期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 278, 期 30, 页码 28109-28115出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M302969200
关键词
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Confocal fluorescence microscopy and fluorescence correlation spectroscopy (FCS) have been employed to investigate the lipid spatial and dynamic organization in giant unilamellar vesicles (GUVs) prepared from ternary mixtures of dioleoyl-phosphatidylcholine/sphingomyelin/ cholesterol. For a certain range of cholesterol concentration, formation of domains with raft-like properties was observed. Strikingly, the lipophilic probe 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI-C-18) was excluded from sphingomyelin-enriched regions, where the raft marker ganglioside GM1 was localized. Cholesterol was shown to promote lipid segregation in dioleoyl-phosphatidylcholine-enriched, liquid-disordered, and sphingomyelin-enriched, liquid-ordered phases. Most importantly, the lipid mobility in sphingomyelin-enriched regions significantly increased by increasing the cholesterol concentration. These results pinpoint the key role, played by cholesterol in tuning lipid dynamics in membranes. At cholesterol concentrations > 50 mol%, domains vanished and the lipid diffusion slowed down upon further addition of cholesterol. By taking the molecular diffusion coefficients as a fingerprint of membrane phase compositions, FCS is proven to evaluate domain lipid compositions. Moreover, FCS data from ternary and binary mixtures have been used to build a ternary phase diagram, which shows areas of phase coexistence, transition points, and, importantly, how lipid dynamics varies between and within phase regions.
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