LATERAL DIFFUSION AND PERCOLATION IN 2-PHASE, 2-COMPONENT LIPID BILAYERS - TOPOLOGY OF THE SOLID-PHASE DOMAINS INPLANE AND ACROSS THE LIPID BILAYER
LATERAL DIFFUSION AND PERCOLATION IN 2-PHASE, 2-COMPONENT LIPID BILAYERS - TOPOLOGY OF THE SOLID-PHASE DOMAINS INPLANE AND ACROSS THE LIPID BILAYER
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DOI：
10.1021/bi00146a024
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发表时间：
1992-08-11
期刊：
影响因子：
2.9
通讯作者：
THOMPSON, TE
中科院分区：
文献类型：
--
作者：
ALMEIDA, PFF;VAZ, WLC;THOMPSON, TE
光漂白后的荧光恢复（FRAP）最近已被用于检查双组分、两相磷脂酰胆碱双层中共存相的渗滤性质[Vaz，W. L. C.的方法，梅洛，E. C. C.的方法，& Thompson，T. E.（1989）Biophys. J. 56，869-876]。我们现在报告使用FRAP研究两个额外的问题，在类似的系统。第一个是固相障碍物对液相中横向扩散的影响。第二个问题是，是否在一个单一的双层，在一个单层的固相域是完全叠加在固体域的并列单层。为了解决第一个问题，N-（7-硝基苯并氧杂-2，3-二氮唑-4-基）-1-棕榈酰-2-油酰磷脂酰乙醇胺（NBD-POPE），一种探针，只在流体相溶解时，固相和流体相共存，已在混合物N-木蜡酰二氢半乳糖神经酰胺（LigGalCer）/二棕榈酰磷脂酰胆碱（DPPC）的横向扩散进行了研究。流体相的渗滤发生在固相的高质量分数下。这表明，固体域具有中心对称的形状，一个特性，这使得这是一个很好的实验系统，以测试在群岛扩散的理论模拟。结果表明，理论和实验之间的协议是穷人，已经观察到的结果时，障碍是完整的膜蛋白。我们开发了一个有效的介质模型，在两相系统中的扩散，这解释了我们的结果和那些得到的积分蛋白质。 该模型的显着特点是考虑了一个环形区域周围的障碍，脂质更有序的比在体相流体。扩散系数，然后通过扩展自由区模型的两相系统，考虑到这些annuli计算。第二个问题，在LigGalCer/DPPC和二肉豆蔻酰磷脂酰胆碱（DMPC）/二硬脂酰磷脂酰胆碱（DSPC）系统中，通过比较跨越双层的两个单层的流体相可溶的、凝胶相不溶性的脂质衍生物的扩散来检查跨越脂质双层的固相域的组织（NBD-membrane-spanning-phosphatidylethanolamine，NBD-msPE）与仅限于单个单层的探针的性质。在LigGalCer/DPPC，20：80中，单层之一中的固体域的分布与相对单层中的分布无关。相比之下，在DMPC/DSPC，50：50中，一个单层中的固体域正好叠加在存在于相对单层中的固体域上。
Fluorescence recovery after photobleaching (FRAP) has recently been used to examine the percolation properties of coexisting phases in two-component, two-phase phosphatidylcholine bilayers [Vaz, W. L. C., Melo, E. C. C., & Thompson, T. E. (1989) Biophys. J. 56, 869-876]. We now report the use of FRAP to study two additional problems in similar systems. The first is the effect of solid-phase obstacles on the lateral diffusion in the fluid phase. The second is the question of whether or not, in a single bilayer, solid-phase domains in one monolayer are exactly superimposed on solid domains in the apposing monolayer. To address the first problem, the lateral diffusion of N-(7-nitrobenzoxa-2,3-diazol-4-yl)-1-palmitoyl-2-oleoylphosphatidylethanolamine (NBD-POPE), a probe soluble only in the fluid phase when solid and fluid phases coexist, has been studied in the mixture N-lignoceroyldihydrogalactosylceramide (LigGalCer)/dipalmitoylphosphatidylcholine (DPPC). Percolation of the fluid phase occurs at a high mass fraction of solid phase. This indicates that the solid domains have a centrosymmetric shape, a characteristic which makes this a good experimental system to test theoretical simulations of diffusion in an archipelago. It is shown that agreement between theory and experiment is poor, a result that had already been observed when the obstacles were integral membrane proteins. We develop an effective-medium model for diffusion in two-phase systems which explains both our results and those obtained with integral proteins. The distinctive feature of the model is the consideration of an annular region around the obstacles where the lipids are more ordered than in the bulk fluid phase. The diffusion coefficient is then calculated by extending the free area model to two-phase systems, taking these annuli into account. The second question, the organization of the solid-phase domains across the lipid bilayer, is examined in the systems LigGalCer/DPPC and dimyristoylphosphatidylcholine (DMPC)/distearoylphosphatidylcholine (DSPC) by comparing the diffusion of a fluid-phase-soluble, gel-phase-insoluble lipid derivative which spans the two monolayers of a bilayer (NBD-membrane-spanning-phosphatidylethanolamine, NBD-msPE) with that of a probe which is restricted to a single monolayer. In LigGalCer/DPPC, 20:80, the distribution of solid domains in one of the monolayers is independent of the distribution in the apposing monolayer. In contrast, in DMPC/DSPC, 50:50, the solid domains in one monolayer are exactly superimposed upon the solid domains existing in the apposing monolayer.