Beyond 3 Å^-1: total X-ray scattering and atomic pair distribution function (PDF) analysis to determine the high-resolution structure of protein and polysaccharide in aqueous solutions

Resolving structures and dynamics of biomacromolecules in aqueous solutions at high spatial resolution are experimentally nontrivial due to the high instrumental requirements and challenges in modeling. Small-angle x-ray/neutron scattering, using scattering data below ≈ 1 Å^-1, provides low-resolution structural information of biomacromolecules. While there have been reports of wide-angle scattering characterization (up to ≈ 3 Å^-1) of biomacromolecules, high-quality data suitable for high-resolution modeling providing detailed insights into the structure are unavailable. Here, for the first time, by taking advantage of high-energy wide-angle X-ray scattering (WAXS) at 11-ID-B at the Advanced Photon Source, Argonne National Laboratory, we reliably collected WAXS profiles of several types of biomacromolecules including protein and polysaccharide in aqueous solutions up to ≈ 20 Å^-1. Our atomic pair distribution function analyses shed new light on resolving the conformation states of these biomacromolecules.