By study of asymmetric membranes, models of the cell plasma membrane (PM) have improved, with more realistic properties of the asymmetric lipid composition of the membrane being explored. We used hemifusion of symmetric giant unilamellar vesicles (GUVs) with a supported lipid bilayer (SLB) to engineer bilayer leaflets of different composition. During hemifusion, only the outer leaflets of GUV and SLB are connected, exchanging lipids by simple diffusion. aGUVs were detached from the SLB for study. In general these aGUVs are formed with one leaflet that phase-separates into Ld (liquid disordered) + Lo (liquid ordered) phases, and another leaflet with lipid composition that would form a single fluid phase in a symmetric bilayer. We observed that ordered phases of either Lo or Lβ (gel phase) induce an ordered domain in the apposed fluid leaflet that lacks high melting lipids. Results suggest both an inter-leaflet and an intra-leaflet redistribution of cholesterol. We used C-Laurdan spectral images to investigate the lipid packing/order of aGUVs, finding that cholesterol partitions into the induced ordered domains. We suggest this behavior to be commonplace, that when Ld + Lo phase separation occurs in a cell PM exoplasmic leaflet, an induced order domain forms in the cytoplasmic leaflet.

通过对不对称膜的研究，细胞质膜 (PM) 的模型得到了改进，正在探索膜的不对称脂质成分的更真实的特性。我们使用具有支持的脂质双层 (SLB) 的对称巨型单层囊泡 (GUV) 的半融合来设计不同成分的双层小叶。在半融合过程中，只有 GUV 和 SLB 的外叶相连，通过简单的扩散交换脂质。aGUVs 从 SLB 中分离出来进行研究。通常，这些 aGUV 由一个小叶形成，该小叶相分离为 Ld（液体无序）+ Lo（液体有序）相，另一个小叶具有脂质成分，可在对称双层中形成单一流体相。我们观察到 Lo 或 Lβ（凝胶相）的有序相在缺乏高熔点脂质的并列流体小叶中诱导有序结构域。结果表明胆固醇在小叶间和小叶内重新分布。我们使用 C-Laurdan 光谱图像来研究 aGUV 的脂质堆积/顺序，发现胆固醇分为诱导的有序域。我们认为这种行为是司空见惯的，即当细胞 PM 外质小叶中发生 Ld + Lo 相分离时，在细胞质小叶中形成诱导的有序域。