Department of Physics, Tampere University of Technology, Finland VTT Technical Research Center of Finland, Espoo, Finland.
Faraday Discuss. 2010;144:411-30; discussion 445-81. doi: 10.1039/b901487j.
Currently, there is no comprehensive model for the dynamics of cellular membranes. The understanding of even the basic dynamic processes, such as lateral diffusion of lipids, is still quite limited. Recent studies of one-component membrane systems have shown that instead of single-particle motions, the lateral diffusion is driven by a more complex, concerted mechanism for lipid diffusion (E. Falck et al., J. Am. Chem. Soc., 2008, 130, 44-45), where a lipid and its neighbors move in unison in terms of loosely defined clusters. In this work, we extend the previous study by considering the concerted lipid diffusion phenomena in many-component raft-like membranes. This nature of diffusion phenomena emerge in all the cases we have considered, including both atom-scale simulations of lateral diffusion within rafts and coarse-grained MARTINI simulations of diffusion in membranes characterized by coexistence of raft and non-raft domains. The data allows us to identify characteristic time scales for the concerted lipid motions, which turn out to range from hundreds of nanoseconds to several microseconds. Further, we characterize typical length scales associated with the correlated lipid diffusion patterns and find them to be about 10 nm, or even larger if weak correlations are taken into account. Finally, the concerted nature of lipid motions is also found in dissipative particle dynamics simulations of lipid membranes, clarifying the role of hydrodynamics (local momentum conservation) in membrane diffusion phenomena.
目前，还没有关于细胞膜动力学的综合模型。即使是对基本的动态过程（如脂质的侧向扩散）的理解也非常有限。最近对单一组分膜系统的研究表明，脂质的侧向扩散不是由单个粒子的运动驱动的，而是由一种更复杂的协同机制驱动的，这种协同机制是为了脂质扩散（E. Falck 等人，J. Am. Chem. Soc.，2008，130，44-45），其中脂质及其相邻分子以松散定义的簇的形式协同运动。在这项工作中，我们通过考虑多组分筏状膜中的协同脂质扩散现象来扩展之前的研究。在我们考虑的所有情况下都会出现这种扩散现象，包括筏内侧向扩散的原子尺度模拟和具有筏和非筏域共存的膜中扩散的粗粒化 MARTINI 模拟。这些数据使我们能够确定协同脂质运动的特征时间尺度，结果表明这些时间尺度范围从数百纳秒到数微秒。此外，我们还对与相关脂质扩散模式相关的典型长度尺度进行了特征化，并发现它们约为 10nm，如果考虑到较弱的相关性，其长度甚至会更大。最后，在脂质膜的耗散粒子动力学模拟中也发现了脂质运动的协同性质，这阐明了流体动力学（局部动量守恒）在膜扩散现象中的作用。
