大分子晶体学中实验定相的成功主要取决于结合到目标晶体的重原子的准确位置。为了改进子结构确定的过程,已开发出一种基于宽松交替平均反射(RAAR)算法框架的改进相位恢复算法。重要的是,所提出的算法具有π半相位扰动的组合,用于弱反射,并强制使用基于直接方法的切线公式用于倒数空间中的强反射。所提出的算法在总共100个单波长异常衍射(SAD)实验数据集上得到了广泛的证明,包含不同质量的蛋白质和核酸结构。与标准RAAR算法相比,改进的相位恢复算法在SAD子结构确定中表现出显著提高的有效性和准确性,强调了额外约束对算法性能的重要性。此外,由于输入参数的自适应特性,在大多数情况下,所提出的算法可以在没有人工干预的情况下执行。从而便于集成到结构确定管道中。结合IPCAS软件套件,我们通过实验证明,在我们提出的算法的基础上,自动从头结构确定是可能的。
The success of experimental phasing in macromolecular crystallography relies primarily on the accurate locations of heavy atoms bound to the target crystal. To improve the process of substructure determination, a modified phase-retrieval algorithm built on the framework of the relaxed alternating averaged reflection (RAAR) algorithm has been developed. Importantly, the proposed algorithm features a combination of the π-half phase perturbation for weak reflections and enforces the direct-method-based tangent formula for strong reflections in reciprocal space. The proposed algorithm is extensively demonstrated on a total of 100 single-wavelength anomalous diffraction (SAD) experimental datasets, comprising both protein and nucleic acid structures of different qualities. Compared with the standard RAAR algorithm, the modified phase-retrieval algorithm exhibits significantly improved effectiveness and accuracy in SAD substructure determination, highlighting the importance of additional constraints for algorithmic performance. Furthermore, the proposed algorithm can be performed without human intervention under most conditions owing to the self-adaptive property of the input parameters, thus making it convenient to be integrated into the structural determination pipeline. In conjunction with the IPCAS software suite, we demonstrated experimentally that automatic de novo structure determination is possible on the basis of our proposed algorithm.