Accurate assessment of mass, models and resolution by small-angle scattering

Nature. 2013 Apr 25;496(7446):477-81. doi: 10.1038/nature12070.


Modern small-angle scattering (SAS) experiments with X-rays or neutrons provide a comprehensive, resolution-limited observation of the thermodynamic state. However, methods for evaluating mass and validating SAS-based models and resolution have been inadequate. Here we define the volume of correlation, Vc, a SAS invariant derived from the scattered intensities that is specific to the structural state of the particle, but independent of concentration and the requirements of a compact, folded particle. We show that Vc defines a ratio, QR, that determines the molecular mass of proteins or RNA ranging from 10 to 1,000 kilodaltons. Furthermore, we propose a statistically robust method for assessing model-data agreements (χ(2)free) akin to cross-validation. Our approach prevents over-fitting of the SAS data and can be used with a newly defined metric, RSAS, for quantitative evaluation of resolution. Together, these metrics (Vc, QR, χ(2)free and RSAS) provide analytical tools for unbiased and accurate macromolecular structural characterizations in solution.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aldose-Ketose Isomerases / chemistry
  • DNA-Binding Proteins / chemistry
  • Models, Chemical
  • Models, Molecular*
  • Molecular Conformation
  • Molecular Weight
  • Pliability
  • RNA, Viral / chemistry
  • RNA-Binding Proteins
  • Reproducibility of Results
  • Riboswitch / genetics
  • Scattering, Small Angle*
  • Solutions


  • DNA-Binding Proteins
  • RAD51AP1 protein, human
  • RNA, Viral
  • RNA-Binding Proteins
  • Riboswitch
  • Solutions
  • Aldose-Ketose Isomerases
  • xylose isomerase