Selective localization and rotational immobilization of univalent cations on quadruplex DNA.
Selective localization and rotational immobilization of univalent cations on quadruplex DNA.
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DOI：
10.1021/bi00211a023
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发表时间：
1993-12
期刊：
影响因子：
2.9
通讯作者：
Q. Xu;H. Deng;W. Braunlin
中科院分区：
文献类型：
--
作者：
Q. Xu;H. Deng;W. Braunlin
低聚物d（T2G4T）的四链体结构在K+存在下比在Na+存在下更稳定。这种增强的稳定性与K+优先结合到四链体上的少量特定位点相关。相比之下，Na+和K+在平等的基础上竞争大气结合。39 K+和23 Na+，当具体结合，显着抑制其旋转流动性，使四极松弛反映的低聚物，这发生在纳秒的时间尺度上的分子翻滚。这种旋转固定与大气中结合阳离子的高旋转流动性形成鲜明对比。另一方面，溶液中所有NMR可见的39K+在所有环境（自由的、特异性结合的和大气结合的）之间快速交换，这意味着特异性配位的39K+的寿命必须显著短于毫秒。类似的结论也适用于23 Na+。寡聚体d（T2G4T）在NaCl溶液中形成两个不同的Hoogsteen碱基配对结构，由一个大的动力学屏障隔开。这两种结构都不像KCl溶液中形成的四链体结构那样稳定。这两种结构中只有一种与结合的23 Na+的旋转固定有关。
The quadruplex structure of the oligomer d(T2G4T) is more stable in the presence of K+ than in the presence of Na+. This enhanced stability correlates with the preferential binding of K+ to a small number of specific sites on the quadruplex. In contrast, Na+ and K+ compete on an equal footing for atmospheric binding. Both 39K+ and 23Na+ are, when specifically bound, significantly inhibited in their rotational mobility, so that the quadrupolar relaxation reflects the molecular tumbling of the oligomer, which occurs on the time scale of nanoseconds. This rotational immobilization is in distinct contrast to the high rotational mobility of atmospherically bound cations. On the other hand, all NMR-visible 39K+ in solution is in rapid exchange among all environments (free, specifically bound, and atmospherically bound) implying that the lifetime of specifically coordinated 39K+ must be significantly shorter than a millisecond. A similar conclusion holds for 23Na+. The oligomer d(T2G4T) forms two distinct Hoogsteen base-paired structures in NaCl solution, separated by a large kinetic barrier. Neither of these structures is as stable with respect to base pair opening as is the quadruplex structure formed in KCl solution. Only one of these two structures is associated with rotational immobilization of bound 23Na+.