers in duplex DNA was affected by the identity of the complementary base extends upon observations that this equilibrium modulates the base excision repair of Tg [Ocampo-Hafalla, M. T.; Altamirano, A.; Basu, A. K.; Chan, M. K.; Ocampo, J. E.; Cummings, A., Jr.; Boorstein, R. J.; Cunningham, R. P.; Teebor, G. W. DNA Repair (Amst) 2006, 5, 444-454].
authors.affiliation: Department of Chemistry, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235, USA.
authors.forename: Kyle L
authors.initials: KL
authors.lastname: Brown
authors.forename: Travis
authors.initials: T
authors.lastname: Adams
authors.forename: Vijay P
authors.initials: VP
authors.lastname: Jasti
authors.forename: Ashis K
authors.initials: AK
authors.lastname: Basu
authors.forename: Michael P
authors.initials: MP
authors.lastname: Stone
mesh_terms: D002236:Carbohydrate Conformation; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D003855:Deoxyribose / Q000737:chemistry / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry; D013816:Thermodynamics; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D009841:Oligonucleotides; C029389:thymine glycol; D003855:Deoxyribose; D004247:DNA; D013941:Thymine