Force-induced melting of the DNA double helix. 2. Effect of solution conditions
Force-induced melting of the DNA double helix. 2. Effect of solution conditions
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DOI：
10.1016/s0006-3495(01)76068-7
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发表时间：
2001-02-01
影响因子：
3.4
通讯作者：
Bloomfield, VA
中科院分区：
文献类型：
--
作者：
Rouzina, I;Bloomfield, VA
在本文中，我们考虑了随附论文中提出的一般理论的含义，以解释涉及溶液温度、pH 值和离子强度等变量的 DNA 过度拉伸实验。我们在力-温度空间中找到了 DNA 螺旋-螺旋相界。在显着低于常规（零力）DNA 熔解温度的温度下，过度拉伸力 f(ov)(T) 预计将随温度几乎呈线性下降。我们计算了这种依赖性的斜率作为 DNA 熔化时熵和热容变化的函数。拟合实验 f(ov)(T) 依赖性可以确定这两个量与其量热值非常一致。在略高于常规 DNA 熔解温度的温度下，我们预测中等力会使双链 DNA 稳定，较高的力会使双链 DNA 不稳定。因此，DNA 拉伸曲线 f(b) 应表现出两次而不是一次过度拉伸转变：从单链 (ss) 到双链 (ds)，然后以更高的力返回。我们还预测，DNA 溶液条件的任何影响其熔解温度的变化都应该对 DNA 过度拉伸力产生类似的影响。该结果用于根据 DNA 熔解温度对 pH 的已知依赖性，计算 DNA 过度拉伸力对溶液 pH 的依赖性 f(ov)(pH)。计算出的 f(ov)(pH) 与其实验测定值非常吻合（M. C. Williams、J. R. Wenner、I. Rouzina 和 V. A. Bloomfield, Biophys. J.，已接受发表）。最后，我们定量地解释了交联和非交联 DNA 的 DNA 过度拉伸力对溶液离子强度的测量依赖性。与交联或双链过度拉伸的 S-DNA 相比，非交联 DNA 中 f(ov) 的盐依赖性更强，这是由于其在熔化状态下的线性电荷密度较低。
In this paper, we consider the implications of the general theory developed in the accompanying paper, to interpret experiments on DNA overstretching that involve variables such as solution temperature, pH, and ionic strength. We find the DNA helix-coil phase boundary in the force-temperature space. At temperatures significantly below the regular (zero force) DNA melting temperature, the overstretching force, f(ov)(T), is predicted to decrease nearly linearly with temperature. We calculate the slope of this dependence as a function of entropy and heat-capacity changes upon DNA melting. Fitting of the experimental f(ov)(T) dependence allows determination of both of these quantities in very good agreement with their calorimetric values. At temperatures slightly above the regular DNA melting temperature, we predict stabilization of dsDNA by moderate forces, and destabilization by higher forces. Thus the DNA stretching curves, f(b), should exhibit two rather than one overstretching transitions: from single stranded (ss) to double stranded (ds) and then back at the higher force. We also predict that any change in DNA solution conditions that affects its melting temperature should have a similar effect on DNA overstretching force. This result is used to calculate the dependence of DNA overstretching force on solution pH, f(ov)(pH), from the known dependence of DNA melting temperature on pH. The calculated f(ov)(pH) is in excellent agreement with its experimental determination (M. C. Williams, J. R. Wenner, I. Rouzina, and V. A. Bloomfield, Biophys. J., accepted for publication). Finally, we quantitatively explain the measured dependence of DNA overstretching force on solution ionic strength for crosslinked and noncrosslinked DNA. The much stronger salt dependence of f(ov) in noncrosslinked DNA results from its lower linear charge density in the melted state, compared to crosslinked or double-stranded overstretched S-DNA.