Bella J, Rossmann M G
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.
Acta Crystallogr D Biol Crystallogr. 1998 Mar 1;54(Pt 2):159-74. doi: 10.1107/s0907444997010469.
A phasing algorithm is presented for combining multiple wavelength anomalous dispersion (MAD) data from multiple types of anomalous scatterers, either in the same or in different derivative crystals, as well as for combining MAD data with multiple isomorphous replacement (MIR) data from different derivative crystals. A heavy-atom phasing and refinement program originally written by Rossmann [(1967) HATOMLSQ program, Purdue University, West Lafayette, Indiana, USA] has been modified to refine the parameters that define the anomalous and isomorphous scatterers and to determine protein phases by using all MAD and MIR derivatives simultaneously. The technique allows for appropriate weighting of every data set, including the native data, which contains neither an anomalous nor an isomorphous component. This method is a generalization of currently used heavy-atom methods. Numerical tests are presented for different experimental scenarios, including a double MAD experiment on the same crystal (diffraction data at two absorption edges), combination of two MAD experiments on different crystals, and combination of MAD data with MIR data from multiple crystals. An appendix shows how the Karle equations used in MAD phasing can be reformulated as a particular case of this algorithm.
本文提出了一种定相算法，用于组合来自多种类型反常散射体的多波长反常色散（MAD）数据，这些反常散射体可以在同一衍生晶体或不同衍生晶体中，同时也用于将MAD数据与来自不同衍生晶体的多同晶置换（MIR）数据进行组合。最初由罗斯曼编写的一个重原子定相和精修程序[（1967年）HATOMLSQ程序，美国印第安纳州西拉斐特普渡大学]已被修改，以精修定义反常散射体和同晶散射体的参数，并通过同时使用所有MAD和MIR衍生物来确定蛋白质相位。该技术允许对每个数据集进行适当加权，包括既不包含反常成分也不包含同晶成分的天然数据。此方法是当前使用的重原子方法的推广。针对不同实验场景给出了数值测试，包括对同一晶体的双MAD实验（在两个吸收边处的衍射数据）、不同晶体上的两个MAD实验的组合以及MAD数据与来自多个晶体的MIR数据的组合。附录展示了MAD定相中使用的卡尔勒方程如何可以重新表述为本算法的一个特殊情况。
