García-Sáez Ana J, Chiantia Salvatore, Schwille Petra
Biotechnologisches Zentrum der Techische Universität Dresden, 1307 Dresden, Germany.
Biotechnologisches Zentrum der Techische Universität Dresden, 1307 Dresden, Germany.
J Biol Chem. 2007 Nov 16;282(46):33537-33544. doi: 10.1074/jbc.M706162200. Epub 2007 Sep 11.
The principles of organization and functioning of cellular membranes are currently not well understood. The raft hypothesis suggests the existence of domains or rafts in cell membranes, which behave as protein and lipid platforms. They have a functional role in important cellular processes, like protein sorting or cell signaling, among others. Theoretical work suggests that the interfacial energy at the domain edge, also known as line tension, is a key parameter determining the distribution of domain sizes, but there is little evidence of how line tension affects membrane organization. We have investigated the effects of the line tension on the formation and stability of liquid ordered domains in model lipid bilayers with raft-like composition by means of time-lapse confocal microscopy coupled to atomic force microscopy. We varied the hydrophobic mismatch between the two phases, and consequently the line tension, by modifying the thickness of the disordered phase with phosphatidylcholines of different acyl chain length. The temperature of domain formation, the dynamics of domain growth, and the distribution of domain sizes depend strongly on the thickness difference between the domains and the surrounding membrane, which is related to line tension. When considering line tension calculated from a theoretical model, our results revealed a linear increase of the temperature of domain formation and domain growth rate with line tension. Domain budding was also shown to depend on height mismatch. Our experiments contribute significantly to our knowledge of the physical-chemical parameters that control membrane organization. Importantly, the general trends observed can be extended to cellular membranes.
目前，细胞膜的组织和功能原理尚未得到充分理解。筏假说表明细胞膜中存在结构域或筏，它们作为蛋白质和脂质平台发挥作用。它们在重要的细胞过程中具有功能作用，如蛋白质分选或细胞信号传导等。理论研究表明，结构域边缘的界面能，也称为线张力，是决定结构域大小分布的关键参数，但几乎没有证据表明线张力如何影响膜的组织。我们通过延时共聚焦显微镜与原子力显微镜相结合的方法，研究了线张力对具有筏状组成的模型脂质双层中液晶有序结构域形成和稳定性的影响。我们通过用不同酰基链长度的磷脂酰胆碱改变无序相的厚度，来改变两相之间的疏水错配，从而改变线张力。结构域形成的温度、结构域生长的动力学以及结构域大小的分布强烈依赖于结构域与周围膜之间的厚度差异，而这与线张力有关。当考虑从理论模型计算得到的线张力时，我们的结果表明结构域形成温度和结构域生长速率随线张力呈线性增加。结构域出芽也显示取决于高度错配。我们的实验对我们了解控制膜组织的物理化学参数有很大贡献。重要的是，观察到的一般趋势可以扩展到细胞膜。
