Lipid rafts and their analytical methods

Abstract

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-β-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.