Fluid bilayer structure determination by the combined use of x-ray and neutron diffraction. I. Fluid bilayer models and the limits of resolution.
Fluid bilayer structure determination by the combined use of x-ray and neutron diffraction. I. Fluid bilayer models and the limits of resolution.
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DOI：
10.1016/s0006-3495(91)82208-1
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发表时间：
1991
影响因子：
3.4
通讯作者：
M. Wiener;S. White
中科院分区：
文献类型：
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作者：
M. Wiener;S. White
这是第一次在一系列的文件有关的方法，用于确定的结构的流体磷脂双层在液晶（L α）相。基本方法是准分子模型的联合改进（King和白色，1986年）。Biophys. J. 49：1047-1054）。我们在这里提出（a）准分子模型的基本原理，（B）热无序双层膜的分辨率问题的性质，和（c）的分辨率的分析实验中，高斯函数被用来描述亚分子组分的分布。我们表明，多层液晶双层最好描述的卷积一个完美的晶格功能与热无序的双层晶胞。在这样的系统上的层状衍射测量通常仅产生5-10级衍射数据，从该衍射数据可以构建单位晶胞的跨双层轮廓。这些跨双层分布的正则分辨率（定义为布拉格间距除以最高记录衍射级的指数）通常为5-10 A。使用简单的模型计算，我们表明，典型的分辨率是一个衡量的宽度的分布的成分的单位细胞，而不是一个衡量的空间分离的分布。宽度提供了双层成分的热运动的量度，其可以由高斯函数描述。基于典型的实验误差，可以以0.1- 0.5A的精度确定分布中心的平衡位置。
This is the first in a series of papers concerned with methods for the determination of the structures of fluid phospholipid bilayers in the liquid-crystalline (L alpha) phase. The basic approach is the joint refinement of quasimolecular models (King and White, 1986. Biophys. J. 49:1047–1054) using x-ray and neutron diffraction data. We present here (a) the rationale for quasimolecular models, (b) the nature of the resolution problem for thermally disordered bilayers, and (c) an analysis of the resolution of experiments in which Gaussian functions are used to describe the distribution of submolecular components. We show that multilamellar liquid-crystalline bilayers are best described by the convolution of a perfect lattice function with a thermally disordered bilayer unit cell. Lamellar diffraction measurements on such a system generally yield only 5–10 orders of diffraction data from which transbilayer profiles of the unit cell can be constructed. The canonical resolution of these transbilayer profiles, defined as the Bragg spacing divided by the index of the highest recorded diffraction order, is typically 5–10 A. Using simple model calculations, we show that the canonical resolution is a measure of the widths of the distributions of constituents of the unit cell rather than a measure of the spatial separation of the distributions. The widths provide a measure of the thermal motion of the bilayer constituents which can be described by Gaussian functions. The equilibrium positions of the centers of the distributions can be determined with a precision of 0.1–0.5 A based upon typical experimental errors.