Patterns of Flexible Nanotubes Formed by Liquid-Ordered and Liquid-Disordered Membranes
Patterns of Flexible Nanotubes Formed by Liquid-Ordered and Liquid-Disordered Membranes
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DOI：
10.1021/acsnano.5b05377
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发表时间：
2016-01-01
期刊：
影响因子：
17.1
通讯作者：
Lipowsky, Reinhard
中科院分区：
文献类型：
--
作者：
Liu, Yonggang;Agudo-Canalejo, Jaime;Lipowsky, Reinhard
生物膜形成细胞内和细胞间纳米管，用于单细胞内的分子分选以及不同细胞之间的长距离连接。这种纳米管也可以由液态的合成脂质双层发展而来。每个纳米管都具有很大的面积与体积比，并稳定地包围着水通道，从而与周围环境隔绝。这些管子相当灵活，可以很容易地改变它们的长度和构造。在这里，我们研究了由液体有序（Lo）和液体无序（Ld）膜形成的纳米管，其中三种脂质成分暴露于聚乙二醇（PEG）和葡聚糖两种聚合物的水性混合物中。当我们通过渗透放气减少巨型囊泡的体积，从而将膜的两个双层小叶暴露于不同成分的聚合物溶液时，两种类型的膜都会形成引人注目的纳米管图案。随着体积的减小，观察到三种不同的模式，对应于三种不同的囊泡形态，反映了自发曲率和水相分离的相互作用。我们表明，管的成核和生长受两个动力学途径控制，并且管在一定的临界管长度下经历了从项链状管到圆柱形管的新颖形状转变。我们使用三种不同且独立的图像分析方法从观察到的囊泡形态推断出膜-聚合物相互作用产生的自发曲率。发现 Ld 膜的自发曲率是 Lo 膜的 4.7 倍。我们还表明，这些曲率是由膜上的 PEG 弱吸附产生的，每条链的结合亲和力约为 1.6 k(B)T。通过这种方式，我们的研究提供了纳米级膜形状和分子相互作用之间的直接联系。我们的方法相当通用，可以应用于许多其他感兴趣的系统，例如聚合物囊泡或膜结合蛋白和肽。
Biological membranes form both intra- and intercellular nanotubes that are used for molecular sorting within single cells and for long-distance connections-between different cells. Such nanotubes can also develop from synthetic lipid bilayers in their fluid state. Each nanotube has a large areaf-to-volume ratio and stably encloses a water channel that is thereby shielded from its surroundings. The tubes are rather flexible and can easily change both their length and their conformation. Here, we study nanotubes formed by liquid-ordered (Lo) and liquid-disordered (Ld) membranes with three lipid components exposed to aqueous mixtures of two polymers, polyethylene glycol (PEG) and dextran. Both types of membranes form striking patterns of nanotubes when we reduce the volume of giant vesicles by osmotic deflation, thereby exposing the two bilayer leaflets of the membranes to polymer solutions of different composition. With decreasing volume, three different patterns are observed corresponding to three distinct vesicle morphologies that reflect the interplay of spontaneous curvature and aqueous phase separation. We show that tube nucleation and growth is governed by two kinetic pathways and that the tubes undergo a novel shape transformation from necklace-like to cylindrical tubes at a certain critical tube length. We-deduce the spontaneous curvature generated by the membrane-polymer interactions from the observed vesicle morphologies using three different and independent methods of image analysis. The spontaneous curvature of the Ld membranes is found to be 4.7 times larger than that of the Lo membranes. We also show that these curvatures are generated by weak PEG adsorption onto the membranes, with a binding affinity of about 1.6 k(B)T per chain. In this way, our study provides a direct connection between nanoscopic membrane shapes and molecular interactions. Our approach is rather general and can be applied to many other systems of interest such as polymersomes or membrane-bound proteins and peptides.