Using Small-angle X-ray Scattering to Characterize Biological Systems: A General Overview and Practical Tips.

Small-angle X-ray Scattering (SAXS) is a versatile and powerful technique with applications in a wide range of fields. The continuous improvements in hardware, data analysis software, and standards for validation significantly contributed to increase its popularity and, nowadays, SAXS is a well-established method. SAXS allows to study flexible and dynamic systems (e.g., proteins and other biomolecules) in solution, providing information about their size and shape. Contrary to other structural characterization methods, SAXS has no limitations on the size of the particle under study and can be used in integrated approaches to reveal important insights otherwise difficult to obtain regarding folding-unfolding, conformational changes, movement of flexible regions, and the formation of complexes.This chapter, in addition to a concise overview on the methodology, intends to systematically enumerate the main steps involved in sample preparation and data collection, processing and analysis including useful practical notes to identify and overcome common bottlenecks. This way, a less experienced user can use the content of the chapter as a starting point to properly design and perform a successful SAXS experiment.