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Mode Specific Elastic Constants for the Gel Liquid-Ordered and Liquid-Disordered Phases of DPPC/DOPC/Cholesterol Model Lipid Bi-layers

机译：DppC / DOpC /胆固醇脂质模型双层的模式的具体弹性常数为凝胶液体有序和液 - 无序相

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摘要

Using a microscopic molecular theory, we determine the bending and saddle-splay constants of three-component lipid bilayers. The membrane contains cholesterol, dipalmitoyl-phophatidylcholine (DPPC), and dioleoylphosphatidylcholine (DOPC) and the predictions of the theory have been shown to qualitatively reproduce phase diagrams of giant unilamellar vesicles (GUVs) of the same three components. The bending and saddle-splay constants were calculated for gel, liquid-ordered (lo), and liquid-disordered (ld) phases. By proper expansion of the free energy, the molecular theory enables us to determine the effects of the mode of membrane bending deformation on the value of the elastic constants for different phases. In particular, we refer to the ability of the molecules to arrange the composition between the two monolayers upon deformation. The bending and saddle-splay constants obtained from the free energy expansion can be expressed in terms of moments of the local lateral pressures and their derivatives all evaluated for a symmetric planar bilayer. The effect of blocked vs free exchange of lipids across the two monolayers on the values of the bending constant is as high as 50 kBT in the ld phase to as high as 200 kBT in the lo phase. These results show that one must strongly consider the mode of deformation in determining the mechanical properties of lipid bilayers. We discuss how the different contributions to the lateral pressures affect the values of the elastic constants including the effects of cholesterol concentration and temperature on the membrane elastic constants. We also calculate the equilibrium binding concentrations of lipid tail anchors as a function of membrane curvature by explicitly determining the chemical potential difference of species across a curved bilayer. Our results are in excellent agreement with recent experimental results.
机译：使用微观分子理论，我们确定三组分脂质双层的弯曲和鞍形张开常数。该膜包含胆固醇，二棕榈酰磷脂酰胆碱（DPPC）和二油酰磷脂酰胆碱（DOPC），并且该理论的预测已定性地再现了具有相同三个成分的巨型单层囊泡（GUV）的相图。计算了凝胶相，液相序（Io）和液相序（Id）相的弯曲常数和鞍形张开常数。通过自由能的适当扩展，分子理论使我们能够确定膜弯曲变形模式对不同相的弹性常数值的影响。特别地，我们指的是分子在变形时将组成物布置在两个单层之间的能力。从自由能膨胀中获得的弯曲和鞍形展开常数可以用局部侧向压力的矩表示，并且它们的导数全部针对对称平面双层进行评估。跨两个单层的脂质的阻断与自由交换对弯曲常数的影响在ld相中高达50 kBT，在lo相中高达200 kBT。这些结果表明，在确定脂质双层的机械性能时，必须强烈考虑变形模式。我们讨论了对侧向压力的不同贡献如何影响弹性常数的值，包括胆固醇浓度和温度对膜弹性常数的影响。我们还通过明确确定跨弯曲双层的物种的化学势差来计算脂质尾锚的平衡结合浓度作为膜曲率的函数。我们的结果与最近的实验结果非常吻合。

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  • 作者

    Mark J. Uline; Igal Szleifer;

  • 作者单位
  • 年(卷),期 -1(161),-1
  • 年度 -1
  • 页码 177–303
  • 总页数 18
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