Analysis of intrinsically disordered proteins by small-angle X-ray scattering.

Small-angle scattering of X-rays (SAXS) is a method for the low-resolution structural characterization of biological macromolecules in solution. The technique is highly complementary to the high-resolution methods of X-ray crystallography and NMR. SAXS not only provides shapes, oligomeric state, and quaternary structures of folded proteins and protein complexes but also allows for the quantitative analysis of flexible systems. Here, major procedures are presented to characterize intrinsically disordered proteins (IDPs) using SAXS. The sample requirements for SAXS experiments on protein solutions are given and the sequence of steps in data collection and processing is described. The use of the recently developed advanced computational tools to quantitatively characterize solutions of IDPs is presented in detail. Typical experimental and potential problems encountered during the use of SAXS are discussed.