HullRadSAS is an algorithm for calculating the hydration and hydrodynamic properties of a macromolcule from a structure file.

HullRadSAS calculates the same hydrodynamic properties as the orginal HullRad with the addition of two types of macromolecular hydration and also calculates a hydrated radius of gyration for comparison to SAXS data. The original HullRad only gives you the anhydrous radius of gyration for comparison to SANS data.

The above images illustrate the two types of hydration calculated by HullRadSAS: First shell and entrained hydration.

• Left, the volume (cyan) between a solvent accessible surface (orange dots) and surface of the macromolecular atoms (gray spheres) represents the first hydration shell.
• Right, the volume (magenta) between the solvent accessible surface (orange dots) and convex hull (thick black lines) represents water entrained in crevices, grooves, and pockets of the molecule but part of the hydrodynamic volume.

Try it out - Download the code clicking on the link below.

• The HullRadSAS python script requires either, that your python has numpy and scipy, or the prior installation of qconvex, a program in the qhull suite of programs that implements the Quickhull algorithm for computing the convex hull.
  
• If you have numpy and scipy, you do NOT have to install qconvex from the qhull suite. Further instructions are in the header of the code.
• Read the instructions in the header of the code, especially the import statements. You may have to install some python libraries.
• Note that HullRadSAS only works for molecular types that may be parsed with biopython (Bio). This is because the biopython accessible surface library is used to construct the molecular surface dots.

• Version 1 (October, 2022)
  • The program as described in Fleming, Correia and Fleming, Eur. Biophys. J., 2023 (See Reference link above).
• Version 1.1 (December, 2022)
  • The rounded corners of the convex hull built on the SAS causes a slightly larger Dmax value compared to the original HullRad. This affected the axial ratio and therefore significantly affected the rotational diffusion properties. Fixed to agree with experimental values.
• Version 2.0 (July, 2023)
  • Addition of hydrated radius of gyration for comparison to SAXS data.
Version 3.0 (July, 2024)
• Addition of non-ideality properties.
Version 3.1 (Oct, 2024)
• Update nucleic acid partial specific volumes to agree with experimentally determined values.