Quantification of Aminophospholipid Asymmetry in Supported Lipid Bilayers by Neutron Reflectometry

细胞膜是基于脂质双分子层，表现出复杂的组成和组织。在健康细胞中，脂质在双分子层的两个小叶之间的分布是不对称的：磷脂酰丝氨酸（PS）局限于膜的内小叶，而外小叶主要由磷脂酰胆碱和鞘磷脂组成。脂质也是横向组织的，在几十纳米的长度尺度上具有异质性。这些是如何产生的尚不清楚，因为通常用于模拟细胞膜的典型的高熔点、低熔点、磷脂酰胆碱的胆固醇混合物表现出具有um大小结构域的宏观相分离。能够同时捕捉脂质组织的横向和横向方面的模型系统很少，因此，研究细胞膜中脂质组织的两个方面如何相互耦合一直很困难。我们开发了一个模型系统来捕捉这两个特征。它基于TiO2上的负载脂质双分子层（slb），包含高熔点、低熔点、高胆固醇的磷脂酰胆碱混合物和不对称分布的PS。当前工作的目标是通过中子反射法（NR）量化这些不对称细胞膜模拟物中的脂质分布，以便进一步研究这些系统中的相行为和脂质扩散。

Cell membranes are based on lipid bilayers that exhibit complex composition and organization. In healthy cells, the distribution of lipids between the two leaflets of the bilayer is asymmetric: phosphatidyl serine (PS) is restricted to the inner leaflet of the membrane, while the outer leaflet is predominantly composed of phosphatidyl choline and sphingomyelin. Lipids are also organized laterally, with heterogeneities on the lengthscale of tens of nm. How these arise is not clear, because the canonical high-melting, low-melting, cholesterol mixtures of phosphatidylcholines commonly used to model cell membranes exhibit macroscopic phase separation with um-size domains. Model systems that can capture both the lateral and the transverse aspects of lipid organization are scarce, and for that reason, studying how the two aspects of lipid organization in cell membranes couple to each other has been difficult. We developed a model system that captures both these features. It is based on supported lipid bilayers (SLBs) on TiO2 that contain the high-melting, low-melting, cholesterol mixture of phosphatidyl cholines, and PS, that is distributed asymmetrically. The goal of the current work is to quantify lipid distribution in these asymmetric cell membrane mimics by neutron reflectometry (NR) so that further studies of phase behavior and lipid diffusion in these systems could be carried out.