Small-angle neutron scattering (SANS) is a powerful technique for probing biomolecular structure, particularly through contrast matching, which masks the scattering of specific components. This is achieved by introducing deuterium into the solute or solvent to match their scattering length densities. Thus, if the solute has exchangeable hydrogens, hydrogen-deuterium exchange (HDX) between solute and solvent occurs. For proteins, the hydrogens which are exchanged depend on the structure and dynamics of the protein itself. Most SANS calculators treat the solute dependent contrast as a uniform distribution through the volume of the solute, thus potentially limiting accuracy. Additionally, the hydration shell contributes to the scattering and can shift the radius of gyration by up to 0.5 Å, depending on the contrast. The balance between structure-based HDX contributions and the hydration shell in calculations of SANS profiles from proteins remains underexplored. In this study, we used contrast variation and Stuhrmann analysis to distinguish their separate contributions to the calculated scattering profiles of several standard proteins published in the SASBDB. In our study, we demonstrate that both HDX and hydration shell effects are discernible via Stuhrmann analysis, enabling more accurate scattering profile calculations and improved interpretation of biomolecular structures in solution.
Hicks et al. (Sun,) studied this question.