Fluid bilayer structure determination by the combined use of x-ray and neutron diffraction. II. "Composition-space" refinement method.
Fluid bilayer structure determination by the combined use of x-ray and neutron diffraction. II. "Composition-space" refinement method.
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DOI：
10.1016/s0006-3495(91)82209-3
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发表时间：
1991
影响因子：
3.4
通讯作者：
Matthew C. Wiener;Sarah White
中科院分区：
文献类型：
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作者：
Matthew C. Wiener;Sarah White
这是描述利用x射线和中子衍射数据联合改进流体双层结构方法的两篇论文中的第二篇。我们在第一篇论文（Wiener， M. C. and S. H. White. 1990）中显示。Biophys。（J. 59:162-173），流体双层层通常由热无序的单元细胞组成的近乎完美的晶格，规范分辨率d/hmax是用简单高斯函数表示的准分子组分的宽度的量度。热失序使得“成分空间”表示成为可能，其中准分子高斯分布描述了每个组分的双分子层宽度上每单位长度占用的数量或概率。这种表示允许中子和x射线片层衍射数据的联合细化，通过一个准分子结构，同时适合两个衍射数据集。通过适当的中子或x射线散射长度对每个成分进行缩放，将成分空间剖面映射到适当的散射长度空间，以便与实验数据进行比较。其他广泛的性质，如质量，也可以通过适当缩放精制的组合物空间结构来获得。基于包含晶体和液晶结构信息的简单双分子层模型，我们估计具有hmax衍射阶数的流体双分子层将被具有大约hmax准分子组分的结构准确地表示。准分子组分的分配策略是通过对磷脂分子的详细解析来证明的，该解析是基于二肉豆酰磷脂酰胆碱晶体结构的一维投影。最后，我们详细讨论了组合空间联合细化所需的实验变量的数量。我们发现流体双层结构是由实验数据决定的。文中还讨论了在这种情况下特别重要的误差分析。
This is the second of two papers describing a method for the joint refinement of the structure of fluid bilayers using x-ray and neutron diffraction data. We showed in the first paper (Wiener, M. C., and S. H. White. 1990. Biophys. J. 59:162–173) that fluid bilayers generally consist of a nearly perfect lattice of thermally disordered unit cells and that the canonical resolution d/hmax is a measure of the widths of quasimolecular components represented by simple Gaussian functions. The thermal disorder makes possible a "composition space" representation in which the quasimolecular Gaussian distributions describe the number or probability of occupancy per unit length across the width of the bilayer of each component. This representation permits the joint refinement of neutron and x-ray lamellar diffraction data by means of a single quasimolecular structure that is fit simultaneously to both diffraction data sets. Scaling of each component by the appropriate neutron or x-ray scattering length maps the composition space profile to the appropriate scattering length space for comparison to experimental data. Other extensive properties, such as mass, can also be obtained by an appropriate scaling of the refined composition space structure. Based upon simple bilayer models involving crystal and liquid crystal structural information, we estimate that a fluid bilayer with hmax observed diffraction orders will be accurately represented by a structure with approximately hmax quasimolecular components. Strategies for assignment of quasimolecular components are demonstrated through detailed parsing of a phospholipid molecule based upon the one-dimensional projection of the crystal structure of dimyristoylphosphatidylcholine. Finally, we discuss in detail the number of experimental variables required for the composition space joint refinement. We find fluid bilayer structures to be marginally determined by the experimental data. The analysis of errors, which takes on particular importance under these circumstances, is also discussed.