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Anomalous diffraction in crystallographic phase evaluation

Published online by Cambridge University Press:  11 April 2014

Wayne A. Hendrickson*
Affiliation:
Department of Biochemistry and Molecular Biophysics, and Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, USA New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA
*
* Author for correspondence: W. A. Hendrickson, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA. Tel.: 1 212 305 3456; Email: wayne@xtl.cumc.columbia.edu

Abstract

X-ray diffraction patterns from crystals of biological macromolecules contain sufficient information to define atomic structures, but atomic positions are inextricable without having electron-density images. Diffraction measurements provide amplitudes, but the computation of electron density also requires phases for the diffracted waves. The resonance phenomenon known as anomalous scattering offers a powerful solution to this phase problem. Exploiting scattering resonances from diverse elements, the methods of MAD (multiwavelength anomalous diffraction) and SAD (single-wavelength anomalous diffraction) now predominate for de novo determinations of atomic-level biological structures. This review describes the physical underpinnings of anomalous diffraction methods, the evolution of these methods to their current maturity, the elements, procedures and instrumentation used for effective implementation, and the realm of applications.

Information

Type
Review Article
Copyright
Copyright © Cambridge University Press 2014 

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