Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland.
MacCHESS, Cornell University, Ithaca, New York, USA.
Acta Crystallogr D Struct Biol. 2019 Mar 1;75(Pt 3):262-271. doi: 10.1107/S2059798319003103. Epub 2019 Mar 12.
Native single-wavelength anomalous dispersion (SAD) is the most attractive de novo phasing method in macromolecular crystallography, as it directly utilizes intrinsic anomalous scattering from native crystals. However, the success of such an experiment depends on accurate measurements of the reflection intensities and therefore on careful data-collection protocols. Here, the low-dose, multiple-orientation data-collection protocol for native SAD phasing developed at beamline X06DA (PXIII) at the Swiss Light Source is reviewed, and its usage over the last four years on conventional crystals (>50 µm) is reported. Being experimentally very simple and fast, this method has gained popularity and has delivered 45 de novo structures to date (13 of which have been published). Native SAD is currently the primary choice for experimental phasing among X06DA users. The method can address challenging cases: here, native SAD phasing performed on a streptavidin-biotin crystal with P2 symmetry and a low Bijvoet ratio of 0.6% is highlighted. The use of intrinsic anomalous signals as sequence markers for model building and the assignment of ions is also briefly described.
天然单波长反常散射（SAD）是大分子晶体学中最具吸引力的从头相位分析方法，因为它直接利用天然晶体的固有反常散射。然而，此类实验的成功取决于对反射强度的精确测量，因此需要仔细制定数据采集方案。本文回顾了瑞士光源 X06DA（PXIII）光束线开发的天然 SAD 相位分析的低剂量、多方向数据采集方案，并报告了过去四年在常规晶体（>50 µm）上的使用情况。由于该方法在实验上非常简单和快速，因此已广受欢迎，迄今为止已提供了 45 个从头结构（其中 13 个已发表）。目前，天然 SAD 是 X06DA 用户进行实验相位分析的首选方法。该方法可用于解决具有挑战性的情况：本文重点介绍了 P2 对称的链霉亲和素-生物素晶体和低 Bijvoet 比（0.6%）的天然 SAD 相位分析。还简要描述了将固有反常信号用作模型构建和离子分配的序列标记的用途。
