SAXS: A Versatile Biophysical Technique for Structural Study of Biological Macromolecules

The high popularity of Small Angle X-ray Scattering (SAXS) as reflected by the recent upsurge in the number of SAXS based publications is attributable to advances in high-brilliance synchrotron sources, detector technology, and also software analysis tools. While the data collection phase of a typical SAXS experiment is relatively simple, the data quality and interpretability is heavily dependent on the monodispersity of the sample. Sample preparation is therefore often the most crucial and involved part of a successful SAXS experiment. However despite elaborate purification protocols employed to ensure optimal sample quality, limited shelf-lives of biological macromolecules due to a variety of biochemical reasons have engendered a wide-spread demand for a size-exclusion chromatography setup integrated in-line with the SAXS camera (SEC-SAXS) thus separating the sample from potential contaminants such as aggregates or breakdown products immediately before exposure to x-rays, a technique pioneered at BioCAT. The default data collection strategy for a majority of SAXS experiments at BioCAT is now SEC-SAXS and this has considerably expanded the scope of SAXS at BioCAT as high quality scattering data can be extracted even from samples usually considered too unstable or polydisperse. In addition to a description of the SAXS setup at BioCAT, a few examples of projects that have benefited from it will be discussed.