SASpy: a PyMOL plugin for manipulation and refinement of hybrid models against small angle X-ray scattering data.

UNLABELLED: Complex formation and conformational transitions of biological macromolecules in solution can be effectively studied using the information about overall shape and size provided by small angle X-ray scattering (SAXS). Hybrid modeling is often applied to integrate high-resolution models into SAXS data analysis. To facilitate this task, we present SASpy, a PyMOL plugin that provides an easy-to-use graphical interface for SAXS-based hybrid modeling. Through a few mouse clicks in SASpy, low-resolution models can be superimposed to high-resolution structures, theoretical scattering profiles and fits can be calculated and displayed on-the-fly. Mouse-based manual rearrangements of complexes are conveniently applied to rapidly check and interactively refine tentative models. Interfaces to automated rigid-body and flexible refinement of macromolecular models against the experimental SAXS data are provided. AVAILABILITY AND IMPLEMENTATION: SASpy is available as open source at: github.com/emblsaxs/saspy/. Working installations of both PyMOL (www.pymol.org) and ATSAS (www.embl-hamburg.de/biosaxs/download.html) are required. CONTACT: apanjkovich@embl-hamburg.de or svergun@embl-hamburg.de.