Role of cholesterol in the formation and nature of lipid rafts in planar and spherical model membranes
Role of cholesterol in the formation and nature of lipid rafts in planar and spherical model membranes
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DOI：
10.1016/s0006-3495(04)74347-7
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发表时间：
2004-05-01
影响因子：
3.4
通讯作者：
Tamm, LK
中科院分区：
文献类型：
--
作者：
Crane, JM;Tamm, LK
甾醇在真核细胞膜的横向组织中发挥着至关重要的调节和结构作用。胆固醇与哺乳动物细胞膜中有序脂质结构域（筏）的可能形成有关。脂筏由液态有序 (l(o)) 相的脂质组成，并被液态无序 (l(d)) 相的脂质包围。胆固醇和鞘磷脂被认为是细胞膜和模型膜中脂筏的主要成分。我们在由猪脑磷脂酰胆碱（bPC）、猪脑鞘磷脂（bSM）和胆固醇组成的平面支持的脂质双层中使用荧光显微镜和光漂白后的荧光恢复来绘制l（d）/l（o）相共存的组成依赖性。胆固醇会降低 bPC 双层的流动性，但会破坏 bSM 的高度有序的凝胶相，从而形成更具流动性的膜。当与 bPC/bSM (1:1) 或 bPC/bSM (2:1) 混合时，胆固醇会诱导 l(o) 相域的形成。发现 l(o) 相中的膜分数与两种磷脂混合物中的胆固醇浓度成正比，这意味着 bPC 的很大一部分共偏析到 l(o) 相域中。图像揭示了渗滤阈值，即当总膜的 45-50% 转化为 lo 相时，筏连接且流体域断开的点。在室温下，这种情况发生在 1:1 bPC/bSM 双层中 20 至 25 mol% 胆固醇之间以及 2:1 bPC/bSM 双层中 25 至 30 mol% 胆固醇之间； 37°C 1:1 bPC/bSM 双层中含有 35 mol% 胆固醇。通过荧光共振能量转移方法在多层脂质体中获得的 l(o) 相脂质的面积分数证实并支持了在平面脂质双层中获得的结果。
Sterols play a crucial regulatory and structural role in the lateral organization of eukaryotic cell membranes. Cholesterol has been connected to the possible formation of ordered lipid domains (rafts) in mammalian cell membranes. Lipid rafts are composed of lipids in the liquid- ordered (l(o)) phase and are surrounded with lipids in the liquid- disordered (l(d)) phase. Cholesterol and sphingomyelin are thought to be the principal components of lipid rafts in cell and model membranes. We have used fluorescence microscopy and fluorescence recovery after photobleaching in planar supported lipid bilayers composed of porcine brain phosphatidylcholine (bPC), porcine brain sphingomyelin (bSM), and cholesterol to map the composition-dependence of l(d)/l(o) phase coexistence. Cholesterol decreases the fluidity of bPC bilayers, but disrupts the highly ordered gel phase of bSM, leading to a more fluid membrane. When mixed with bPC/bSM (1:1) or bPC/ bSM (2:1), cholesterol induces the formation of l(o) phase domains. The fraction of the membrane in the l(o) phase was found to be directly proportional to the cholesterol concentration in both phospholipid mixtures, which implies that a significant fraction of bPC cosegregates into l(o) phase domains. Images reveal a percolation threshold, i.e., the point where rafts become connected and fluid domains disconnected, when 45-50% of the total membrane is converted to the lo phase. This happens between 20 and 25 mol % cholesterol in 1:1 bPC/bSM bilayers and between 25 and 30 mol % cholesterol in 2:1 bPC/ bSM bilayers at room temperature, and at; 35 mol % cholesterol in 1:1 bPC/bSM bilayers at 37degreesC. Area fractions of l(o) phase lipids obtained in multilamellar liposomes by a fluorescence resonance energy transfer method confirm and support the results obtained in planar lipid bilayers.