Driving Force for Water Permeation Across Lipid Membranes

The permeation of water across lipid membranes is of paramount importance in biological and technological processes. The driving force for such energetically unfavorable processes is explored here. To determine the effect of the lipid membrane conformation, water transport in both liquid-crystalline and ordered gel phases is studied in zwitterionic dipalmitoyl phosphatidylcholine (DPPC) bilayers and anionic 1,2-dilauroyl-sn-glycero-3-phosphol-l-serine (DLPS) bilayers via atomistic molecular dynamics simulations. These phases are accessed by changing the temperature in DPPC membranes and by additionally changing the valency of counterions (i.e., Na+ and Zn2+) in DLPS membranes. The membrane conformation is found to play a critical function in water permeation, regardless of the type of lipid. The fluctuations in the potential energy are found to have a significant, if not the exclusive, role in the transportation of water across lipid membranes.脂质膜介导的水渗透过程在生物学与技术应用领域均具有至关重要的意义。本文针对这类能量不利过程的驱动力展开探究。为明确脂质膜构象的影响，我们通过全原子分子动力学模拟（atomistic molecular dynamics simulations），分别在两性离子型二棕榈酰磷脂酰胆碱（dipalmitoyl phosphatidylcholine, DPPC）双分子层与阴离子型1,2-二月桂酰-sn-甘油-3-磷酸-L-丝氨酸（1,2-dilauroyl-sn-glycero-3-phospho-L-serine, DLPS）双分子层的液晶相与有序凝胶相中开展水传输特性研究。其中，DPPC膜的相态可通过调控温度实现切换，DLPS膜的相态则可通过改变抗衡离子（即Na⁺与Zn²⁺）的价态进行调控。研究发现，无论脂质类型如何，膜构象均对水渗透过程起到关键调控作用；势能涨落即便并非唯一影响因素，也对跨脂质膜的水传输过程具有显著贡献。