Current limits on determination of protonation state using neutron macromolecular crystallography

Neutron diffraction is a technique used to locate hydrogen and and deuterium atoms at medium data resolution in macromolecular structures. Typically, the structures are not determined de novo; instead, the structure has been previously determined with X-ray diffraction. The Protein Data Bank (PDB) was parsed to find homologue models for all neutron structures. The data table lists PDB IDs for X-ray structures that are similar to neutron models deposited in the PDB (as of October 2019). Methods The homologue protein sequences were obtained with the program BLAST. The X-ray model with the highest sequence identity and highest resolution (cut-offs: minimum sequence identity of 90% and minimum data resolution of 2Å) was considered as homologue. The BLAST search provided 156 homologues for all 161 neutron models.