title: Accurate assessment of mass, models and resolution by small-angle scattering.
abstract: 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.
authors.affiliation: Life Sciences Division, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA. rprambo@lbl.gov
authors.forename: Robert P
authors.initials: RP
authors.lastname: Rambo
authors.forename: John A
authors.initials: JA
authors.lastname: Tainer
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D008970:Molecular Weight; D018583:Pliability; D012367:RNA, Viral / Q000737:chemistry; D016601:RNA-Binding Proteins; D015203:Reproducibility of Results; D058928:Riboswitch / Q000235:genetics; D053838:Scattering, Small Angle; D012996:Solutions
chemical_list: D004268:DNA-Binding Proteins; C110410:RAD51AP1 protein, human; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D058928:Riboswitch; D012996:Solutions; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase