Protein structure and dynamics can be probed using x-ray crystallography. Whereas the Bragg peaks are only sensitive to the average unit-cell electron density, the signal between the Bragg peaks—diffuse scattering—is sensitive to spatial correlations in electron-density variations. Although diffuse scattering contains valuable information about protein dynamics, the diffuse signal is more difficult to isolate from the background compared to the Bragg signal, and the reproducibility of diffuse signal is not yet well understood. We present a systematic study of the reproducibility of diffuse scattering from isocyanide hydratase in three different protein forms. Both replicate diffuse datasets and datasets obtained from different mutants were similar in pairwise comparisons (Pearson correlation coefficient ≥0.8). The data were processed in a manner inspired by previously published methods using custom software with modular design, enabling us to perform an analysis of various data processing choices to determine how to obtain the highest quality data as assessed using unbiased measures of symmetry and reproducibility. The diffuse data were then used to characterize atomic mobility using a liquid-like motions (LLM) model. This characterization was able to discriminate between distinct anisotropic atomic displacement parameter (ADP) models arising from different anisotropic scaling choices that agreed comparably with the Bragg data. Our results emphasize the importance of data reproducibility as a model-free measure of diffuse data quality, illustrate the ability of LLM analysis of diffuse scattering to select among alternative ADP models, and offer insights into the design of successful diffuse scattering experiments.

中文翻译：

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蛋白质 X 射线漫散射的再现性和模拟原子位移参数的潜在效用

可以使用 X 射线晶体学探测蛋白质结构和动力学。布拉格峰仅对平均晶胞电子密度敏感，而布拉格峰之间的信号（漫散射）对电子密度变化的空间相关性敏感。尽管漫散射包含有关蛋白质动力学的宝贵信息，但与布拉格信号相比，漫射信号更难从背景中分离出来，而且漫射信号的再现性尚不清楚。我们对三种不同蛋白质形式的异氰化物水合酶漫散射的再现性进行了系统研究。复制的扩散数据集和从不同突变体获得的数据集在成对比较中相似（Pearson 相关系数≥0.8）。数据的处理方式受到先前发布的方法的启发，使用具有模块化设计的定制软件，使我们能够对各种数据处理选择进行分析，以确定如何获得最高质量的数据，如使用对称性和可重复性的无偏测量评估。然后使用类似液体的运动 (LLM) 模型将漫射数据用于表征原子迁移率。这种表征能够区分由与布拉格数据相当一致的不同各向异性缩放选择产生的不同各向异性原子位移参数 (ADP) 模型。我们的结果强调了数据再现性作为漫反射数据质量的无模型度量的重要性，说明了漫散射的 LLM 分析在替代 ADP 模型中进行选择的能力，