The Impact of an Exocyclic Cytosine Adduct on DNA Duplex Properties: Significant Thermodynamic Consequences Despite Modest Lesion-Induced Structural Alterations

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• 作者：Craig A. Gelfand ; G. Eric Plum ; Arthur P. Grollman ; Francis Johnson ; and Kenneth J. Breslauer
• 刊名：Biochemistry
• 出版年：1998
• 出版时间：September 8, 1998
• 年：1998
• 卷：37
• 期：36
• 页码：12507 - 12512
• 全文大小：104K
• 年卷期：v.37,no.36(September 8, 1998)
• ISSN：1520-4995

文摘

The exocyclic base adduct 3,N⁴-deoxyethenocytosine (C) is a common DNA lesion that canarise from carcinogen exposure and/or as a biproduct of cellular processes. We have examined the thermaland thermodynamic impact of this lesion on DNA duplex properties, as well as the structural alterationsimparted by the lesion. For these studies, we used calorimetric and spectroscopic techniques to investigatea family of 13-mer DNA duplexes of the form (^5'CGCATGNGTACGC^3')(^3'GCGTACNCATGCG^5'), wherethe central NN base pair represents the four standard Watson-Crick base pairs (corresponding to fourcontrol duplexes), and where either one of the N bases has been replaced by C, yielding eight test duplexes.Studies on these 12 duplexes permit us to assess the impact of the C lesion as a function of sequencecontext. Our spectroscopic and calorimetric data allow us to reach the following conclusions: (i) The Clesion imparts a large penalty on duplex stability, with sequence context only modestly modulating theextent of this lesion-induced destabilization. This result contrasts with our recent studies of duplexeswith abasic sites, where sequence context was found to be the predominant determinant of thermodynamicdamage. (ii) For the C-containing duplexes, sequence context effects are most often observed in theenthalpic contribution to lesion-induced duplex destabilization. However, due to compensating entropies,the free energy changes associated with this lesion-induced duplex destablization are nearly independentof sequence context. (iii) Despite significant lesion-induced changes in duplex energetics, our spectroscopicprobes detect only modest lesion-induced changes in duplex structure. In fact, the overall duplex maintainsa global B-form conformation, in agreement with NMR structural data. We discuss possible interpretationsof the apparent disparity between the severe thermodynamic and relatively mild structural impacts of theC lesion on duplex properties. We also note and discuss the implications of empirical correlations betweenbiophysical and biological properties of lesion-containing duplexes.