Comparison of confined water in Ld- and Lo-phases of cholesterol/lecithin mixtures

众所周知，胆固醇影响脂质双层的结构性质，如流动性、曲率和脂质堆积，同时也影响完整膜蛋白的位置。在多组分的脂类混合物中，胆固醇可以导致液体无序的LO相和液体有序的LO相之间的相分离。在DOPC、DSPC和胆固醇的三元混合物中，在临界温度TC以下，贫胆固醇的LD相和富含胆固醇的LO相共存，而在TC以上，两相合并形成单一的、均匀的LD相。而胆固醇对双层结构的作用已经得到了很好的研究，而对承压水与脂双层界面相互作用的影响却鲜有人探讨。重新访问Heftberger等人的一项研究的数据。(1)，我们应用了最近发表的“三水层”模型(见图1)(2)。本研究的目的是确定层叠双层膜在LO相和LD相的脂/水界面的精细结构。为了获得对(I)头基相关、(Ii)扰动和(Iii)自由水区的第一次洞察，我们确定了这些水层作为温度的函数的变化，并比较了不同脂肪/胆固醇浓度的结果。

Cholesterol is known to affect structural properties of lipid bilayers, such as fluidity, curvature, and lipid packing, while also affecting the position of integral membrane proteins. In multi-component lipid mixtures, cholesterol can induce a phase separation between liquid-disordered Ld and liquid-ordered Lo phases. In a ternary mixture of DOPC, DSPC and cholesterol, both cholesterol-poor Ld and cholesterol-rich Lo phases coexist below a critical temperature TC, while above TC, both phases coalesce to form a single, homogeneous Ld phase. While cholesterol's role on the bilayer structure has been well-studied, whereas influence on the interactions between confined-water and the lipid bilayer interface is scarcely explored. Revisiting data from a study by Heftberger et al. (1), we applied a recently published 'three-water layer' model (see Figure 1)(2). The aim of this study was to determine the fine structure at the lipid/water interface of stacked bilayers, both in the Lo and Ld phase. To obtain first insights into the (i) headgroup associated, (ii) perturbed and (iii) free water regions, we determined the changes to these water layers as a function of temperature and comparing results for different lipid/cholesterol concentrations.