Organization of glycosphingolipids in bilayers and plasma membranes of mammalian cells.
Organization of glycosphingolipids in bilayers and plasma membranes of mammalian cells.
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哺乳动物细胞双层和质膜中鞘糖脂的组织。
DOI：
10.1146/annurev.bb.14.060185.002045
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
T. Tillack
中科院分区：
文献类型：
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作者：
T. E. Thompson;T. Tillack
在这篇评论中提出的证据强烈表明，当作为液晶磷脂双层中的次要组分存在时，中性鞘糖脂被分离成分散在基质磷脂中的小尺寸的组成域。在许多情况下，分散结构域中的鞘糖脂处于凝胶状态。由于这些结构域处于凝胶状态，单个分子从双层表面逃逸的速度非常缓慢，比磷脂组分慢得多。目前还没有直接证据表明这种缓慢的逃逸速率是生物膜双层中中性糖脂的一种特性。然而，如果是这样，那么这些分子非常适合它们作为细胞表面标记物的假定作用，这一作用涉及它们在许多重要的生物学功能中的作用。有证据表明，这种类型的分子也存在于至少一些哺乳动物细胞质膜外表面上的分散的微区结构中。当从细胞表面附近的环境介质观察时，这些糖脂的小结构域及其从细胞表面向外突出的糖残基非常像大的膜糖蛋白。因此，无论糖残基是糖蛋白还是糖脂来源的，它们都定位于细胞外表面上的组或块。这种贴片结构的一个重要结果可能是对配体与贴片结合的自由能的明显影响。无论配体是单价还是多价，表面补丁中糖的浓度约为2M将导致表观配体结合自由能显著大于表面上单个分离的糖残基的结合自由能。与中性鞘糖脂（和硫苷脂，也许）的现有信息表明，神经节苷脂不局限于小域模型系统中，最有可能不是在生物膜。这种类型的鞘糖脂的封端似乎在某些情况下确实发生。然而，几乎可以肯定的是，加帽不是神经节苷脂磷脂双层系统的固有特性。虽然在37摄氏度神经节苷脂迅速从胶束转移到磷脂囊泡和细胞膜上，但对这类分子离开磷脂双层的速率一无所知。它们在细胞表面的已知生物学功能似乎要求它们非常缓慢地离开，如果有的话，中性鞘糖脂也是如此。鞘糖脂由于其多糖部分是一类独特的脂质和细胞表面组分。（400字处截断摘要）
The evidence presented in this review strongly suggests that, when present as a minor component in liquid crystalline phospholipid bilayers, neutral glycosphingolipids are segregated into compositional domains of small size dispersed in the matrix phospholipid. In many instances the glycosphingolipid in the dispersed domains is in the gel state. Because these domains are in the gel state, the individual molecules escape only very slowly from the surface of the bilayer, much more slowly than do the phospholipid components. There is as yet no direct evidence that this slow escape rate is a property of neutral glycolipids in biological membrane bilayers. If it is, however, then these molecules are well suited for their putative role as cell surface markers, a role that involves them in many important biological functions. There is evidence to suggest that molecules of this type are also present in a dispersed microdomain structure on the external surface of at least some mammalian cell plasma membranes. These small domains of glycolipids with their sugar residues projecting outward from the cell surface are much like a large membrane glycoprotein when viewed from the ambient medium near the cell surface. Thus, whether the sugar residues be of glycoprotein or glycolipid origin, they are localized in groups or patches on the external surface of the cell. One important consequence of this patch structure may be in the obvious effect on the free energy of binding a ligand to a patch. Whether the ligand is mono- or polyvalent, the roughly 2 M concentration of sugar in the surface patch will cause the apparent ligand binding free energy to be substantially larger than it would be for a single isolated sugar residue on the surface. In contrast to the neutral glycosphingolipids (and sulfatides, perhaps) the available information suggests that gangliosides are not localized in small domains in model systems and most probably not in biological membranes. Capping of this type of glycosphingolipid does appear to occur under certain circumstances. However, it is almost certain that capping is not an intrinsic property of ganglioside phospholipid-bilayer systems. Although at 37 degrees C gangliosides rapidly transfer from micelles to phospholipid vesicles and to cell membranes, nothing is known about the rates at which this class of molecules leave a phospholipid bilayer. Their known biological functions on the cell surface appear to require that they leave very slowly, if at all, as do the neutral glycosphingolipids. The glycosphingolipids are, by virtue of their polysaccharide moeity, a unique class of lipids and cell surface components.(ABSTRACT TRUNCATED AT 400 WORDS)