Locating the anomalous scatterer substructures in halide and sulfur phasing.
Locating the anomalous scatterer substructures in halide and sulfur phasing.
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定位卤化物和硫相中的异常散射体子结构。
DOI：
10.1107/s090744490201884x
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
Sheldrick,GeorgeM
中科院分区：
文献类型：
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作者：
Uson,Isabel;Schmidt,Bernhard;vonBulow,Rixa;Grimme,Susanne;vonFigura,Kurt;Dauter,Miroslawa;Rajashankar,KanagalaghattaR;Dauter,Zbigniew;Sheldrick,GeorgeM
现在，数据质量的提高使得利用仅源自蛋白质固有的硫或特别是通过浸泡掺入的卤化物离子的微弱异常信号成为可能。后一种技术需要定位大量部分占据的卤化物位点。这个数字似乎与暴露的蛋白质表面大致成正比。本文探讨了程序 SHELXD 中实现的双空间从头计算方法在 SAD 实验中定位硫、SAD 和 MAD 实验中溴化物以及使用 SAD 和 SIRAS 确定异常原子子结构的碘化物亚结构的应用。生成与 Patterson 函数一致的原子集，作为 SHELXD 中双空间回收过程的起点。然后，通过使用 SHARP 的最大似然定相和使用程序 DM 进行密度修改，将子结构扩展为完整结构。子结构定位和后续定相的成功关键取决于数据的质量和异常信号的程度。这因每个晶体和浸泡而异，但对于相同的晶体，异常信号的显着性被发现对强度测量的冗余高度敏感，这在某些情况下造成了所有的差异。通过测定人 6-磷酸甘露糖/胰岛素样生长因子 II 受体（Man6P/IGFII 受体）的重复 11 的先前未知的结构（Man6P/IGFII 受体）来说明这一点，该结构的不对称单元中有 310 个氨基酸，通过将晶体浸泡在含有卤化物阴离子的冷冻保护剂溶液中来定相。
Improved data quality now makes it feasible to exploit the weak anomalous signal derived only from the sulfurs inherent to the protein or in particular from halide ions incorporated by soaking. The latter technique requires the location of a high number of partially occupied halide sites. This number appears to be roughly proportional to the exposed protein surface. This paper explores the application of dual-space ab initio methods as implemented in the program SHELXD to the location of substructures of sulfur in SAD experiments, bromide in SAD and MAD experiments and iodide using SAD and SIRAS to determine the anomalous-atom substructure. Sets of atoms consistent with the Patterson function were generated as a starting point for the dual-space recycling procedure in SHELXD. The substructure is then expanded to the full structure by maximum-likelihood phasing with SHARP and density modification with the program DM. Success in the location of the substructures and subsequent phasing depends critically on the quality of the data and on the extent of the anomalous signal. This varies with each crystal and soak, but for the same crystal the significance of the anomalous signal was found to be highly sensitive to the redundancy of the intensity measurements, which in some cases made all the difference. This is illustrated by the determination of the previously unknown structure of repeat 11 of the human mannose-6-phosphate/insulin-like growth factor II receptor (Man6P/IGFII-receptor), with 310 amino acids in the asymmetric unit, which was phased by soaking the crystals in a cryoprotectant solution containing halide anions.