Nakahata Norimichi, Ohkubo Satoko
Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
Nihon Yakurigaku Zasshi. 2003 Nov;122(5):419-25. doi: 10.1254/fpj.122.419.
Microdomains in cell membranes consist of caveolae and lipid rafts, in which cholesterol, glycolipids, and sphingomyelin are concentrated. While caveolae are relatively stable because caveolin, an integral protein, supports the structure, lipid rafts are unstable, being dynamically produced and degraded. In lipid rafts, flotillin is assumed to be one of the specifically located proteins. Since microdomains contain several signaling molecules, such as transmembrane receptors, they have an important role in receptor-medicated signal transduction. Caveolae or lipid rafts are known to be resistant to non-ionic detergents, such as Triton X-100. Because of this property, they are separated as the detergent-resistant membranes when the Triton X-100-treated cell lysate is subjected to sucrose gradient centrifugation. On the other hand, cholesterol is an essential molecule to maintain microdomain structure. When the cells are treated with cholesterol removing agents, such as methyl-beta-cyclodextrin and filipin, the microdomain in cell membranes is disrupted. Thus, the cholesterol removing agents are utilized to determine whether the microdomain is involved in certain cellular/physiological responses. Recently, green fluorescent protein-tagged protein is used to analyze the localization of the protein in lipid rafts in intact cells. Research on lipid rafts will be helpful for understanding the detailed mechanism of signal transduction and to clarify the molecular basis of several diseases.
细胞膜中的微结构域由小窝和脂筏组成，其中胆固醇、糖脂和鞘磷脂高度富集。小窝相对稳定，因为整合蛋白小窝蛋白支撑着其结构，而脂筏不稳定，处于动态生成和降解过程中。在脂筏中，浮舰蛋白被认为是特异性定位的蛋白之一。由于微结构域包含多种信号分子，如跨膜受体，它们在受体介导的信号转导中发挥着重要作用。已知小窝或脂筏对非离子去污剂（如Triton X-100）具有抗性。由于这一特性，当用Triton X-100处理的细胞裂解物进行蔗糖梯度离心时，它们会作为抗去污剂膜被分离出来。另一方面，胆固醇是维持微结构域结构的必需分子。当细胞用胆固醇去除剂（如甲基-β-环糊精和菲律宾菌素）处理时，细胞膜中的微结构域会被破坏。因此，胆固醇去除剂被用于确定微结构域是否参与某些细胞/生理反应。最近，绿色荧光蛋白标记的蛋白被用于分析完整细胞中该蛋白在脂筏中的定位。对脂筏的研究将有助于理解信号转导的详细机制，并阐明几种疾病的分子基础。
