Three-beam interference is a sensitive measure of the efficacy of macromolecular refinement techniques
Three-beam interference is a sensitive measure of the efficacy of macromolecular refinement techniques
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DOI：
10.1107/s0907444903015403
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发表时间：
2003-10-01
影响因子：
2.2
通讯作者：
Sweet, RM
中科院分区：
文献类型：
--
作者：
Soares, AS;Caspar, DLD;Sweet, RM
从胰岛素晶体记录的三重态相位用于测量模型细化期间相位的改善，并量化细化中每个步骤所做的贡献。使用1.54埃Cu Ka辐射从菱形猪胰岛素晶体记录常规振幅数据至1.5埃分辨率。初始原子模型和起始相位是从已发表的结构中获得的，并且原子模型针对使用CNS的振幅数据进行了改进。使用三光束干涉技术和1.1埃波长的同步加速器辐射从类似的晶体测量的800个三重态相进行了比较。溶剂区域进一步改善使用一种新的密度改性程序。计算的三重态相，从模型中得到的每个步骤后，在细化，并与记录的三重态相进行比较。记录的三重态相位和计算的三重态相位之间的平均差异被用作在细化中的每个阶段的模型的正确性的无偏测量。在每个细化步骤后，从三重相的差异估计平均单个相位误差。传统的原子细化近似的起始模型减少了平均个人的相位误差从21.6到14.7度。溶剂区的改进，包括差分图平坦化程序，将单个相位误差进一步降低了2.6度。对四种氨基酸的离散无序进行建模，额外改善了0.5度，最终个体相位误差为11.6度。
Triplet phases recorded from insulin crystals were used to measure the improvement of phases during model refinement and to quantify the contribution made by each step in the refinement. Conventional amplitude data were recorded to 1.5 Angstrom resolution from rhombohedral pig insulin crystals using 1.54 Angstrom Cu Kalpha radiation. An initial atomic model and starting phases were obtained from a published structure and the atomic model was refined against the amplitude data using CNS. The refined phases were compared with 800 triplet phases that were measured from similar crystals using a three-beam interference technique and 1.1 Angstrom wavelength synchrotron radiation. The solvent region was improved further using a novel density-modification procedure. Calculated triplet phases were obtained from the model after each step in the refinement and were compared with the recorded triplet phases. The average difference between the recorded triplet phases and the calculated triplet phases was used as an unbiased measure of the correctness of the model at each stage in the refinement. The average individual phase error was estimated from discrepancies from triplet phases after each refinement step. Conventional atomic refinement of an approximate starting model reduced the average individual phase error from 21.6 to 14.7degrees. Improvement of the solvent region, including the difference-map flattening procedure, reduced the individual phase error by a further 2.6degrees. Modeling the discrete disorder of four amino acids accounted for an additional 0.5degrees improvement and the final individual phase error was 11.6degrees.