Accurate SAXS profile computation and its assessment by contrast variation experiments

Area of Science:

• Structural biology
• Biophysics
• Computational biology

Background:

• Characterizing protein and assembly structures in solution is crucial for structural biology.
• Small-angle X-ray scattering (SAXS) provides low-resolution structural information in solution.
• Accurate and rapid computation of SAXS profiles from atomic models is essential for experimental data analysis.

Purpose of the Study:

• To develop a fast and accurate computational tool for calculating small-angle X-ray scattering (SAXS) profiles.
• To improve the assessment of structural models using SAXS data.
• To enable the analysis of complex and heterogeneous biological systems.

Main Methods:

• Developed Fast Open-source X-ray scattering (FoXS), a computational tool for SAXS profile calculation.
• FoXS explicitly computes interatomic distances and implicitly models the first hydration layer.
• Validated FoXS using contrast variation experiments and compared it with existing methods (CRYSOL, AquaSAXS, etc.) on various biomolecular structures.

Main Results:

• FoXS demonstrated superior accuracy and speed compared to existing SAXS profile computation methods.
• The hydration layer model in FoXS accurately represents density changes and correlates well with experimental data.
• FoXS successfully analyzed heterogeneous and flexible biological samples, including protein filaments and DNA complexes.

Conclusions:

• FoXS is a highly accurate and efficient tool for calculating SAXS profiles, aiding structural biology research.
• The software facilitates the evaluation of structural model quality and the analysis of complex biological assemblies.
• FoXS is widely adopted as a web server and integrated into various structure determination pipelines.