The Statistical Conformation of a Highly Flexible Protein: Small-Angle X-Ray Scattering of S. aureus Protein A

• Published in: Structure (London) 2014-08, Vol.22 (8), p.1184-1195
• Main Authors: Capp, Jo A., Hagarman, Andrew, Richardson, David C., Oas, Terrence G.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Binding; Mathematical analysis; Mathematical models; Models, Molecular; Molecular Biology - methods; Molecular Sequence Data; Polymer physics; Protein A; Protein Conformation; Proteins; SAXS; Scattering functions; Scattering, Small Angle; Staphylococcal Protein A - chemistry; Staphylococcus aureus - chemistry
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2014.06.011

Staphylococcal protein A (SpA) is a multidomain protein consisting of five globular IgG binding domains separated by a conserved six- to nine-residue flexible linker. We collected SAXS data on the N-terminal protein-binding half of SpA (SpA-N) and constructs consisting of one to five domain modules in order to determine statistical conformation of this important S. aureus virulence factor. We fit the SAXS data to a scattering function based on a new polymer physics model, which provides an analytical description of the SpA-N statistical conformation. We describe a protocol for systematically determining the appropriate level of modeling to fit a SAXS data set based on goodness of fit and whether the addition of parameters improves it. In the case of SpA-N, the analytical polymer physics description provides a depiction of the statistical conformation of a flexible protein that, while lacking atomistic detail, properly reflects the information content of the data. [Display omitted] •SAXS data for Staphylococcal protein A (SpA) are fit to a new polymer physics model•The best-fit model is minimally parameterized to match SAXS information content•SpA is a flexible protein that sweeps a 90 Å hemisphere on the cell surface•Protocol is proposed for matching model complexity to SAXS data information content Capp et al. describe a new approach for determining the conformational parameters of a flexible multidomain protein. Their polymer-physics-based analysis matches the information content of SAXS data and avoids overparameterization inherent in an ensemble-based approach.