Noninvasive Structural Analysis of Intermediate Species During Fibrillation: An Application of Small-Angle X-Ray Scattering.

Structural investigation of intermediately formed oligomers and pre-fibrillar species is of tremendous importance in order to elucidate the structural principles of fibrillation, and because intermediate species have been suggested as the pathogenic agents in several amyloid diseases. Structural investigations are however greatly complicated by the dynamic changes between structural states of very different sizes and life-times. Small angle X-ray scattering (SAXS) is an ideal method to handle this challenge. The method provides information about the fibrillation process (number of species present and their volume fractions) and low-resolution 3-dimensional structural models of individual species, notably also of the intermediately formed, in-process species from undisturbed fibrillation equilibria. Here, we provide a detailed description of the methods used for the measurement and analysis of SAXS data from fibrillating samples, exemplified using data from our own research.