Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, USA; Department of Physics and Astronomy, University of Delaware, Newark, DE, USA.
Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, USA.
Chem Phys Lipids. 2020 Nov;233:104983. doi: 10.1016/j.chemphyslip.2020.104983. Epub 2020 Oct 6.
This paper develops a framework to compute the small-angle neutron scattering (SANS) from highly curved, dynamically fluctuating, and potentially inhomogeneous membranes. This method is needed to compute the scattering from nanometer-scale membrane domains that couple to curvature, as predicted by molecular modeling. The detailed neutron scattering length density of a small planar bilayer patch is readily available via molecular dynamics simulation. A mathematical, mechanical transformation of the planar scattering length density is developed to predict the scattering from curved bilayers. By simulating a fluctuating, curved, surface-continuum model, long time- and length-scales can be reached while, with the aid of the planar-to-curved transformation, the molecular features of the scattering length density can be retained. A test case for the method is developed by constructing a coarse-grained lipid vesicle following a protocol designed to relieve both the osmotic stress inside the vesicle and the lipid-number stress between the leaflets. A question was whether the hybrid model would be able to replicate the scattering from the highly deformed inner and outer leaflets of the small vesicle. Matching the scattering of the full (molecular vesicle) and hybrid (continuum vesicle) models indicated that the inner and outer leaflets of the full vesicle were expanded laterally, consistent with previous simulations of the Martini forcefield that showed thinning in small vesicles. The vesicle structure is inconsistent with a zero-tension leaflet deformed by a single set of elastic parameters, and the results show that this is evident in the scattering. The method can be applied to translate observations of any molecular model's neutron scattering length densities from small patches to large length and timescales.
本文开发了一个框架，用于计算高度弯曲、动态波动且可能不均匀的膜的小角中子散射（SANS）。需要这种方法来计算与曲率耦合的纳米级膜域的散射，这是分子建模所预测的。小平面双层斑块的详细中子散射长度密度可以通过分子动力学模拟轻松获得。开发了一种数学、机械变换，将平面散射长度密度转换为弯曲双层的散射。通过模拟波动、弯曲、表面连续体模型，可以达到长时标和长标度，同时借助平面到弯曲的转换，可以保留散射长度密度的分子特征。通过构建一个粗粒脂质囊泡，按照设计来缓解囊泡内部的渗透压和双层之间的脂质数量压力的方案，开发了一个方法的测试案例。问题是杂交模型是否能够复制小囊泡高度变形的内、外层的散射。匹配完整（分子囊泡）和混合（连续体囊泡）模型的散射表明，完整囊泡的内、外层在横向扩张，这与先前显示小囊泡变薄的 Martini 力场模拟一致。囊泡结构与由单个弹性参数变形的零张力层片不一致，结果表明这在散射中是明显的。该方法可用于将任何分子模型的中子散射长度密度的观察结果从小斑块转换到大长度和时间尺度。
