Sibyls: Structurally-Integrated Biology for Life Sciences

Integration of SAXS at SIBYLS

Small angle X-ray scattering provides rapid, conformational analysis of macromolecules in solution. In solution scattering, the signal from all orientations of the target molecules, relative to one another and the experimental apparatus, are averaged together. Solution scattering is continuous and radially symmetric (isotropic). As a solution technique, SAXS offers the potential for obtaining some information with every sample, does not require crystals or large amounts of material, and is a natural technique for understanding systems possessing substantial flexibility. SAXS can characterize shape and conformation in solution for quite small to very large macromolecular systems, so it avoids the size limitations. In addition, information derived from SAXS data can be useful both prior to and after high resolution structures are solved. The information content in scattering curves is substantially less than that in crystallography, which is an inherent limitation of this technique. However, SAXS information can be used to define low-resolution ab initio envelopes. Moreover, SAXS is not only likely to be more powerful in conjunction with atomic resolution structures but is also able in such combinations to provide more accurate and complete models of protein, RNA, and DNA structures, conformations, interactions, and assemblies in solution. The accessible experimental resolution can thus be made appropriate to the biological question being asked with SAXS measurements directly defining global shape and conformation in solution, whereas the combination of SAXS with computation plus high-resolution component structures provides more detailed three-dimensional information.