From dilute to concentrated solutions of intrinsically disordered proteins: Sample preparation and data collection

It is well-known that an increasing proportion of proteins, protein regions, and partners of globular proteins are being recognized as having an intrinsic disorder, and therefore, not adopting a single three-dimensional structure in solution. For these proteins, small-angle X-ray scattering (SAXS) has become a premier method for examination, since it can provide information about the ensemble of the structural conformations as well as the intermolecular interactions. SAXS measurements can be performed from low to high protein concentrations under different physicochemical properties of the solution. The focus of this chapter is to introduce the basics of how to use SAXS for protein samples, for new and less experienced users, in a simple and concise manner, with emphasis on highly flexible proteins and regions. Methodological aspects in the sample preparation, experiment design, and data collection stages are raised that should be considered prior to attempting SAXS experiments. This is to ensure that high-quality SAXS data is obtained that enables accurate analysis. However, many of the points raised will also be worth considering for SAXS experiments of globular proteins.