Tilt modulus of a lipid monolayer
Tilt modulus of a lipid monolayer
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DOI：
10.1140/epje/i2004-10019-y
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发表时间：
2004-07-01
影响因子：
1.8
通讯作者：
Kozlov, MM
中科院分区：
文献类型：
--
作者：
May, S;Kozlovsky, Y;Kozlov, MM
除了熟悉的弯曲和拉伸变形，脂质单层和双层在其无序状态下经常受到倾斜变形，例如在伴随膜融合的结构重排中发生，或在“倾斜”疏水蛋白插入脂质双层时发生。我们研究了一个平面的脂质单层倾斜变形的弹性响应，使用的空间和构象平均链端到端的矢量从膜正常定义一个宏观膜倾斜。相应的倾斜模量k（t）的物理起源和大小进行了分析，使用两个互补的理论方法。第一个是一个唯象模型，表明倾斜和弯曲变形是解耦的，链间相关性对倾斜模量的影响很小。第二个是基于分子水平的平均场理论的链包装，使现实的，多构象，链模型的倾斜模量的数值评估。这两种方法表明，倾斜模量涉及两个主要的贡献。第一个是弹性起源，由烃链的拉伸后倾斜变形，并反映链构象自由度的损失与链拉伸。第二，纯粹的熵，贡献的结果由倾斜变形链导向器取向的波动所施加的约束。使用链包装理论，我们计算的两个贡献数值作为每个链的横截面积的函数。的弹性和熵项示出，占主导地位的值的k（t）的小和大面积每个链，分别。对于生物膜中脂链的典型横截面积，它们具有相当的大小，产生的k（t）近似为0.2k（B）T/埃（2）。
In addition to the familiar bending and stretching deformations, lipid monolayers and bilayers in their disordered state are often subjected to tilt deformations, occurring for instance in structural rearrangements accompanying membrane fusion, or upon insertion of "oblique" hydrophobic proteins into lipid bilayers. We study the elastic response of a flat lipid monolayer to a tilt deformation, using the spatial and conformational average of the chain end-to-end vector from the membrane normal to define a macroscopic membrane tilt. The physical origin and magnitude of the corresponding tilt modulus k(t) is analyzed using two complementary theoretical approaches. The first is a phenomenological model showing that the tilt and bending deformations are decoupled and the effects of inter-chain correlations on the tilt modulus is small. The second is based on a molecular-level mean-field theory of chain packing, enabling numerical evaluation of the tilt modulus for realistic, multi-conformation, chain models. Both approaches reveal that the tilt modulus involves two major contributions. The first is elastic in origin, arising from the stretching of the hydrocarbon chains upon a tilt deformation and reflecting the loss of chain conformational freedom associated with chain stretching. The second, purely entropic, contribution results from the constraints imposed by a tilt deformation on the fluctuations of chain director orientations. Using the chain-packing theory we compute the two contributions numerically as a function of the cross-sectional area per chain. The elastic and entropic terms are shown to dominate the value of k(t) for small and large areas per chain, respectively. For typical cross-sectional areas of lipid chains in biological membranes they areof comparable magnitude, yielding k(t) approximate to 0.2k(B)T/Angstrom(2).