A revised partiality model and post-refinement algorithm for X-ray free-electron laser data.
A revised partiality model and post-refinement algorithm for X-ray free-electron laser data.
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DOI：
10.1107/s1399004715006902
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发表时间：
2015-06
期刊：
影响因子：
--
通讯作者：
Stuart DI
中科院分区：
文献类型：
--
作者：
Ginn HM;Brewster AS;Hattne J;Evans G;Wagner A;Grimes JM;Sauter NK;Sutton G;Stuart DI
本文提出了一种适用于XFEL快拍衍射数据的修正后的修正模型和修正后的算法，并通过在1.3 μ m X射线波长处观测S原子的反常密度得到了证实。 利用X射线自由电子激光（XFEL）数据来解决使用实验定相方法（如硫单波长反常色散（SAD））的结构的研究一直受到FEL X射线衍射模型缺陷的阻碍。由于方向矩阵和过于简单的方向矩阵模型中的误差，研究人员需要大量的图像来收敛到结构因子振幅的可靠估计，这可能对所有生物系统都不可行。在这里，细胞质多角体病毒17型（CPV 17）在1.3 μ m波长的直线加速器相干光源（LCLS）收集的数据进行了重新审查。 先前公布的定义的自放大自发辐射（SASE）脉冲照射的反射的反射模型是建立在，它定义了一个分数0和1之间的交叉点的基础上的反射与扩展的埃瓦尔德球建模的超高斯波长分布的X射线束。提出了一种后细化的方法来细化该模型的参数。这已经从7225个图像数据集产生了具有3.15%至1.46 μ m分辨率的总体差异（通过计算R分裂值）的合并数据集。 结构中C、N和O原子的原子序数在电子密度图中是可区分的。在CPV 17的237个残基中有13个S原子，不包括初始无序的甲硫氨酸。这些只有0.42个异常散射电子，每个在1.3 nm波长，但12个具有单一的优势位置是很容易检测到的异常差异傅立叶映射。 人们希望，这些改进将导致XFEL实验相测定和结构测定的硫SAD，并将普遍增加实用的方法，为困难的情况下。
An updated partiality model and post-refinement algorithm for XFEL snapshot diffraction data is presented and confirmed by observing anomalous density for S atoms at an X-ray wavelength of 1.3 Å. Research towards using X-ray free-electron laser (XFEL) data to solve structures using experimental phasing methods such as sulfur single-wavelength anomalous dispersion (SAD) has been hampered by shortcomings in the diffraction models for X-ray diffraction from FELs. Owing to errors in the orientation matrix and overly simple partiality models, researchers have required large numbers of images to converge to reliable estimates for the structure-factor amplitudes, which may not be feasible for all biological systems. Here, data for cytoplasmic polyhedrosis virus type 17 (CPV17) collected at 1.3 Å wavelength at the Linac Coherent Light Source (LCLS) are revisited. A previously published definition of a partiality model for reflections illuminated by self-amplified spontaneous emission (SASE) pulses is built upon, which defines a fraction between 0 and 1 based on the intersection of a reflection with a spread of Ewald spheres modelled by a super-Gaussian wavelength distribution in the X-ray beam. A method of post-refinement to refine the parameters of this model is suggested. This has generated a merged data set with an overall discrepancy (by calculating the R split value) of 3.15% to 1.46 Å resolution from a 7225-image data set. The atomic numbers of C, N and O atoms in the structure are distinguishable in the electron-density map. There are 13 S atoms within the 237 residues of CPV17, excluding the initial disordered methionine. These only possess 0.42 anomalous scattering electrons each at 1.3 Å wavelength, but the 12 that have single predominant positions are easily detectable in the anomalous difference Fourier map. It is hoped that these improvements will lead towards XFEL experimental phase determination and structure determination by sulfur SAD and will generally increase the utility of the method for difficult cases.