Anisotropic motion and molecular dynamics of cholesterol, lanosterol, and ergosterol in lecithin bilayers studied by quasi-elastic neutron scattering
Anisotropic motion and molecular dynamics of cholesterol, lanosterol, and ergosterol in lecithin bilayers studied by quasi-elastic neutron scattering
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DOI：
10.1021/bi0201670
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发表时间：
2002-10-29
期刊：
影响因子：
2.9
通讯作者：
Bayerl, TM
中科院分区：
文献类型：
--
作者：
Endress, E;Heller, H;Bayerl, TM
采用准弹性中子散射（QENS）方法研究了三种结构相似的甾醇分子的动力学行为。胆固醇、羊毛甾醇和麦角甾醇。定向双层二棕榈酰磷脂酰胆碱（DPPC）进行了研究，在40摩尔%的甾醇含量和在三个温度（20，36，和50 degreesC）的两个能量分辨率。数据分析集中在直接比较的平面外和平面内的三个甾醇的高频运动的速率和幅度。三种甾醇在两个方向上的（空间受限的）扩散运动的特征在于扩散常数在（5-30）x 10（-12）m（2）s（-1）的范围内，沿膜法线沿着的扩散速率明显更快，导致扩散各向异性，D-a。在低温（20 ℃）下，胆固醇的D-a值最高（4.5），而羊毛甾醇的D-a值最低（2.0）。在高温（50 ℃）下，麦角甾醇扩散具有最高的扩散各向异性（D-a = 2.0），与羊毛甾醇（D-a = 1.8）和胆固醇（D-a = 1.6）相比。最有趣的是，胆固醇在所有三个温度下都显示出1.0-1.1 nm的平面外运动幅度，比其他两种甾醇测量的幅度高出3倍以上。这一发现表明，胆固醇分子的短烷基链可能会在高频率的双层中平面交叉，而其他两个甾醇保持限制在每个单层小叶的几何限制。结果提供了一个例子，甾醇的轻微结构改变可以影响其分子动力学的双层，这反过来可能是相关的膜的微观力学性能。
Quasi-elastic neutron scattering (QENS) was employed to study the molecular dynamics of three structurally related sterols, namely,. cholesterol, lanosterol, and ergosterol. Oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) were investigated at 40 mol % sterol content and at three temperatures (20, 36, and 50 degreesC) for two energy resolutions. Data analysis was concentrated on a direct comparison of the out-of-plane and the in-plane high-frequency motions of the three sterols in terms of their rates and amplitudes. The (spatially restricted) diffusive motion of the three sterols in the two directions was characterized by diffusion constants in the range of (5-30) x 10(-12) m(2) s(-1), with a significantly faster rate of diffusion along the membrane normal, resulting in a diffusional anisotropy, D-a. At low temperature (20 degreesC), cholesterol showed the highest value (D-a = 4.5), while lanosterol gave the lowest one (D-a = 2.0). At high temperature (50 degreesC), ergosterol diffusion had the highest diffusion anisotropy (D-a = 2.0) compared to lanosterol (D-a = 1.8) and cholesterol (D-a = 1.6). Most interestingly, cholesterol showed at all three temperatures an amplitude of its out-of-plane-motion of 1.0-1.1 nm, more than a factor of 3 higher than measured for the other two sterols. This finding suggests that the short alkyl chain of the cholesterol molecule may cross at high frequency the bilayer midplane, while the other two sterols remain confined within the geometrical limits of each monolayer leaflet. The results provide an example of how slight structural alterations of sterols can affect their molecular dynamics in bilayers, which in turn may be relevant to the membrane micromechanical properties.