Department of Electronic Science, Fujian Research Center for Solid-State Lighting, Xiamen University, Xiamen 361005, China.
Department of Chemistry and Physics, La Trobe Institute for Molecular Science (LIMS), La Trobe University, Melbourne, Victoria 3086, Australia.
J Phys Chem Lett. 2020 Nov 5;11(21):9476-9484. doi: 10.1021/acs.jpclett.0c02192. Epub 2020 Oct 27.
Cholesterol is believed to induce the formation of membrane domains, "rafts", which are implicated in a range of natural and pathologic membrane processes. Therefore, it is important to understand the role that cholesterol plays in the formation of these structures. Here, we use label-free spectroscopic imaging to investigate cholesterol fractioning in supported bilayer membranes at nanoscale. Scattering-type scanning near-field optical microscopy (s-SNOM) was used to visualize the formation of cholesterol-induced domains in 1,2-dimyristoyl--glycero-3-phosphocholine (DMPC) membranes. Our results revealed the coexistence of phase separated domains in DMPC lipids with 10 mol % cholesterol content, whereas a mostly homogeneous bilayer was found at low (5 mol %) and high (15 mol %) cholesterol content. Near-field nano-FTIR spectroscopy was used to identify the cholesterol-rich domains based on their qualitative chemical compositions. It was determined that cholesterol binds to phosphodiester and alkyl glycerol ester moieties, likely via hydrogen bonding of the alcohol to either of the ester oxygens. The results also confirm the existence of an ideal cholesterol-lipid mixture ratio (∼15:85) with a geometrically defined packing. At lower cholesterol content there is phase separation between liquid ordered and almost neat DMPC domains. Thus, the liquid ordered phase exists at an energy minimum at a given lipid-cholesterol ratio.
胆固醇被认为会诱导膜域（“筏”）的形成，这些膜域与一系列自然和病理膜过程有关。因此，了解胆固醇在这些结构形成中的作用非常重要。在这里，我们使用无标记光谱成像技术在纳米尺度上研究了支撑双层膜中胆固醇的分馏。散射型扫描近场光学显微镜（s-SNOM）用于可视化 1,2-二肉豆蔻酰基-sn-甘油-3-磷酸胆碱（DMPC）膜中胆固醇诱导结构域的形成。我们的结果表明，在含有 10 mol%胆固醇的 DMPC 脂质中存在相分离的域，而在低（5 mol%）和高（15 mol%）胆固醇含量下则发现大多是均匀的双层。近场纳米傅里叶变换红外光谱（nano-FTIR）用于根据其定性化学成分识别富含胆固醇的域。确定胆固醇与磷酸二酯和烷基甘油酯部分结合，可能通过醇与酯氧原子中的任一个的氢键。结果还证实了存在理想的胆固醇-脂质混合比（约 15:85），具有几何定义的堆积。在较低的胆固醇含量下，液体有序相与几乎纯净的 DMPC 域之间存在相分离。因此，在给定的脂质-胆固醇比下，液体有序相处于能量最小值。
