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Publication Abstract from PubMed

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'-dA ((2S)-N6-HB-dA) adducts ( Tretyakova , N. , Lin , Y. , Sangaiah , R. , Upton , P. B. , and Swenberg , J. A. ( 1997 ) Carcinogenesis 18 , 137 - 147 ). The structure of the (2S)-N6-HB-dA adduct has been determined in the 5'-d(C1G2G3A4C5Y6A7G8A9A10G11)-3':5'-d(C12T13T14C15T16T17G18T19 C20C21G22)-3' 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' direction. At the Calpha carbon, the methylene protons of the modified nucleobase Y6 faced the 5' direction, which placed the Cbeta carbon in the 3' direction. The Cbeta hydroxyl group faced toward the solvent, as did carbons Cgamma and Cdelta. The Cbeta 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-Crick 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' neighbor C5, but it did with its 3' neighbor A7. The complementary thymine T17 stacked well with both 5' and 3' neighbors T16 and G18. The presence of the (2S)-N6-HB-dA resulted in a 5 degrees C reduction in the Tm of the duplex, which is attributed to less favorable stacking interactions and adduct accommodation in the major groove.

Major Groove Orientation of the (2S)-N-(2-Hydroxy-3-buten-1-yl)-2'-deoxyadenosine DNA Adduct Induced by 1,2-Epoxy-3-butene.,Kowal EA, Wickramaratne S, Kotapati S, Turo M, Tretyakova N, Stone MP Chem Res Toxicol. 2014 Sep 19. PMID:25238403^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.