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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Studies on the structure and dynamics of the human telomeric G quadruplex by single-molecule fluorescence resonance energy transfer
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Studies on the structure and dynamics of the human telomeric G quadruplex by single-molecule fluorescence resonance energy transfer

机译：单分子荧光共振能量转移研究人端粒G四链体的结构和动力学

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摘要

We have investigated the structure and unfolding kinetics of the human telomeric intramolecular G quadruplex by using single-molecule fluorescence resonance energy transfer. An exploration of conformational heterogeneity revealed two stable folded conformations, in both sodium- and potassium-containing buffers, with small differences between their enthalpies and entropies. Both folded conformations can be opened by the addition of a 21-base complementary DNA oligonucleotide. The unfolding of both substates occurs at the same rate, which showed dependence on the monovalent metal cation present. Temperature-dependence studies in 100 mM KCl gave an apparent activation enthalpy and entropy of 6.4 +- 0.4 kcal·mol~(-1) and -52.3 +- 1.4 cal·mol~(-1)·K~(-1), respectively, indicating that the unfolding is entropically driven and can occur easily. In contrast, in 100 mM NaCl the respective values are 14.9 +- 0.2 kcal·mol~(-1) and -23.0 +- 0.8 cal·mol~(-1)·K~(-1), suggesting a more significant enthalpic barrier. Molecular modeling suggests that the two species are likely to be the parallel and antiparallel quadruplex structures. The unfolding free energy barrier is estimated to be between 3 and 15 k_BT based on Kramers' theory. We conclude that under near-physiological conditions these structures coexist and can interconvert on a minute time scale.
机译：我们已经研究了通过使用单分子荧光共振能量转移的人类端粒分子内G四链体的结构和展开动力学。对构象异质性的探索揭示了在含钠和钾的缓冲液中两个稳定的折叠构象，其焓和熵之间的差异很小。可以通过添加21个碱基的互补DNA寡核苷酸来打开两个折叠的构象。两个亚状态的展开以相同的速率发生，这表明对存在的单价金属阳离子有依赖性。在100 mM KCl中的温度依赖性研究显示表观活化焓和熵分别为6.4 +-0.4 kcal·mol〜（-1）和-52.3 +-1.4 cal·mol〜（-1）·K〜（-1），分别表示展开是受熵驱动的，并且很容易发生。相反，在100 mM NaCl中，各自的值为14.9 +-0.2 kcal·mol〜（-1）和-23.0 +-0.8 cal·mol〜（-1）·K〜（-1），表明焓更高屏障。分子建模表明这两个物种可能是平行和反平行四链体结构。根据克莱默斯理论，展开的自由能垒估计为3至15 k_BT。我们得出结论，在近乎生理的条件下，这些结构共存并可以在微小的时间尺度上相互转换。

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