α-Bungaratoxin structure revealed by a rapid method for averaging electron density of non-crystallographically translationally related molecules
α-Bungaratoxin structure revealed by a rapid method for averaging electron density of non-crystallographically translationally related molecules
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通过平均非晶体学平移相关分子的电子密度的快速方法揭示了 α-金环蛇毒素结构
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发表时间：
1980
期刊：
影响因子：
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通讯作者：
R. Stroud
中科院分区：
文献类型：
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作者：
D. Agard;R. Stroud
在大分子晶体学中，相同化学物质的多个独立图像经常出现在晶体不对称单元中。对于非晶体相关分子的密度平均是一种强大的技术，既可以改善密度图像，又可以进行后续的相细化。令人惊讶的是，非结晶对称轴往往与结晶对称轴平行。在这种情况下，平均电子密度图可以简单而直接地从观察到的结构因素中计算出来，而不需要在分子密度图中进行插值或平均。所描述的过程比在实空间域中用后续插值进行平均要有效得多。同样的算法可以反向使用，既可以非常快速地计算基于替换非晶体相关分子的“平均”密度图像的单位细胞的傅里叶变换Fc(s)，也可以直接用于基于最小化R = Σ ||Fo| - |Fc|| / Σ |Fo|的快速翻译函数搜索。这种残余比任何“帕特森”搜索技术更敏感，在分子间和分子内载体之间存在重叠。结合这些快速密度平均分析技术和随后从平均密度图中计算出的结构因子的计算，求解和细化了α-虫毒的晶体结构。快速翻译搜索和平均程序对α-虫毒结构的求解至关重要。
In macromolecular crystallography multiple and independent images of the same chemical species are often present in the crystallographic asymmetric unit. Averaging of density for non-crystallographically related molecules is a powerful technique both for improvement of the density image, and for subsequent phase refinement. Surprisingly often, a non-crystallographic axis of symmetry lies parallel to a crystallographic axis. In such cases, the averaged electron density map can be computed simply and directly from the observed structure factors without subsequent interpolation or averaging in the molecular density map. The procedure described is much more efficient than averaging with consequent interpolation in the real-space domain. The same algorithm can be used in reverse both for very rapid computation of the Fourier transform Fc(s) of a unit cell based on replacement of the 'averaged' density image for the non-crystallographically related molecules, and consequently for a rapid translation function search based on minimization of R = Σ ||Fo| - |Fc|| / Σ |Fo| directly. This residual is much more sensitive than any 'Patterson' search technique where there is overlap between inter- and intramolecular vectors. Jointly these rapid analytic techniques for density averaging and subsequent computation of calculated structure factors from the averaged density map were used to solve and refine the crystal structure of α-bungarotoxin. The rapid translation search and averaging procedures were crucial to the solution of the α-bungarotoxin structure which is described.