Small‐angle Scattering of Neutrons and X‐rays

John YH Chow, University of Sydney, New South Wales, Australia
Jill Trewhella, University of Sydney, New South Wales, Australia

Published online: January 2010

DOI: 10.1002/9780470015902.a0003047.pub2

Small-angle scattering of X-rays and neutrons is used to study the structures of biological macromolecules in solution. Where the components of biomolecular complexes have different scattering densities, scattering data provide structural information on the individual components and their relative dispositions. One can therefore gain insights into protein–protein and protein–deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) interactions within functional complexes. Although scattering data are inherently low resolution and limited in information content due to the random orientations of the scattering molecules, recent applications that use data from complementary methods have facilitated the interpretation of scattering data in terms of detailed models. Advances in computational methods and user interfaces have enabled nonspecialists to use the technique to advance our understanding of biomolecular systems. The increasing availability of synchrotron facilities has also enabled advances in studies of time-dependent changes in protein structure and the development of high-throughput approaches.

Key concepts:

  • Small-angle scattering provides information on the shapes of biological macromolecules in solution.
  • Neutron contrast variation reveals the structures and disposition of the components within biomolecular complexes and assemblies.
  • Proteins and polynucleotides naturally have different scattering densities for X-rays and neutrons and can therefore be distinguished in a scattering experiment.
  • Protein deuteration combined with systematic variation in solvent detueration can provide enhanced contrast variation capability for protein complexes.
  • Small-angle solution scattering data complements the higher resolution structural data from crystallography and NMR.
  • Small-angle scattering improves solution structure determination by providing information on long-range distances that complements the predominantly short-range distance information obtained by NMR.
  • Solution scattering data complements high-resolution crystallography by providing insights into conformational dynamics that are observed as a result of ligand binding or other changes in biological state.
  • Synchrotron X-ray sources enable time-resolved solution scattering experiments to probe conformational dynamics in proteins and DNA or RNA.
  • Structural characterization by small-angle scattering requires highly pure, monodisperse identical particles in solution.

Keywords: biomolecular complexes; protein structure; nucleic acid interactions; solution scattering; contrast variation

Figure 1. Calculated P(r) profiles for differently shaped scattering particles. In the case of the single-lobed objects, the P(r) functions for the sphere and prolate ellipsoid show how the asymmetry in P(r) increases as the object becomes more asymmetric. For the two-lobed objects, the P(r) functions are very sensitive to the relative dispositions of the two identically shaped lobes. The peak at the shorter r values is dominated by vector lengths within a single lobe, whereas the peak or shoulder at longer r values is dominated by vector lengths between the lobes.
Figure 2. Average scattering length densities for biological molecules as a function of the fraction of D2O in the solvent. The slope on the lines arises from the exchange of labile hydrogens.
Figure 3. (Left) X-ray and neutron scattering data for the KinA–Sda complex in which the Sda is deuterated. Each scattering profile is labelled to indicate that it is either X-ray data, or in the case of the neutron data, the percentage deuteration of the solvent. The data are in black and the model fits based on the model to the right are red lines. (Right) The atomic model of KinA–Sda that was optimized against the scattering data. The colour scheme indicates the fact that KinA (cyan) is a dimer (monomers coloured light and dark) that binds two Sda molecules (orange and yellow). KinA is an auto-kinase that phosphorylates a histidine, coloured red, on the KinA dimerization domains.
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    Svergun DI and Koch MH (2003) Small-angle scattering studies of biological macromolecules in solution. Reports on Progress in Physics 66: 1735–1782.
    Whitten AE and Trewhella J (2009) Small-angle scattering and neutron contrast variation for studying bio-molecular complexes. Methods in Molecular Biology (Clifton, NJ) 544: 307–323.

Related Sub-Topics:

X-Ray Crystallography | Biochemical and Biophysical Techniques | Biomolecular Interactions
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Article Title: Small‐angle Scattering of Neutrons and X‐rays
 
How to Cite close
Chow, John YH, and Trewhella, Jill(Jan 2010) Small‐angle Scattering of Neutrons and X‐rays. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003047.pub2]