Jin R, Gaffney B L, Wang C, Jones R A, Breslauer K J
Department of Chemistry, Rutgers, State University of New Jersey, Piscataway 08855.
Proc Natl Acad Sci U S A. 1992 Sep 15;89(18):8832-6. doi: 10.1073/pnas.89.18.8832.
We report a combined thermodynamic and structural characterization of a DNA tetraplex. Using spectroscopic and calorimetric techniques, we demonstrate that d(TG3T) and d(TG3T2G3T), in the presence of K+, form stable tetramolecular complexes. From differential scanning calorimetry measurements, we obtain the following thermodynamic profiles for formation of each tetraplex at 25 degrees C: delta G degrees = -6.9 kcal/mol of tetraplex (or -2.3 kcal/mol of tetrad; 1 cal = 4.184 J), delta H degrees = -62.6 kcal/mol of tetraplex (or -20.9 kcal/mol of tetrad), and delta S degrees = -186.9 cal.K-1.mol-1 of tetraplex (or -62.3 cal.K-1.mol-1 of tetrad) for the d(TG3T) tetraplex; and delta G degrees = -20.2 kcal/mol of tetraplex (or -3.4 kcal/mol of tetrad), delta H degrees = -123.2 kcal/mol of tetraplex (or -20.5 kcal/mol of tetrad), and delta S degrees = -346.0 cal.K-1.mol-1 of tetraplex (or -57.7 cal.K-1.mol-1 of tetrad) for the d(TG3T2G3T) tetraplex. These data demonstrate that at 25 degrees C a G-tetrad can exhibit considerable stability, comparable to or even exceeding that of most Watson-Crick nearest-neighbor interactions, with this stability resulting from a very favorable enthalpy of formation. Temperature-dependent CD measurements reveal that the melting temperatures of both tetraplexes exhibit unusually low salt dependences. This unexpected behavior may reflect a diminished charge density due to bound K+ ions. For each complex, the Na+ and K+ forms exhibit drastically different isothermal and temperature-dependent CD profiles, with the K+ forms of each tetraplex melting more sharply and at a higher temperature than the Na+ forms. Using one- and two-dimensional NMR techniques, we show that the strands in the tetramolecular complex of d(TG3T), K+ are all parallel and that the guanine glycosidic conformations are all anti.
我们报告了一种DNA四链体的热力学和结构联合表征。使用光谱和量热技术，我们证明在K⁺存在下，d(TG3T)和d(TG3T2G3T)形成稳定的四分子复合物。通过差示扫描量热法测量，我们获得了在25℃下每种四链体形成的以下热力学曲线：对于d(TG3T)四链体，ΔG° = -6.9千卡/摩尔四链体（或-2.3千卡/摩尔四分体；1卡 = 4.184焦耳），ΔH° = -62.6千卡/摩尔四链体（或-20.9千卡/摩尔四分体），以及ΔS° = -186.9卡·K⁻¹·摩尔⁻¹四链体（或-62.3卡·K⁻¹·摩尔⁻¹四分体）；对于d(TG3T2G3T)四链体，ΔG° = -20.2千卡/摩尔四链体（或-3.4千卡/摩尔四分体），ΔH° = -123.2千卡/摩尔四链体（或-20.5千卡/摩尔四分体），以及ΔS° = -346.0卡·K⁻¹·摩尔⁻¹四链体（或-57.7卡·K⁻¹·摩尔⁻¹四分体）。这些数据表明，在25℃时，一个鸟嘌呤四联体可以表现出相当高的稳定性，与大多数沃森-克里克最近邻相互作用相当甚至超过，这种稳定性源于非常有利的形成焓。温度依赖性圆二色性测量表明，两种四链体的熔解温度表现出异常低的盐依赖性。这种意外行为可能反映了由于结合的K⁺离子导致的电荷密度降低。对于每种复合物，Na⁺和K⁺形式表现出截然不同的等温及温度依赖性圆二色性曲线，每种四链体的K⁺形式比Na⁺形式更急剧地熔解且在更高温度下熔解。使用一维和二维核磁共振技术，我们表明d(TG3T)、K⁺的四分子复合物中的链都是平行的，并且鸟嘌呤糖苷构象都是反式的。
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