Solution Structure of the N-(Deoxyguanosin-8-yl)-1-aminopyrene ([AP]dG) Adduct Opposite dA in a DNA Duplex

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• 作者：Zhengtian Gu ; Andrey Gorin ; Ramji Krishnasamy ; Brian E. Hingerty ; Ashis K. Basu ; Suse Broyde ; and Dinshaw J. Patel
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：August 17, 1999
• 年：1999
• 卷：38
• 期：33
• 页码：10843 - 10854
• 全文大小：220K
• 年卷期：v.38,no.33(August 17, 1999)
• ISSN：1520-4995

文摘

Solution structural studies have been undertaken on the aminopyrene-C⁸-dG ([AP]dG) adductin the d(C5-[AP]G6-C7)·d(G16-A17-G18) sequence context in an 11-mer duplex with dA opposite[AP]dG, using proton-proton distance and intensity restraints derived from NMR data in combinationwith distance-restrained molecular mechanics and intensity-restrained relaxation matrix refinementcalculations. The exchangeable and nonexchangeable protons of the aminopyrene and the nucleic acidwere assigned following analysis of two-dimensional NMR data sets on the [AP]dG·dA 11-mer duplexin H₂O and D₂O solution. The broadening of several resonances within the d(G16-A17-G18) segmentpositioned opposite the [AP]dG6 lesion site resulted in weaker NOEs, involving these protons in theadduct duplex. Both proton and carbon NMR data are consistent with a syn glycosidic torsion angle forthe [AP]dG6 residue in the adduct duplex. The aminopyrene ring of [AP]dG6 is intercalated into theDNA helix between intact Watson-Crick dC5·dG18 and dC7·dG16 base pairs and is in contact withdC5, dC7, dG16, dA17, and dG18 residues that form a hydrophobic pocket around it. The intercalatedAP ring of [AP]dG6 stacks over the purine ring of dG16 and, to a lesser extent dG18, while the loopedout deoxyguanosine ring of [AP]dG6 stacks over dC5 in the solution structure of the adduct duplex. ThedA17 base opposite the adduct site is not looped out of the helix but rather participates in an in-planeplatform with adjacent dG18 in some of the refined structures of the adduct duplex. The solution structuresare quite different for the [AP]dG·dA 11-mer duplex containing the larger aminopyrene ring (reported inthis study) relative to the previously published [AF]dG·dA 11-mer duplex containing the smalleraminofluorene ring (Norman et al., Biochemistry 28, 7462-7476, 1989) in the same sequence context.Both the modified syn guanine and the dA positioned opposite it are stacked into the helix with theaminofluorene chromophore displaced into the minor groove in the latter adduct duplex. By contrast, theaminopyrenyl ring participates in an intercalated base-displaced structure in the present study of the [AP]dG·dA 11-mer duplex and in a previously published study of the [AP]dG·dC 11-mer duplex (Mao et al.,Biochemistry 35, 12659-12670, 1996). Such intercalated base-displaced structures without hydrogenbonding between the [AP]dG adduct and dC or mismatched dA residues positioned opposite it, if presentat a replication fork, may cause polymerase stalling and formation of a slipped intermediate that couldproduce frameshift mutations, the most dominant mutagenic consequence of the [AP]dG lesion.