(J. Am. Chem. Soc., 2011, 133, 4874–4881)
膜蛋白的动力学与温度、水和磷脂双分子层等环境因素密切相关。迄今为止，“蛋白质对环境因素的响应”的研究主要是停留在分子整体水平上，而在蛋白质残基位点水平上的研究非常少。在本文中，我们利用高分辨固体核磁共振(Solid-state NMR, SSNMR)在高场下研究了绿色视紫质膜蛋白(Proteorhodopsin, PR, 是一种光驱动的质子泵)的动力学，分别采用基于化学键传递或空间传递的固体核磁相关实验分析了运动性强或运动受限的蛋白质残基。结果表明：水分子极大地促进了蛋白质链端和螺旋间loop区的残基运动，而对跨膜螺旋或刚性loop区残基的运动影响较小。与之相反的是，磷脂膜发生由凝胶态向液晶态的转变后，它对链端或大部分loop区残基的运动性影响较小；而对螺旋C、F、G和EF loop区残基的运动性(10-6s)具有明显的增强——这些区域的动力学变化与PR参与的光循环功能相关。该研究对于理解PR的功能机制具有重要意义，同时也为人们在残基位点水平上研究水和磷脂对膜蛋白动力学的影响作出了重要探索。
Molecular Dynamics of Proteorhodopsin in Lipid Bilayers by Solid-State NMR
Abstract Environmental factors such as temperature, hydration, and lipid bilayer properties are tightly coupled to the dynamics of membrane proteins. So far, site-resolved data visualizing the protein’s response to alterations in these factors are rare, and conclusions had to be drawn from dynamic data averaged over the whole protein structure. In the current study, high-resolution solid-state NMR at high magnetic field was used to investigate their effects on themolecular dynamics of green proteorhodopsin, a bacterial light-driven proton pump. Through-space and through-bond correlation experiments were employed to identify and characterize highly mobile and motionally restricted regions of proteorhodopsin. Our data show that hydration water plays an essential role for enhancing molecular dynamics of residues in tails and interhelical loops, while it is found less important for residues in transmembrane domains or rigid, structured loop segments. In contrast, switching the lipids from the gel to their liquid crystalline phase enhances molecular fluctuations mainly in transmembrane helices on a time scale of 10-6 s, but has little effect on loop and tail residues. Increased mobility is especially observed in helices C, F, and G, but also in the EF loop. Fluctuations in those regions are relevant to structural dynamics during the photocycle ofproteorhodopsin. Our data are important for the functional understanding ofproteorhodopsin, but also offer an important contribution to the general understanding of site-resolved effects of water and lipid bilayers onto the dynamic properties of membrane proteins.