Measuring the Interaction Radius of Proteins Using Small-Angle Scattering

Designing and measuring the interactions between proteins in solution is critical to formulating pharmaceutical drugs with key performance properties like low viscosity and phase stability. The structural characteristics of proteins, including their size, shape, and surface interactions, determine their solution structure. Herein, we introduce the theoretical basis for extracting the “interaction radius” information from SAXS or SANS data. This interaction radius reflects the range of interactions between proteins. We also demonstrate the practical application of this technique using experimental static SANS data from a model protein. We discuss the physical meaning of these results and the modifications required to use the method for proteins of different shapes (sphere, ellipsoid, etc.). This interaction parameter serves as an additional parameter for quantifying the interactions between proteins, in addition to the traditional second virial coefficient.