MODULATION OF POLY(ETHYLENE GLYCOL)-INDUCED FUSION BY MEMBRANE HYDRATION - IMPORTANCE OF INTERBILAYER SEPARATION
MODULATION OF POLY(ETHYLENE GLYCOL)-INDUCED FUSION BY MEMBRANE HYDRATION - IMPORTANCE OF INTERBILAYER SEPARATION
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DOI：
10.1021/bi00125a004
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发表时间：
1992-03-17
期刊：
影响因子：
2.9
通讯作者：
LENTZ, BR
中科院分区：
文献类型：
--
作者：
BURGESS, SW;MCINTOSH, TJ;LENTZ, BR
通过挤出技术制备了由具有不同水合特性的脂质组成的大单层囊泡。囊泡由二油酰磷脂酰胆碱与 0.5 mol% 单油酰磷脂酰胆碱或不同摩尔比的二月桂酰磷脂酰乙醇胺组合而成。通过用于内容物混合和渗漏的荧光测定、用于膜混合的荧光脂质探针测定以及用于检测囊泡大小生长的准弹性光散射来揭示融合。随着水合不良的磷脂酰乙醇胺百分比的增加，诱导融合所需的聚乙二醇（PEG）的浓度降低。根据膜相行为的差示扫描量热法研究和 PEG 中相结构的 X 射线衍射监测，得出的结论是 PEG 不会诱导六方相变或层状相分离。来自多层和单层囊泡的 X 射线衍射研究的电子密度分布表明，在 PEG 浓度下，囊泡之间的水层厚度约为 5 埃，在该浓度下，囊泡首先被诱导融合。在这个分离距离下，相邻双层的胆碱头基接近分子接触。由于纯磷脂酰胆碱囊泡在此双层间间距下不融合，因此双层间水层减少至大约2个水分子的临界宽度可能有助于但不足以产生PEG介导的磷脂膜融合。这些结果与该实验室的其他结果的比较还表明，虽然双层之间的紧密接触促进融合，但近分子接触显然对于实现融合并不是绝对必要的。提出了一个暂定模型来解释这些结果。
Large unilamellar vesicles composed of lipids with different hydration properties were prepared by the extrusion technique. Vesicles were composed of dioleoylphosphatidylcholine in combination with either 0.5 mol % monooleoylphosphatidylcholine or different molar ratios of dilauroylphosphatidylethanolamine. Fusion was revealed via a fluorescence assay for contents mixing and leakage, a fluorescent lipid probe assay for membrane mixing, and quasi-elastic light scattering to detect vesicle size growth. As the percentage of poorly hydrating phosphatidylethanolamine increased, the concentration of poly(ethylene glycol) (PEG) required to induce fusion decreased. From differential scanning calorimetry studies of membrane-phase behavior and X-ray diffraction monitoring of phase structure in PEG, it was concluded that PEG did not induce a hexagonal-phase transition or lamellar-phase separation. Electron density profiles derived from X-ray diffraction studies of multi- and unilamellar vesicles indicated that the water layer between vesicles had a thickness of approximately 5 angstrom at PEG concentrations at which vesicles were first induced to fuse. At this distance of separation, the choline headgroups from apposing bilayers are in near-molecular contact. Since pure phosphatidylcholine vesicles did not fuse at this interbilayer spacing, a reduction in the interbilayer water layer to a critical width of approximately 2 water molecules may contribute to but is not sufficient to produce PEG-mediated fusion of phospholipid membranes. Comparison of these results with other results from this laboratory also indicates that, while close contact between bilayers promotes fusion, near-molecular contact is apparently not absolutely necessary to bring about fusion. A tentative model is presented to account for these results.