Membrane nanotubes induced by aqueous phase separation and stabilized by spontaneous curvature
Membrane nanotubes induced by aqueous phase separation and stabilized by spontaneous curvature
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DOI：
10.1073/pnas.1015892108
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发表时间：
2011-03-22
影响因子：
11.1
通讯作者：
Dimova, Rumiana
中科院分区：
文献类型：
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作者：
Li, Yanhong;Lipowsky, Reinhard;Dimova, Rumiana
管状膜结构广泛存在于真核细胞中，但其形成和稳定性的机制还不清楚。以前的工作集中在管挤出细胞和模型膜下施加外力。在这里，我们提出了新的膜/聚合物系统，在没有外部施加的力的情况下形成稳定的管。两种水溶性聚合物，聚乙二醇和葡聚糖的溶液，封装在巨大的脂质囊泡，细胞大小的模型系统。高渗放气引起封闭溶液的相分离。在放气过程中产生的多余膜面积储存在囊泡内的大量膜纳米管中。管的直径低于光学分辨率，并且仅在荧光标记时才可见。这些管子相当稳定：在没有外力的情况下，它们存在了好几天。对瘪泡形状的理论分析表明，如果膜没有自发弯曲，这些形状将是不稳定的。使用管直径和囊泡的总体尺寸之间的长度尺度的大分离，可以计算自发曲率，并且发现对于一定范围的聚合物浓度，自发曲率为约-1/（240 nm）。纳米管也可以通过微吸管抽吸囊泡来增加膜张力而缩回到母囊泡中。膜管，可以形成和收回容易，应该是相关的脂质储存在细胞中。
Tubular membrane structures are widespread in eukaryotic cells, but the mechanisms underlying their formation and stability are not well understood. Previous work has focused on tube extrusion from cells and model membranes under the application of external forces. Here, we present novel membrane/polymer systems, where stable tubes form in the absence of externally applied forces. Solutions of two water-soluble polymers, polyethylene glycol and dextran, were encapsulated in giant lipid vesicles, cell-size model systems. Hypertonic deflation induced phase separation of the enclosed solution. The excess membrane area created during the deflation process was stored in a large number of membrane nanotubes inside the vesicle. The tubes had a diameter below optical resolution and became visible only when fluorescently labeled. The tubes were rather stable: In the absence of external forces, they existed for several days. A theoretical analysis of the shapes of the deflated vesicles reveals that these shapes would be unstable if the membranes had no spontaneous curvature. Using the large separation of length scales between the tube diameter and the overall size of the vesicles, the spontaneous curvature can be calculated and is found to be about -1/(240 nm) for a certain range of polymer concentrations. The nanotubes could also be retracted back into the mother vesicle by increasing the membrane tension via micropipette aspiration of the vesicle. Membrane tubes, which can form and be retracted easily, should be relevant for lipid storage in cells.