Chemin du Musée 10, Department of Biology, University of Fribourg, 1700 Fribourg, Switzerland.
J Phys Chem B. 2020 Sep 24;124(38):8278-8286. doi: 10.1021/acs.jpcb.0c03145. Epub 2020 Sep 11.
Lipid membranes are indispensable to life, and they regulate countless cellular processes. To investigate the properties of membranes under controlled conditions, numerous reconstitution methods have been developed over the last few decades. Several of these methods result in the formation of lipid bilayers containing residual hydrophobic molecules between the two monolayers. These contaminants might alter membrane properties, including bilayer thickness, that is usually inferred from measurements of membrane capacitance assuming a simple slab model. However, recent measurements on solvent-free bilayers raised significant questions on the reliability of this approach. To reconcile the observed discrepancies, we developed a protocol to predict membrane capacitance from the dielectric profile of lipid bilayers computed from molecular dynamics simulations. Our methodology shows excellent agreement against available data on solvent-free noncharged bilayers, and it confirms that the uniform slab model is a reliable approximation from which to infer membrane capacitance. We find that the effective electrical thickness contributing to membrane capacitance is different from the hydrophobic thickness inferred from X-ray scattering form factors. We apply our model to estimate the concentration of residual solvent in reconstituted systems, and we propose that our protocol could be used to infer membrane properties in the presence of hydrophobic solvents.
脂质膜对于生命是不可或缺的，它们调节着无数的细胞过程。为了在受控条件下研究膜的性质，过去几十年来已经开发出了许多重组方法。其中有几种方法会导致在两层单层之间形成含有残留疏水分子的脂质双层。这些污染物可能会改变膜的性质，包括双层厚度，这通常是通过假设简单的平板模型来测量膜电容来推断的。然而，最近对无溶剂双层的测量对这种方法的可靠性提出了重大质疑。为了解决观察到的差异，我们开发了一种从分子动力学模拟计算的脂质双层介电特性预测膜电容的方案。我们的方法与无溶剂非带电双层的可用数据非常吻合，并且证实了均匀平板模型是一种可靠的近似，可以从中推断膜电容。我们发现，对膜电容有贡献的有效电学厚度与从 X 射线散射因子推断出的疏水性厚度不同。我们将我们的模型应用于估计重组系统中残留溶剂的浓度，并提出我们的方案可用于在存在疏溶剂的情况下推断膜的性质。
