Molecular origin of time-dependent fluorescence shifts in proteins
Molecular origin of time-dependent fluorescence shifts in proteins
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DOI：
10.1073/pnas.0504181102
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发表时间：
2005-09-27
影响因子：
11.1
通讯作者：
Halle, B
中科院分区：
文献类型：
--
作者：
Nilsson, L;Halle, B
时间分辨荧光光谱越来越多地用于探测生物大分子和膜的水界面上的分子运动。通过记录荧光频率的时间变化，可以探测到发色团附近的热原子波动。从这种荧光斯托克斯位移（FSS）实验中，可以推断水化层中的水运动减慢了1-3个数量级。为了为FSS数据的解释提供更安全的基础，我们使用分子动力学模拟来检查蛋白质中色氨酸残基的FSS的分子起源。利用线性响应理论将FSS分解为水和蛋白质组分，发现水组分在静态FSS中占主导地位，但衰减迅速。因此，在几皮秒后，FSS基本上反映了蛋白质动力学，包括发色团的自我运动。由于其集体性质，FSS响应对单个水分子的运动不敏感。缓慢波动的蛋白质群引起的集体水位移在水自相关函数中引入了长时间尾，但这种动态耦合在观察到的FSS中几乎没有表现出来。我们的分析将FSS数据与高动态水化层的图像相一致，这主要来自磁弛豫色散和模拟研究，并要求对先前在生物分子和其他界面上的缓慢水化动力学方面对FSS衰减的解释进行修订。
Time-resolved fluorescence spectroscopy is used increasingly to probe molecular motions at the aqueous interfaces of biological macromolecules and membranes. By recording the time variation of the fluorescence frequency, thermal atomic fluctuations in the vicinity of the chromophore can be probed. From such fluorescence Stokes shift (FSS) experiments, it has been inferred that water motions in the hydration layer are slowed down by 1-3 orders of magnitude. To provide a more secure foundation for the interpretation of FSS data, we use molecular dynamics simulations to examine the molecular origin of the FSS from a tryptophan residue in a protein. By using linear response theory to decompose the FSS into its water and protein components, we find that the water component dominates the static FSS but decays rapidly. Thus, after a few picoseconds, the FSS essentially reflects protein dynamics, including the self-motion of the chromophore. Because of its collective nature, the FSS response is insensitive to the motion of individual water molecules. Collective water displacement by slowly fluctuating protein groups introduces a long-time-tail in the water autocorrelation function, but this dynamic coupling is hardly manifested in the observed FSS. Our analysis reconciles FSS data with the picture of a highly dynamic hydration layer, derived mainly from magnetic relaxation dispersion and simulation studies, and calls for a revision of previous interpretations of FSS decays in terms of slow hydration dynamics at biomolecular and other interfaces.