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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >Direct phase selection of initial phases from single-wavelength anomalous dispersion (SAD) for the improvement of electron density and ab initio structure determination
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Direct phase selection of initial phases from single-wavelength anomalous dispersion (SAD) for the improvement of electron density and ab initio structure determination

机译：直接阶段选择的初始阶段单波长反常色散(SAD)电子密度的提高,从头开始结构测定

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摘要

Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (phi(1) and phi(2)) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the theta(DS) list as a criterion to select optimized phases phi('a)m from phi(1) or phi(2) of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases phi(SAD) has been developed. Based on this work, reflections with an angle theta(DS) in the range 35-145 degrees are selected for an optimized improvement, where theta(DS) is the angle between the initial phase phi(SAD) and a preliminary density-modification (DM) phase phi(NHL)(DM). The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.
机译：优化初始定相是一个随后成功的决定性因素电子密度修改、模型构建和结构测定的生物使用单波长大分子反常色散(SAD)的方法。阶段的解决方案(φφ(1)和(2))生成的在哈克从两个对称三角形阶段悲伤的方法事业的建设相位模糊。选相方法利用θ(DS)列表中作为标准来选择优化的阶段φ(一)mφφ(1)或(2)的一个子集反射的比例高的正确阶段来代替相应的最初的悲伤阶段φ(SAD)。工作,反思与一个角θ(DS)35 - 145度的选择范围优化改进,θ(DS)的地方夹角φ(SAD)和一个初始的阶段初步density-modification (DM)阶段φ(NHL) (DM)。额外的选相直接步骤之前简单的溶剂压扁无相使用现有的DM项目组合,如解决或从CCP4 DM,极大地提高了最后阶段的增加电子密度图的相关系数和减少意味着阶段错误。从直接提高阶段和密度地图选相方法的完整性残留的蛋白质分子与主要建造链和侧链是有效的增强结构的决心。

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