Molecular dissection of organization and dynamics of lipid domains in biomembranes

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(1) Characterization of lipid probesLysenin is a pore-forming toxin that specifically binds sphingomyelin (SM). The binding of the toxin to the membrane is accompanied by the oligomerization of the protein, leading to pore formation. Although a previous study showed that SM/cholesterol liposomes were 10,000 times more effective than SM liposomes in inhibiting lysenin-induced hemolysis, the role of cholesterol is not precisely clarified. Our results indicate that both cholesterol and the SM/lysenin ratio control the amount of lysenin monomer via altering the state of protein oligomerization, thus affecting hemolysis.Duramycin is a 19 amino acid tetracyclic lantibiotic closely related to cinnamycin, which is known to bind phosphatidyl-ethanolamine (PE). The lipid specificity of duramycin was not established. Our study indicates that both duramycin and cinnamycin exclusively bind to ethanolamine phospholipids in curvature-dependent manner.(2) Regulation of endocytosis by cholesterolCellular cholesterol increases when cells reach confluency in Chinese hamster ovary (CHO) cells. We showed that the endocytic pathways of several fluorescent lipids were altered in cell confluency-dependent manner. The crucial role of cellular cholesterol in cell-confluency dependent endocytosis was suggested. Our results also suggest that cholesterol controls endocytic routes of a subset of membrane lipids through rab11.(3) Regulation of cellular cholesterol homeostasis by endosome lipid domainsUsing D-PDMP and ganglioside GM1, it is shown that the structure alteration of bis (monoacylglycero) phosphate (BMP)-rich late endosome lipid domain plays a crucial role in cellular cholesterol accumulation. We also employed anti-BMP monoclonal antibody to examine the role of BMP domain in cholesterol homeostasis in macrophages.