Major Groove Orientation of the (2S)-N6-(2-Hydroxy-3-buten-1-yl)-2鈥?deoxyadenosine DNA Adduct Induced by 1,2-Epoxy-3-butene

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• 作者：Ewa A. Kowal ; Susith Wickramaratne ; Srikanth Kotapati ; Michael Turo ; Natalia Tretyakova ; Michael P. Stone
• 刊名：Chemical Research in Toxicology
• 出版年：2014
• 出版时间：October 20, 2014
• 年：2014
• 卷：27
• 期：10
• 页码：1675-1686
• 全文大小：578K
• ISSN：1520-5010

文摘

1,3-Butadiene (BD) is an environmental and occupational toxicant classified as a human carcinogen. It is oxidized by cytochrome P450 monooxygenases to 1,2-epoxy-3-butene (EB), which alkylates DNA. BD exposures lead to large numbers of mutations at A:T base pairs even though alkylation of guanines is more prevalent, suggesting that one or more adenine adducts of BD play a role in BD-mediated genotoxicity. However, the etiology of BD-mediated genotoxicity at adenine remains poorly understood. EB alkylates the N⁶ exocyclic nitrogen of adenine to form N⁶-(hydroxy-3-buten-1-yl)-2鈥?dA ((2S)-N⁶-HB-dA) adducts (Tretyakova, N., Lin, Y., Sangaiah, R., Upton, P. B., and Swenberg, J. A. (1997) Carcinogenesis18, 137鈭?47). The structure of the (2S)-N⁶-HB-dA adduct has been determined in the 5鈥?d(C¹G²G³A⁴C⁵Y⁶A⁷G⁸A⁹A¹⁰G¹¹)-3鈥?5鈥?d(C¹²T¹³T¹⁴C¹⁵T¹⁶T¹⁷G¹⁸T¹⁹ C²⁰C²¹G²²)-3鈥?duplex [Y = (2S)-N⁶-HB-dA] containing codon 61 (underlined) of the human N-ras protooncogene, from NMR spectroscopy. The (2S)-N⁶-HB-dA adduct was positioned in the major groove, such that the butadiene moiety was oriented in the 3鈥?direction. At the C_伪 carbon, the methylene protons of the modified nucleobase Y⁶ faced the 5鈥?direction, which placed the C_尾 carbon in the 3鈥?direction. The C_尾 hydroxyl group faced toward the solvent, as did carbons C_纬 and C_未. The C_尾 hydroxyl group did not form hydrogen bonds with either T¹⁶ O⁴ or T¹⁷ O⁴. The (2S)-N⁶-HB-dA nucleoside maintained the anti conformation about the glycosyl bond, and the modified base retained Watson鈥揅rick base pairing with the complementary base (T¹⁷). The adduct perturbed stacking interactions at base pairs C⁵:G¹⁸, Y⁶:T¹⁷, and A⁷:T¹⁶ such that the Y⁶ base did not stack with its 5鈥?neighbor C⁵, but it did with its 3鈥?neighbor A⁷. The complementary thymine T¹⁷ stacked well with both 5鈥?and 3鈥?neighbors T¹⁶ and G¹⁸. The presence of the (2S)-N⁶-HB-dA resulted in a 5 掳C reduction in the T_m of the duplex, which is attributed to less favorable stacking interactions and adduct accommodation in the major groove.