Mardešić Ivan, Boban Zvonimir, Subczynski Witold Karol, Raguz Marija
Department of Medical Physics and Biophysics, University of Split School of Medicine, 21000 Split, Croatia.
Faculty of Science, University of Split, Doctoral Study of Biophysics, 21000 Split, Croatia.
Membranes (Basel). 2023 Mar 10;13(3):320. doi: 10.3390/membranes13030320.
Cholesterol (Chol) is an essential component of animal cell membranes and is most abundant in plasma membranes (PMs) where its concentration typically ranges from 10 to 30 mol%. However, in red blood cells and Schwann cells, PMs Chol content is as high as 50 mol%, and in the PMs of the eye lens fiber cells, it can reach up to 66 mol%. Being amphiphilic, Chol molecules are easily incorporated into the lipid bilayer where they affect the membrane lateral organization and transmembrane physical properties. In the aqueous phase, Chol cannot form free bilayers by itself. However, pure Chol bilayer domains (CBDs) can form in lipid bilayer membranes with the Chol content exceeding 50 mol%. The range of Chol concentrations surpassing 50 mol% is less frequent in biological membranes and is consequently less investigated. Nevertheless, it is significant for the normal functioning of the eye lens and understanding how Chol plaques form in atherosclerosis. The most commonly used membrane models are unilamellar and multilamellar vesicles (MLVs) and supported lipid bilayers (SLBs). CBDs have been observed directly using confocal microscopy, X-ray reflectometry and saturation recovery electron paramagnetic resonance (SR EPR). Indirect evidence of CBDs has also been reported by using atomic force microscopy (AFM) and fluorescence recovery after photobleaching (FRAP) experiments. The overall goal of this review is to demonstrate the advantages and limitations of the various membrane models and experimental techniques suitable for the detection and investigation of the lateral organization, function and physical properties of CBDs.
胆固醇（Chol）是动物细胞膜的重要组成部分，在质膜（PMs）中含量最为丰富，其浓度通常在10%至30%（摩尔分数）之间。然而，在红细胞和施万细胞中，质膜的胆固醇含量高达50%（摩尔分数），而在眼晶状体纤维细胞质膜中，这一含量可达66%（摩尔分数）。由于具有两亲性，胆固醇分子很容易融入脂质双层，在其中影响膜的侧向组织和跨膜物理性质。在水相中，胆固醇自身无法形成游离双层。然而，当胆固醇含量超过50%（摩尔分数）时，脂质双层膜中可形成纯胆固醇双层结构域（CBDs）。胆固醇浓度超过50%（摩尔分数）的范围在生物膜中较少见，因此相关研究也较少。尽管如此，这对于眼晶状体的正常功能以及理解动脉粥样硬化中胆固醇斑块的形成具有重要意义。最常用的膜模型是单层和多层囊泡（MLVs）以及支撑脂质双层（SLBs）。已通过共聚焦显微镜、X射线反射法和饱和恢复电子顺磁共振（SR EPR）直接观察到CBDs。通过原子力显微镜（AFM）和光漂白后荧光恢复（FRAP）实验也报道了CBDs的间接证据。本综述的总体目标是展示适用于检测和研究CBDs侧向组织、功能及物理性质的各种膜模型和实验技术的优缺点。
