Domain formation in cholesterol-phospholipid membranes exposed to adhesive surfaces or environments
Domain formation in cholesterol-phospholipid membranes exposed to adhesive surfaces or environments
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DOI：
10.1039/c3sm50712b
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发表时间：
2013-01-01
期刊：
影响因子：
3.4
通讯作者：
Weikl, Thomas R.
中科院分区：
文献类型：
--
作者：
Lipowsky, Reinhard;Rouhiparkouhi, Tahereh;Weikl, Thomas R.
胆固醇和单一磷脂的二元混合物中结构域的形成已经研究了很长时间，但这些结构域的性质仍然是一个有争议的问题。这些域的一种解释是，它们产生于膜内的液体有序相和液体无序相的共存。在这里，我们从理论上研究了粘合剂表面和环境对所提出的相行为的影响。膜的粘附或部分支撑导致两个或几个膜片段与其环境表现出不同的分子相互作用，因此对这些环境具有不同的分子亲和力。我们发现，不同环境之间的亲和力对比强烈影响膜的相行为。首先，亲和力对比将结构域形成空间上限制在单个膜区段。第二，这些对比导致在组合物-温度平面中的共存区域划分为不同膜段的不同共存区域。第三，与游离膜的组成范围相比，膜组成的范围总是减小的，对于膜组成的范围，人们可以观察到在膜片段之一中的域形成。此外，小的亲和力对比度代表奇异扰动，因为当亲和力对比度从小的正值变化到小的负值时，相图以不连续的方式变化。所有这些结果都是相当普遍的，因为它们只遵循热力学稳定性，并适用于任何流体-流体共存的双组分膜。除了这些通用的功能，我们还提供了一个计算方案，通过该方案可以明确地计算特定的二元混合物的共存区域的分区，并说明该方案的二元胆固醇-DPPC膜。我们的理论所预测的结构域形成的一般和具体特征都可以通过实验研究得到。
Domain formation in binary mixtures of cholesterol and a single phospholipid has been studied for a long time but the nature of these domains is still a matter of some debate. One interpretation of these domains is that they arise from the coexistence of liquid-ordered and liquid-disordered phases within the membranes. Here, we study the effect of adhesive surfaces and environments on the proposed phase behavior theoretically. The adhesion or partial support of the membranes leads to two or several membrane segments that exhibit different molecular interactions with their environments and, thus, have different molecular affinities to these environments. We show that the affinity contrasts between different environments strongly affect the phase behavior of the membranes. First, the affinity contrasts confine the domain formation spatially to single membrane segments. Second, these contrasts lead to a partitioning of the coexistence region in the composition-temperature plane into distinct coexistence regions for the different membrane segments. Third, the range of membrane compositions, for which one can observe domain formation in one of the membrane segments, is always reduced compared to the composition range of the free membrane. Furthermore, small affinity contrasts represent singular perturbations in the sense that the phase diagrams change in a discontinuous manner as one varies the affinity contrast from small positive to small negative values. All of these results are quite general because they follow from thermodynamic stability alone and apply to any two-component membrane with fluid-fluid coexistence. In addition to these generic features, we also provide a computational scheme, by which one can explicitly calculate the partitioning of the coexistence regions for a specific binary mixture, and illustrate this scheme for binary cholesterol-DPPC membranes. Both the generic and the specific features of domain formation as predicted by our theory are accessible to experimental studies.