Gelfand C A, Plum G E, Grollman A P, Johnson F, Breslauer K J
Department of Chemistry, Rutgers, The State University of New Jersey, Piscataway 58854-8087, USA.
Biochemistry. 1998 Sep 8;37(36):12507-12. doi: 10.1021/bi981090b.
The exocyclic base adduct 3,N4-deoxyethenocytosine (epsilonC) is a common DNA lesion that can arise from carcinogen exposure and/or as a biproduct of cellular processes. We have examined the thermal and thermodynamic impact of this lesion on DNA duplex properties, as well as the structural alterations imparted by the lesion. For these studies, we used calorimetric and spectroscopic techniques to investigate a family of 13-mer DNA duplexes of the form (5'CGCATGNGTACGC3')x(3'GCGTACNCATGCG5'), where the central NxN base pair represents the four standard Watson-Crick base pairs (corresponding to four control duplexes), and where either one of the N bases has been replaced by epsilonC, yielding eight test duplexes. Studies on these 12 duplexes permit us to assess the impact of the epsilonC lesion as a function of sequence context. Our spectroscopic and calorimetric data allow us to reach the following conclusions: (i) The epsilonC lesion imparts a large penalty on duplex stability, with sequence context only modestly modulating the extent of this lesion-induced destabilization. This result contrasts with our recent studies of duplexes with abasic sites, where sequence context was found to be the predominant determinant of thermodynamic damage. (ii) For the epsilonC-containing duplexes, sequence context effects are most often observed in the enthalpic contribution to lesion-induced duplex destabilization. However, due to compensating entropies, the free energy changes associated with this lesion-induced duplex destablization are nearly independent of sequence context. (iii) Despite significant lesion-induced changes in duplex energetics, our spectroscopic probes detect only modest lesion-induced changes in duplex structure. In fact, the overall duplex maintains a global B-form conformation, in agreement with NMR structural data. We discuss possible interpretations of the apparent disparity between the severe thermodynamic and relatively mild structural impacts of the epsilonC lesion on duplex properties. We also note and discuss the implications of empirical correlations between biophysical and biological properties of lesion-containing duplexes.
环外碱基加合物3,N4-脱氧乙烯基胞嘧啶（εC）是一种常见的DNA损伤，可由致癌物暴露和/或作为细胞过程的副产物产生。我们研究了这种损伤对DNA双链体性质的热学和热力学影响，以及该损伤引起的结构改变。对于这些研究，我们使用量热和光谱技术来研究一系列形式为(5'CGCATGNGTACGC3')x(3'GCGTACNCATGCG5')的13聚体DNA双链体，其中中央的NxN碱基对代表四个标准的沃森-克里克碱基对（对应于四个对照双链体），并且其中一个N碱基被εC取代，产生八个测试双链体。对这12个双链体的研究使我们能够评估εC损伤作为序列背景函数的影响。我们的光谱和量热数据使我们能够得出以下结论：（i）εC损伤对双链体稳定性造成很大损失，序列背景仅适度调节这种损伤诱导的去稳定化程度。这一结果与我们最近对含有无碱基位点的双链体的研究形成对比，在该研究中发现序列背景是热力学损伤的主要决定因素。（ii）对于含εC的双链体，序列背景效应最常出现在损伤诱导的双链体去稳定化的焓贡献中。然而，由于补偿熵，与这种损伤诱导的双链体去稳定化相关的自由能变化几乎与序列背景无关。（iii）尽管损伤引起双链体能量学有显著变化，但我们的光谱探针仅检测到损伤引起的双链体结构有适度变化。事实上，整体双链体保持全局B型构象，这与NMR结构数据一致。我们讨论了εC损伤对双链体性质的严重热力学影响和相对温和的结构影响之间明显差异的可能解释。我们还注意并讨论了含损伤双链体的生物物理和生物学性质之间经验相关性的含义。
