2012年09月01日 讯 /生物谷BIOON/ --生物膜像皮肤那样包围着细胞。它们也包围着在代谢和细胞分裂中发挥着重要功能的细胞器。科学家们长期以来在原理上就知道生物膜是如何被构建出来的，也知道水分子在维持相邻的膜之间最佳距离中发挥着作用。如今，在计算机模拟的帮助下，来自德国慕尼黑理工大学和柏林自由大学的研究人员发现两种不同的机制阻止相邻的膜表面粘附在一起。相关研究结果刊登在PNAS期刊上。
生物膜镶嵌有蛋白质和脂质。这些脂质都是双亲媒性分子，即它们都是由一个亲水的极性头部和一个疏水的非极性尾部组成。由于膜脂的这一结构特点，它们在水溶液中能自动聚拢形成脂双分子层。当两种膜的水溶性表面彼此靠近太近时，水合排斥(hydration repulsion)就产生，从而阻止膜表面接触。在两个完整的生物膜之间，它们总是存在只有几纳米厚的水薄层。但是，在此之前，科学家们不清楚水合排斥如何在分子水平上发挥作用。如今，研究人员详细地阐述了用来解释水合排斥的这两种不同机制的重要性。
在当前这项研究中，研究人员发现根据生物膜之间的距离，两种不同的机制发挥作用。如果生物膜之间相隔大约1纳米或更大的距离，那么水分子在阻止它们接近时发挥着决定性的作用。这时水分子发挥着类似缓冲器的作用，将生物膜推开。当这种距离相隔更短时，在相向的生物膜表面上的脂质相互抑制它们自己的移动，从而增加彼此之间的排斥力。(生物谷Bioon.com)
doi: 10.1073/pnas.1205811109
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Hydration repulsion between biomembranes results from an interplay of dehydration and depolarization
Emanuel Schnecka,b,1, Felix Sedlmeiera,b, and Roland R. Netz
Hydration repulsion dominates the interaction between polar surfaces in water at nanometer separations and ultimately prevents the sticking together of biological matter. Although confirmed by a multitude of experimental methods for various systems, its mechanism remained unclear. A simulation technique is introduced that yields accurate pressures between solvated surfaces at prescribed water chemical potential and is applied to a stack of phospholipid bilayers. Experimental pressure data are quantitatively reproduced and the simulations unveil a rich microscopic picture: Direct membrane–membrane interactions are attractive but overwhelmed by repulsive indirect water contributions. Below about 17 water molecules per lipid, this indirect repulsion is of an energetic nature and due to desorption of hydration water; for larger hydration it is entropic and suggested to involve water depolarization. This antagonistic nature and the presence of various compensating contributions indicate that the hydration repulsion is less universal than previously assumed and rather involves finely tuned surface-water interactions.
