Liu Qun, Hendrickson Wayne A
Biology Department, Brookhaven National Laboratory, PO Box 5000, 50 Bell Ave, Building 463, Upton, NY, 11973, USA.
Department of Biochemistry and Molecular Biophysics, Columbia University, 202 Black Building, 650 West 168th Street, New York, NY, 10032, USA.
Methods Mol Biol. 2017;1607:377-399. doi: 10.1007/978-1-4939-7000-1_16.
The normal elastic X-ray scattering that depends only on electron density can be modulated by an "anomalous" component due to resonance between X-rays and electronic orbitals. Anomalous scattering thereby precisely identifies atomic species, since orbitals distinguish atomic elements, which enables the multi- and single-wavelength anomalous diffraction (MAD and SAD) methods. SAD now predominates in de novo structure determination of biological macromolecules, and we focus here on the prevailing SAD method. We describe the anomalous phasing theory and the periodic table of phasing elements that are available for SAD experiments, differentiating between those readily accessible for at-resonance experiments and those that can be effective away from an edge. We describe procedures for present-day SAD phasing experiments and we discuss optimization of anomalous signals for challenging applications. We also describe methods for using anomalous signals as molecular markers for tracing and element identification. Emerging developments and perspectives are discussed in brief.
仅取决于电子密度的正常弹性X射线散射可因X射线与电子轨道之间的共振而被“反常”成分调制。反常散射由此精确识别原子种类，因为轨道能区分原子元素，这使得多波长和单波长反常衍射（MAD和SAD）方法成为可能。目前，SAD在生物大分子的从头结构测定中占主导地位，我们在此聚焦于主流的SAD方法。我们描述了可用于SAD实验的反常相位理论和相位元素周期表，区分了那些在共振实验中易于获得的元素和那些在远离吸收边时仍有效的元素。我们描述了当今SAD相位实验的程序，并讨论了针对具有挑战性的应用优化反常信号的方法。我们还描述了将反常信号用作分子标记进行追踪和元素识别的方法。简要讨论了新出现的进展和前景。
