Likelihood-based estimation of substructure content from single-wavelength anomalous diffraction (SAD) intensity data.
Likelihood-based estimation of substructure content from single-wavelength anomalous diffraction (SAD) intensity data.
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DOI：
10.1107/s2059798321004538
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发表时间：
2021-07-01
期刊：
影响因子：
--
通讯作者：
Read RJ
中科院分区：
文献类型：
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作者：
Hatti KS;McCoy AJ;Read RJ
提出了一种基于强度的似然方法来估计来自异常子结构的散射，该方法考虑了Bijvoet对中测量误差的影响以及这些误差之间的相关性。当信噪比较低时，悲伤的相移可能是一项挑战。在这种情况下，对子结构含量的准确估计可以决定是否能够成功地确定异常散射体位置的子结构。这里，提出了一种基于似然的目标函数，直接根据测量的强度准确地估计反常散射贡献的强度，确定与Bijvoet对作为分辨率的函数相关的复数相关参数。这给出了一种新的测量内在异常信号的方法。SAD似然目标函数还考虑了Bijvoet Mate的强度测量中的相关误差，这可能是由于辐射损害的影响而引起的。当假设异常信号主要来自包括一个具有已知值f‘’的异常散射体的子结构，并且当晶体的蛋白质组成被正确估计时，可以在知道亚结构之前根据主要异常散射体的原子含量来解释精化的复数关联参数。在357例有有用异常信号的SAD病例的精选数据库上，对亚结构含量的最大似然估计进行了检验。子结构含量的先前估计与分阶段计算确定的含量高度相关，相关系数(在对数-对数基础上)为0.72。
An intensity-based likelihood method is provided to estimate scattering from an anomalous substructure considering the effect of measurement errors in Bijvoet pairs and the correlations between these errors. SAD phasing can be challenging when the signal-to-noise ratio is low. In such cases, having an accurate estimate of the substructure content can determine whether or not the substructure of anomalous scatterer positions can successfully be determined. Here, a likelihood-based target function is proposed to accurately estimate the strength of the anomalous scattering contribution directly from the measured intensities, determining a complex correlation parameter relating the Bijvoet mates as a function of resolution. This gives a novel measure of the intrinsic anomalous signal. The SAD likelihood target function also accounts for correlated errors in the measurement of intensities from Bijvoet mates, which can arise from the effects of radiation damage. When the anomalous signal is assumed to come primarily from a substructure comprising one anomalous scatterer with a known value of f′′ and when the protein composition of the crystal is estimated correctly, the refined complex correlation parameters can be interpreted in terms of the atomic content of the primary anomalous scatterer before the substructure is known. The maximum-likelihood estimation of substructure content was tested on a curated database of 357 SAD cases with useful anomalous signal. The prior estimates of substructure content are highly correlated to the content determined by phasing calculations, with a correlation coefficient (on a log–log basis) of 0.72.