Plum G E, Grollman A P, Johnson F, Breslauer K J
Department of Chemistry, Rutgers, State University of New Jersey, New Brunswick 08903, USA.
Biochemistry. 1995 Dec 12;34(49):16148-60. doi: 10.1021/bi00049a030.
As part of an overall program to characterize the impact of mutagenic lesions on the physiochemical properties of DNA, we report here the results of a comparative spectroscopic and calorimetric study on a family of DNA duplexes both with and without the oxidative lesion 2'-deoxy-7-hydro-8-oxoguanosine (8-oxodG). Specifically, we have studied a family of eight 13-mer duplexes of the form [5'-GCGTAC[G* or G]CATGCG-3'].[3'-CGCATG[C, A, T, or G]GTACGC-5'] in which G* is the 8-oxodG lesion. These eight duplexes, which we designate by the identity of the variable central base pair (e.g., GC), reflect two subsets: four duplexes in which the modified guanine base is positioned opposite each of the four possible canonical residues (GC, GA, GG, GT) and the corresponding four "control" duplexes in which the guanine is not modified (GC, GA, GG, GT). The data derived from our spectroscopic and calorimetric measurements on these eight duplexes allow us to evaluate the influence of the 8-oxodG lesion, as well as the base opposite the lesion, on the conformation, the thermal and thermodynamic stability, and the melting thermodynamics of the host DNA duplex. We find that modification of dG to 8-oxodG (G) does not change the global DNA duplex conformation as judged by circular dichroism spectra. Despite this structural similarity, our data reveal that the dG to dG* modification does influence duplex thermal and thermodynamic properties, some of which depend on the base opposite the lesion. Thus, apparent structural identity does not mean that two duplexes necessarily will exhibit equivalent thermal and/or thermodynamic properties. In general, we find that the thermodynamic effects induced by the lesion (e.g., GC vs G*C) or by mismatched base pairs (e.g., GC vs GG) can result in relatively large changes in enthalpy which are partially or wholly compensated entropically to produce relatively modest changes in free energy. Our data also suggest that the biologically observed differential recognition of 8-oxodG duplexes and the preferential nucleotide insertion opposite 8-oxodG residues cannot be rationalized simply in terms of large thermodynamic differences.
作为表征诱变损伤对DNA物理化学性质影响的整体计划的一部分，我们在此报告了一项对一系列含有和不含有氧化损伤2'-脱氧-7-氢-8-氧代鸟苷（8-氧代dG）的DNA双链体进行的光谱和量热比较研究的结果。具体而言，我们研究了一组八个13聚体双链体，其形式为[5'-GCGTAC[G* 或 G]CATGCG-3']·[3'-CGCATG[C、A、T或G]GTACGC-5']，其中G* 是8-氧代dG损伤。这八个双链体，我们根据可变中心碱基对的身份来命名（例如，GC），反映了两个子集：四个双链体中，修饰的鸟嘌呤碱基与四种可能的标准残基中的每一个相对（GC、GA、GG、GT），以及相应的四个“对照”双链体，其中鸟嘌呤未被修饰（GC、GA、GG、GT）。从我们对这八个双链体的光谱和量热测量中获得的数据，使我们能够评估8-氧代dG损伤以及损伤对面的碱基对宿主DNA双链体的构象、热稳定性和热力学稳定性以及解链热力学的影响。我们发现，通过圆二色光谱判断，将dG修饰为8-氧代dG（G）不会改变整体DNA双链体构象。尽管存在这种结构相似性，但我们的数据表明，从dG到dG* 的修饰确实会影响双链体的热性质和热力学性质，其中一些性质取决于损伤对面的碱基。因此，明显的结构一致性并不意味着两个双链体必然会表现出等效的热性质和/或热力学性质。一般来说，我们发现损伤（例如，GC与G*C）或错配碱基对（例如，GC与GG）引起的热力学效应会导致焓的相对较大变化，这些变化会部分或全部被熵补偿，从而在自由能中产生相对较小的变化。我们的数据还表明，生物学上观察到的对8-氧代dG双链体的差异识别以及在8-氧代dG残基对面优先插入核苷酸，不能简单地根据大的热力学差异来解释。
