Abstract
Small angle X-ray scattering (SAXS) is a well-known technique for analyzing the size and shape of proteins in solution. Standard SAXS uses data below about q = 0.25 Å⁻¹. Therefore, SAXS can only provide information regarding size changes in the target molecule, aggregation, and approximate molecular shape. On the other hand, X-ray scattering in the middle-angle region (q = 0.30–0.75 Å⁻¹) contains important information for analyzing molecular structure and conformational changes in solution, such as the distance between intramolecular tertiary structures and the distance between secondary structures. By using the data in this middle-angle region, we can visualize more detailed molecular behavior and conformational changes. The solution scattering method that includes this important middle-angle region information is named “middle angle X-ray scattering (MAXS)”. In this article, we introduce the “massive movement” of the structure of human kinase MAP2K4 in solution, which was revealed by structural ensemble analysis using MAXS.