Laboratory of Physics, Tampere University of Technology , 33101 Tampere, Finland.
J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8, Czech Republic.
Langmuir. 2018 Feb 20;34(7):2565-2572. doi: 10.1021/acs.langmuir.7b02855. Epub 2017 Oct 10.
Lung surfactant and a tear film lipid layer are examples of biologically relevant macromolecular structures found at the air-water interface. Because of their complexity, they are often studied in terms of simplified lipid layers, the simplest example being a Langmuir monolayer. Given the profound biological significance of these lipid assemblies, there is a need to understand their structure and dynamics on the nanoscale, yet there are not many techniques able to provide this information. Atomistic molecular dynamics simulations would be a tool fit for this purpose; however, the simulation models suggested until now have been qualitative instead of quantitative. This limitation has mainly stemmed from the challenge to correctly describe the surface tension of water with simulation parameters compatible with other biomolecules. In this work, we show that this limitation can be overcome by using the recently introduced four-point OPC water model, whose surface tension for water is demonstrated to be quantitatively consistent with experimental data and which is also shown to be compatible with the commonly employed lipid models. We further establish that the approach of combining the OPC four-point water model with the CHARMM36 lipid force field provides nearly quantitative agreement with experiments for the surface pressure-area isotherm for POPC and DPPC monolayers, also including the experimentally observed phase coexistence in a DPPC monolayer. The simulation models reported in this work pave the way for nearly quantitative atomistic studies of lipid-rich biological structures at air-water interfaces.
肺表面活性剂和泪液脂质层是在气-液界面处发现的具有生物学相关性的大分子结构的例子。由于它们的复杂性，通常根据简化的脂质层来研究它们，最简单的例子是 Langmuir 单层。鉴于这些脂质组装体具有深远的生物学意义，需要了解它们在纳米尺度上的结构和动力学，但能够提供这些信息的技术并不多。原子分子动力学模拟将是一种适合此目的的工具；然而，直到现在提出的模拟模型都是定性的，而不是定量的。这种限制主要源于正确描述与其他生物分子兼容的模拟参数的水表面张力的挑战。在这项工作中，我们表明，通过使用最近引入的四点 OPC 水模型，可以克服这一限制，该模型的水表面张力被证明与实验数据具有定量一致性，并且还与常用的脂质模型兼容。我们进一步确定，将 OPC 四点水模型与 CHARMM36 脂质力场相结合的方法为 POPC 和 DPPC 单层的表面压力-面积等温线提供了几乎定量的实验一致性，还包括 DPPC 单层中观察到的实验相共存。本工作中报告的模拟模型为在气-液界面处富含脂质的生物结构的几乎定量原子研究铺平了道路。
