Department of Infectious Diseases, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands.
Acta Crystallogr D Struct Biol. 2023 Apr 1;79(Pt 4):339-344. doi: 10.1107/S2059798323001997. Epub 2023 Mar 28.
To determine a substructure from single-wavelength anomalous diffraction (SAD) data using Patterson or direct methods, the substructure-factor amplitude (|F|) is first estimated. Currently, the absolute value of the Bijvoet difference is widely used as an estimate of |F| values for SAD data. Here, an equation is derived from multivariate statistics and tested that takes into account the correlation between the observed positive (F) and negative (F) Friedel pairs and F along with measurement errors in the observed data. The multivariate estimation of |F| has been implemented in a new program, Afro. Results on over 180 test cases show that Afro provides a higher correlation to the final substructure-factor amplitudes (calculated from the refined, final substructures) than the Bijvoet differences and improves the robustness of direct-methods substructure detection.
利用 Patterson 或直接法从单波长反常散射（SAD）数据中确定亚结构时，首先要估计亚结构因子振幅（|F|）。目前，普遍采用 Bijvoet 差的绝对值作为 SAD 数据中 |F| 值的估计值。在此，从多元统计学中推导出一个考虑到观察到的正（F）和负（F）对映体以及 F 之间相关性以及观测数据中测量误差的方程。该 |F| 的多元估计已在一个名为 Afro 的新程序中实现。对超过 180 个测试案例的结果表明，与 Bijvoet 差值相比，Afro 与最终亚结构因子振幅（从精炼后的最终亚结构计算得出）的相关性更高，并提高了直接法亚结构检测的稳健性。
