Cross-relaxation between macromolecular and solvent spins: The role of long-range dipole couplings
Cross-relaxation between macromolecular and solvent spins: The role of long-range dipole couplings
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DOI：
10.1063/1.1625632
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发表时间：
2003-12-15
影响因子：
4.4
通讯作者：
Halle, B
中科院分区：
文献类型：
--
作者：
Halle, B
核自旋弛豫分子间的偶极-偶极相互作用之间的大分子和溶剂核的时刻形成了广泛使用的方法研究大分子溶剂化的基础。特别是，蛋白质和水质子之间的分子间交叉弛豫[或核Overhauser效应（NOE）]已被用于探测与蛋白质表面相互作用的水分子的流动性。该方法基于分子间NOE范围较短（4 - 5 A）的假设，因此提供了有关监测蛋白质质子附近水合位点中单个水分子迁移率的信息。在这里，我们提出了一个理论分析的谱密度函数（SDF），管理在实验室固定和旋转帧的交叉松弛率。与用于结构测定的分子内NOE的r（-6）依赖性相反，分子间NOE显示为长程的，具有来自数千个水分子的重要贡献。为了对这种NOE进行一致的解释，有必要使用一种模型，该模型明确纳入了运动延迟的水合水分子以及未受干扰的散装水分子。我们制定了一个非均匀的溶剂迁移率的扩散模型，并解决它，以获得一个解析表达式的SDF。这种非均匀扩散模型的计算表明，与表面质子的分子间NOE占主导地位的远程偶极耦合散装水，因此提供很少或没有信息的水合动力学。这种意想不到的现象的物理基础是，弛豫引起的波动的特征时间尺度是更长的远程水分子，尽管他们更高的流动性。这里提出的分析结果一般适用于分子间偶极弛豫的类似或不类似（核或电子）自旋在各种实验情况下。(C)2003年，美国物理学会。
Nuclear spin relaxation by intermolecular dipole-dipole interactions between macromolecular and solvent nuclear moments forms the basis of a widely used method for investigating macromolecular solvation. In particular, intermolecular cross-relaxation [or nuclear Overhauser effect (NOE)] between protein and water protons has been used to probe the mobility of water molecules interacting with the protein surface. The method rests on the assumption that the intermolecular NOE is of short (4-5 A) range and thus provides information about the mobility of individual water molecules in hydration sites near the monitored protein protons. Here, we present a theoretical analysis of the spectral density function (SDF) that governs the cross-relaxation rates in the laboratory-fixed and rotating frames. In contrast to the r(-6) dependence of the intramolecular NOEs used for structure determination, the intermolecular NOE is shown to be long-ranged with important contributions from thousands of water molecules. For a consistent interpretation of such NOEs, it is necessary to use a model that explictly incorporates motionally retarded hydration water molecules as well as unperturbed bulk water molecules. We formulate a diffusion model with a nonuniform solvent mobility and solve it to obtain an analytical expression for the SDF. Calculations with this nonuniform diffusion model demonstrate that intermolecular NOEs with surface protons are dominated by long-range dipole couplings to bulk water and therefore provide little or no information about hydration dynamics. The physical basis of this unexpected phenomenon is that the characteristic time scale for relaxation-inducing fluctuations is longer for the more numerous remote water molecules, despite their higher mobility. The analytical results presented here are generally applicable to intermolecular dipolar relaxation of like or unlike (nuclear or electron) spins in a variety of experimental situations. (C) 2003 American Institute of Physics.