Lateral diffusion of molecules in two-component lipid bilayer: a Monte Carlo simulation study.
Lateral diffusion of molecules in two-component lipid bilayer: a Monte Carlo simulation study.
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双组分脂质双层中分子的横向扩散：蒙特卡罗模拟研究。
DOI：
10.1021/jp045669x
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Biltonen,RodneyL
中科院分区：
文献类型：
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作者：
Sugar,IstvanP;Biltonen,RodneyL
膜成分的侧向扩散使得任何平面内膜反应成为可能，并在细胞膜信号传导中发挥关键作用。在这份报告中的平衡横向扩散的内在分子在等摩尔的DMPC/DSPC混合物模拟使用一个经过彻底测试的双态模型的双组分磷脂双层。该模型已经成功地计算了过量热容函数、DSPC簇之间最常见的中心到中心距离以及凝胶簇的分形维数（Sugar，I. P.，汤普森，T。E、比尔托宁河L.Biophys. J.1999，76，2099 - 2110）。在凝胶/流体混合相区域中，扩散的本征分子可以随时从流体到凝胶（或从凝胶到流体）改变其状态。本征分子扩散的一个共同特征是由模拟的平均首次通过时间曲线给出。我们发现，这些曲线可以描述为幂函数包含两个参数，α和β，除了附近的凝胶/流体或组成集群的逾渗阈值。我们还发现，内在分子参与近似正常的扩散，即，在极端的凝胶和流体相区，β_2的扩散是不规则的，而在凝胶/流体和凝胶/凝胶混合相区，β 2。在混合相区，当扩散分子的初始局域态不确定时，各组分均参与亚扩散（β > 2）。在凝胶/流体混合相区，最初位于流体团簇内部的分子参与亚扩散，而最初位于凝胶团簇内部的DMPC分子参与超扩散（β < 2）。膜中异常扩散的可能性显然是因为扩散分子访问各种不同的环境，其特征在于其相对接近各种膜组分。当双层膜的组分非随机分布时，扩散实际上是反常的。与随机分布的偏差与β密切相关。类似的NMR实验的结果，计算出的相对扩散系数连续下降，在凝胶/流体混合相区随着温度的降低。在明显的矛盾，通过光漂白（FRAP）后的荧光恢复测量的扩散表明存在一个阈值温度，低于该温度FRAP探针分子的长程扩散基本上被阻止。该阈值温度与凝胶簇的逾渗温度高度相关。
Lateral diffusion of membrane components makes possible any in-plane membrane reaction and has a key role in signaling in cell membranes. In this report the equilibrium lateral diffusion of intrinsic molecules in an equimolar DMPC/DSPC mixture is simulated using a thoroughly tested two-state model of two-component phospholipid bilayers. The model has been successful in calculating the excess heat capacity function, the most frequent center-to-center distances between DSPC clusters, and the fractal dimensions of gel clusters (Sugar, I. P., Thompson, T. E., Biltonen, R. L.Biophys. J.1999,76, 2099−2110). In the gel/fluid mixed phase region, a diffusing intrinsic molecule may change its state from fluid to gel (or from gel to fluid) at any time. A common characterization of the diffusion of intrinsic molecules is given by the simulated average first-passage time curves. We find that these curves can be described as power functions containing two parameters, α and β, except near the percolation threshold of gel/fluid or compositional clusters. We find also that the intrinsic molecules are involved in approximately normal diffusion, i.e., β ≈ 2 in the extreme gel and fluid phase regions, while in the gel/fluid and gel/gel mixed phase regions the diffusion is anomalous, i.e., β ≠ 2. In the mixed phase regions, when the initial local state of the diffusing molecule is not specified, each component is involved in sub-diffusion (β > 2). In the gel/fluid mixed phase region molecules situated initially inside a fluid cluster are involved in sub-diffusion, but DMPC molecules situated initially inside a gel cluster are involved in super-diffusion (β < 2). The possibility of anomalous diffusion in membranes apparently arises because the diffusing molecule visits a variety of different environments characterized by its relative proximity to various membrane components. The diffusion is actually anomalous when the components of the bilayer are nonrandomly distributed. The deviation from random distribution is strongly correlated with β. Similar to the results of the NMR experiments, the calculated relative diffusion coefficient continuously decreases in the gel/fluid mixed phase region with decreasing temperature. In apparent contradiction, diffusion measured by fluorescence recovery after photobleaching (FRAP) demonstrates the existence of a threshold temperature, below which long-range diffusion of FRAP probe molecules is essentially blocked. This threshold temperature is highly correlated with the percolation temperature of gel clusters.