Asymmetry of lipid bilayers induced by monovalent salt: Atomistic molecular-dynamics study
Asymmetry of lipid bilayers induced by monovalent salt: Atomistic molecular-dynamics study
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DOI：
10.1063/1.1942489
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发表时间：
2005-06-22
影响因子：
4.4
通讯作者：
Gurtovenko, AA
中科院分区：
文献类型：
--
作者：
Gurtovenko, AA
盐离子与生物膜脂质组分之间的相互作用对膜的结构、稳定性和功能至关重要。已知电池内部和外部的水性缓冲液的特定离子组成显著不同。为了模拟这样的情况，我们进行原子分子动力学（MD）模拟的单组分磷脂酰胆碱脂质双层分离两个含水水库和不含NaCl盐。为了实现两个膜侧附近的电解质组成的差异，双双层设置（即，在模拟箱中的两个双层）。事实证明，单价盐，仅与一个小叶接触，诱导双层小叶在50 ns的MD模拟后的结构，静电和动力学性质的显著不对称性。钠离子结合到与盐接触的小叶的羰基区域导致形成“Na-脂质”复合物，并且相应地降低该小叶的脂质的流动性。反过来，有吸引力的相互作用的氯离子（主要位于水相接近的水-脂质界面）与胆碱脂质基团导致大量（更垂直）重新取向的postphatidylcholine头基的小叶毗邻盐。在头基取向的双分子层的两侧上的差异，再加上盐诱导的水偶极子的重新取向，导致一个显着的不对称的电荷密度分布和静电电位的双分子层构成的两个小叶。虽然发现双层的总电荷密度对盐的存在几乎不敏感，但两个双层小叶之间的电荷分布的轻微不对称导致两个水相之间约85 mV的非零电位差。因此，细胞中膜电位量级的跨膜电位可以在两个水性隔室之间没有离子电荷不平衡的情况下出现。(c)2005年美国物理学会。
Interactions between salt ions and lipid components of biological membranes are essential for the structure, stability, and functions of the membranes. The specific ionic composition of aqueous buffers inside and outside of the cell is known to differ considerably. To model such a situation we perform atomistic molecular-dynamics (MD) simulations of a single-component phosphatidylcholine lipid bilayer which separates two aqueous reservoirs with and without NaCl salt. To implement the difference in electrolyte composition near two membrane sides, a double bilayer setup (i.e., two bilayers in a simulation box) is employed. It turns out that monovalent salt, being in contact with one leaflet only, induces a pronounced asymmetry in the structural, electrostatic, and dynamical properties of bilayer leaflets after 50 ns of MD simulations. Binding of sodium ions to the carbonyl region of the leaflet which is in contact with salt results in the formation of "Na-lipids" complexes and, correspondingly, reduces mobility of lipids of this leaflet. In turn, attractive interactions of chloride ions (mainly located in the aqueous phase close to the water-lipid interface) with choline lipid groups lead to a substantial (more vertical) reorientation of postphatidylcholine headgroups of the leaflet adjoined to salt. The difference in headgroup orientation on two sides of a bilayer, being coupled with salt-induced reorientation of water dipoles, leads to a notable asymmetry in the charge-density profiles and electrostatic potentials of bilayer constitutes of the two leaflets. Although the overall charge density of the bilayer is found to be almost insensitive to the presence of salt, a slight asymmetry in the charge distribution between the two bilayer leaflets results in a nonzero potential difference of about 85 mV between the two water phases. Thus, a transmembrane potential of the order of the membrane potential in a cell can arise without ionic charge imbalance between two aqueous compartments. (c) 2005 American Institute of Physics.