The cell membrane is an inhomogeneous system composed of phospholipids, sterols and proteins that can be directly attached to underlying cytoskeleton. The linkers between the membrane and the cytoskeleton are believed to have a profound effect on the mechanical properties of the cell membrane and its ability to reshape. Here we investigate the role of membrane-cortex linkers on the extrusion of membrane tubes using computer simulations and experiments. In simulations we find that the force for tube extrusion has a non-linear dependence on the density of membrane-cortex attachments: at a wide range of low and intermediate densities of linkers the force is not significantly influenced by the presence of membrane linking proteins and resembles that of the bare membrane. For large concentrations of linkers however the force substantially increases compared to the bare membrane. In both cases the linkers provided membrane tubes with increased stability against coalescence. We then pulled tubes from HEK cells using optical-tweezers for varying expression levels of the membrane-cortex attachment protein Ezrin. In line with simulations, we observed that overexpression of Ezrin led to an increased extrusion force, while Ezrin depletion had negligible effect on the force. Our results shed new light on the importance of local effects in membrane reshaping at the nanoscopic scales.

中文翻译：

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膜皮层接头对膜管挤出的影响

细胞膜是由磷脂，固醇和蛋白质组成的非均质系统，可以直接附着在其下的细胞骨架上。人们认为，膜与细胞骨架之间的接头对细胞膜的机械性能及其重塑能力具有深远的影响。在这里，我们使用计算机模拟和实验研究膜-皮质接头在膜管挤出中的作用。在模拟中，我们发现管材挤压的力与膜-皮层附着的密度呈非线性关系：在各种低密度和中等密度的接头中，该力不受膜连接蛋白和类似于裸膜。然而，对于高浓度的接头，与裸膜相比，力显着增加。在这两种情况下，接头为膜管提供了增强的抗聚结稳定性。然后，我们使用光镊从HEK细胞中抽出试管，以改变膜皮层附着蛋白Ezrin的表达水平。与模拟一致，我们观察到Ezrin的过度表达导致挤出力增加，而Ezrin耗竭对该力的影响可忽略不计。我们的结果为纳米尺度的膜重塑中局部作用的重要性提供了新的思路。然后，我们使用光镊从HEK细胞中抽出试管，以改变膜皮层附着蛋白Ezrin的表达水平。与模拟一致，我们观察到Ezrin的过度表达导致挤出力增加，而Ezrin耗竭对该力的影响可忽略不计。我们的结果为纳米尺度的膜重塑中局部作用的重要性提供了新的思路。然后，我们使用光镊从HEK细胞中抽出试管，以改变膜皮层附着蛋白Ezrin的表达水平。与模拟一致，我们观察到Ezrin的过度表达导致挤出力增加，而Ezrin耗竭对该力的影响可忽略不计。我们的结果为纳米尺度的膜重塑中局部作用的重要性提供了新的思路。