Hoekstra D, Martin O C
Biochemistry. 1982 Nov 23;21(24):6097-103. doi: 10.1021/bi00267a011.
The effect of membrane fusion on the transbilayer distribution of dioleoyl- and dipalmitoylphosphatidylethanolamine (DOPE and DPPE, respectively) in phosphatidylserine (PS) vesicles was investigated. A 7-fold increase in the external pool of DOPE, as determined by labeling of the vesicle surface with 2,4,6-trinitrobenzenesulfonic acid, was observed when multilamellar vesicles (MLV) consisting of PS and DOPE were incubated with small unilamellar vesicles (SUV) of PS in the presence of Ca2+. In contrast, no significant redistribution of DPPE was seen when similar experiments were performed by using PS bilayers that contained DPPE instead of DOPE. Redistribution of neither DOPE nor DPPE could be detected during SUV-SUV fusion. By using the resonance energy transfer fusion assay for mixing of membrane lipids [Struck, D.K., Hoekstra, D., & Pagano, R. E. (1981) Biochemistry 20, 4093-4099; Hoekstra, D. (1982) Biochemistry 21, 2833-2840], it was demonstrated that fusion between SUV and MLV had actually occurred. The results also suggested that (partial) fusion of internal bilayers within the multilamellar system must have occurred. Although Mg2+-induced fusion between SUV and MLV was also observed, no redistribution of DOPE was seen in this case. It is concluded that the observed translocation of DOPE during fusion was probably mediated via inverted micellar structures, which were formed when the lipid was converted to the hexagonal (HII) phase resulting from lipid phase separation between PS and DOPE. However, induction of the hexagonal phase per se, i.e., in the absence of fusion, did not cause substantial transbilayer redistribution of DOPE, suggesting that fusion was intimately involved in this phenomenon. It is suggested that fusion represents the "driving force" for transbilayer DOPE redistribution, requiring a (partial) overlap between the kinetics of phase separation and fusion.
研究了膜融合对磷脂酰丝氨酸（PS）囊泡中二油酰基磷脂酰乙醇胺和二棕榈酰基磷脂酰乙醇胺（分别为DOPE和DPPE）跨膜分布的影响。当由PS和DOPE组成的多层囊泡（MLV）在Ca2+存在下与PS的小单层囊泡（SUV）孵育时，通过用2,4,6-三硝基苯磺酸标记囊泡表面测定，DOPE的外部池增加了7倍。相比之下，当使用含有DPPE而非DOPE的PS双层进行类似实验时，未观察到DPPE的显著重新分布。在SUV-SUV融合过程中，未检测到DOPE和DPPE的重新分布。通过使用用于膜脂混合的共振能量转移融合测定法[Struck, D.K., Hoekstra, D., & Pagano, R. E. (1981) Biochemistry 20, 4093 - 4099; Hoekstra, D. (1982) Biochemistry 21, 2833 - 2840]，证明SUV和MLV之间实际上发生了融合。结果还表明，多层系统内内部双层的（部分）融合一定已经发生。虽然也观察到Mg2+诱导的SUV和MLV之间的融合，但在这种情况下未观察到DOPE的重新分布。得出的结论是，融合过程中观察到的DOPE易位可能是通过反胶束结构介导的，当脂质由于PS和DOPE之间的脂质相分离而转变为六方（HII）相时形成反胶束结构。然而，六方相本身的诱导，即在没有融合的情况下，并没有导致DOPE的大量跨膜重新分布，这表明融合与这一现象密切相关。有人提出，融合代表了DOPE跨膜重新分布的“驱动力”，需要相分离动力学和融合动力学之间的（部分）重叠。
