The open-source Python program PDB2INS is designed to prepare a .ins file for refinement with SHELXL [Sheldrick (2015). Acta Cryst. C71, 3-8], taking atom coordinates and other information from a Protein Data Bank (PDB)-format file. If PDB2INS is provided with a four-character PDB code, both the PDB file and the accompanying mmCIF-format reflection data file (if available) are accessed via the internet from the PDB public archive [Read et al. (2011). Structure, 19, 1395-1412] or optionally from the PDB_REDO server [Joosten, Long, Murshudov & Perrakis (2014). IUCrJ, 1, 213-220]. The SHELX-format .ins (refinement instructions and atomic coordinates) and .hkl (reflection data) files can then be generated without further user intervention, appropriate restraints etc. being added automatically. PDB2INS was tested on the 23 974 X-ray structures deposited in the PDB between 2008 and 2018 that included reflection data to 1.7 Å or better resolution in a recognizable format. After creating the two input files for SHELXL without user intervention, ten cycles of conjugate-gradient least-squares refinement were performed. For 96% of these structures PDB2INS and SHELXL completed successfully without error messages.
Keywords: PDB format; SHELXL; crystal structure refinement; macromolecules.