Single-wavelength anomalous diffraction

Single-wavelength anomalous diffraction (SAD) is a technique used in X-ray crystallography that facilitates the determination of the structure of proteins or other biological macromolecules by allowing the solution of the phase problem. In contrast to multi-wavelength anomalous diffraction (MAD), SAD uses a single dataset at a single appropriate wavelength.

Compared to MAD, SAD has weaker phasing power and requires density modification to resolve phase ambiguity. This downside is not as important as SAD's main advantage: the minimization of time spent in the beam by the crystal, thus reducing potential radiation damage to the molecule while collecting data. SAD also allows a wider choice of heavy atoms and can be conducted without a synchrotron beamline. Today, selenium-SAD is commonly used for experimental phasing due to the development of methods for selenomethionine incorporation into recombinant proteins.

SAD is sometimes called "single-wavelength anomalous dispersion", but no dispersive differences are used in this technique since the data are collected at a single wavelength.

• Multi-wavelength anomalous dispersion (MAD)
• Multiple isomorphous replacement (MIR)
• Anomalous scattering
• Anomalous X-ray scattering
• Patterson map

• W. A. Hendrickson (1985). "Analysis of Protein Structure from Diffraction Measurement at Multiple Wavelengths". Trans. ACA Vol 21.
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• J. Karle (1989). "Linear Algebraic Analyses of Structures with One Predominant Type of Anomalous Scatterer". Acta Crystallogr. A45, 303–307.
• A. Pahler, JL Smith & WA Hendrickson (1990). "A Probability Representation for Phase Information from Multiwavelength Anomalous Dispersion". Acta Crystallogr. A46, 537–540.
• T. C. Terwilliger (1994). "MAD Phasing: Bayesian Estimates of FA" Acta Crystallogr. D50, 11–16.
• T. C. Terwilliger (1994). "MAD Phasing: Treatment of Dispersive Differences as Isomorphous Replacement Information" Acta Crystallogr. D50, 17–23.
• R. Fourme, W. Shepard, R. Kahn, G l'Hermite & IL de La Sierra (1995). "The Multiwavelength Anomalous Solvent Contrast (MASC) Method in Macrocolecular Crystallography". J. Synchrotron Rad. 2, 36–48.
• E. de la Fortelle and G. Bricogne (1997) "Maximum-Likelihood Heavy-Atom Parameter Refinement for Multiple Isomorphous Replacement and Multiwavelength Anomalous Diffraction Methods". Methods in Enzymology 276, 472–494.
• W. A. Hendrickson and CM Ogata (1997) "Phase Determination from Multiwavelength Anomalous Diffraction Measurements". Methods in Enzymology 276, 494–523.
• J. Bella & M. G. Rossmann (1998). "A General Phasing Algorithm for Multiple MAD and MIR Data" Acta Crystallogr. D54, 159–174.
• J. M. Guss, E. A. Merritt, R. P. Phizackerley, B. Hedman, M. Murata, K. O. Hodgson, and H. C. Freeman (1989). "Phase determination by multiple-wavelength X-ray diffraction: crystal structure of a basic blue copper protein from cucumbers". Science 241, 806–811.
• B. Vijayakumar and D. Velmurugan (2013). "Use of europium ions for SAD phasing of lysozyme at the Cu Kα wavelength" Acta Crystallogr. F69, 20–24.
• J. P. Rose & B-C Wang (2016) "SAD phasing: History, current impact and future opportunities" Archives Biochem Biophys 602, 80-94.

• MAD phasing — an in depth tutorial with examples, illustrations, and references.

• The SSRL Absorption Package —Brennan S, Cowan PL (1992). "A suite of programs for calculating x-ray absorption, reflection and diffraction performance for a variety of materials at arbitrary wavelengths". Rev. Sci. Instrum. 63 (1): 850. Bibcode:1992RScI...63..850B. doi:10.1063/1.1142625.
• CHOOCH —Evans G, Pettifer RF (2001). "CHOOCH: a program for deriving anomalous-scattering factors from X-ray fluorescence spectra". J. Appl. Crystallogr. 34 (1): 82–86. doi:10.1107/S0021889800014655.
• Shake-and-Bake (SnB) —Smith GD, Nagar B, Rini JM, Hauptman HA, Blessing RH (1998). "The use of Snb to determine an anomalous scattering substructure". Acta Crystallogr D. 54 (Pt 5): 799–804. Bibcode:1998AcCrD..54..799S. doi:10.1107/S0907444997018805. PMID 9757093.
• SHELX —Sheldrick GM (1998). "SHELX: applications to macromolecules". In S Fortier (ed.). Direct methods for solving macromolecular structures. Dordrecht: Kluwer Academic Publishers. pp. 401–411. ISBN 0-7923-4949-0.{{cite book}}: CS1 maint: publisher location (link)

• Evans, Gwyndaf (October 1994). "The method of Multiple wavelength Anomalous Diffraction using Synchrotron Radiation at optimal X-ray energies: Application to Protein Crystallography". PhD Thesis. University of Warwick.