Single-wavelength anomalous diffraction (SAD) is a technique used in
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
that facilitates the determination of the structure of
proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
or other biological macromolecules by allowing the solution of the
phase problem
In physics, the phase problem is the problem of loss of information concerning the phase that can occur when making a physical measurement. The name comes from the field of X-ray crystallography, where the phase problem has to be solved for the det ...
. In contrast to
multi-wavelength anomalous diffraction Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules ...
, SAD uses a single dataset at a single appropriate wavelength. One advantage of the technique is the minimization of time spent in the beam by the crystal, thus reducing potential radiation damage to the molecule while collecting data. 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. Today, selenium-SAD is commonly used for experimental phasing due to the development of methods for
selenomethionine
Selenomethionine (SeMet) is a naturally occurring amino acid. The L-selenomethionine enantiomer is the main form of selenium found in Brazil nuts, cereal grains, soybeans, and grassland legumes, while ''Se''-methylselenocysteine, or its γ-gluta ...
incorporation into recombinant proteins.
See also
*
Multi-wavelength anomalous dispersion Multi-wavelength anomalous diffraction (sometimes Multi-wavelength anomalous dispersion; abbreviated MAD) is a technique used in X-ray crystallography that facilitates the determination of the three-dimensional structure of biological macromolecules ...
(MAD)
*
Multiple isomorphous replacement Multiple isomorphous replacement (MIR) is historically the most common approach to solving the phase problem in X-ray crystallography studies of proteins. For protein crystals this method is conducted by soaking the crystal of a sample to be analyz ...
(MIR)
*
Anomalous scattering Anomalous X-ray scattering (AXRS or XRAS) is a non-destructive determination technique within X-ray diffraction that makes use of the anomalous dispersion that occurs when a wavelength is selected that is in the vicinity of an absorption edge of on ...
*
Anomalous X-ray scattering Anomalous X-ray scattering (AXRS or XRAS) is a non-destructive determination technique within X-ray diffraction that makes use of the anomalous dispersion that occurs when a wavelength is selected that is in the vicinity of an absorption edge of on ...
*
Patterson map The Patterson function is used to solve the phase problem in X-ray crystallography. It was introduced in 1935 by Arthur Lindo Patterson while he was a visiting researcher in the laboratory of Bertram Eugene Warren at MIT.
The Patterson function i ...
References
Further reading
*W. A. Hendrickson (1985). "Analysis of Protein Structure from Diffraction Measurement at Multiple Wavelengths". ''Trans. ACA'' Vol 21.
*J Karle (1980). "Some Developments in Anomalous Dispersion for the Structural Investigation of Macromolecular Systems in Biology". ''International Journal of Quantum Chemistry: Quantum Biology Symposium'' 7, 357–367.
*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.
External links
MAD phasing— an in depth tutorial with examples, illustrations, and references.
Computer programs
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—
''Shake-and-Bake''(''SnB'') —
SHELX—
Tutorials and examples
*{{cite web , title=The method of Multiple wavelength Anomalous Diffraction using Synchrotron Radiation at optimal X-ray energies: Application to Protein Crystallography , first=Gwyndaf , last=Evans , work=PhD Thesis , date=October 1994 , publisher=University of Warwick , url=http://www.gwyndafevans.co.uk/thesis-html/thesis.html
Crystallography