Crystals were extracted from the capillary or fished directly from the drop, subject to cryoprotection by the equilibration with 15 % (v/v) glycerol prepared in the mother liquid, with or without 1 mM of the transition-state analogue (5)6-nitrobenzotriazole (ST), flash-cooled in liquid nitrogen and stored until data collection. Crystals were diffracted at the XALOC beamline of the Spanish synchrotron light radiation source (ALBA, Barcelona). Data were indexed and integrated with XDS and scaled with SCALA 70 of the CCP4 program suite. Molecular replacement was performed in Phaser, using the coordinates of GNCA4-WT (PDB ID: 5FQK ) as the search model. Refinement was initiated with the phenix.refine 73 module of the PHENIX suite, followed by manual building and water inspection in Coot. The final refinement of ligand coordinates, Bfactors and occupancies was achieved following several cycles of refinement including Titration-Libration-Screw (TLS) parameterization. The final model coordinates were verified with Molprobity. The resulting coordinates and the experimental structure factors have been deposited in the Protein Data Bank 77 (PDB IDs: 6TY6, 6TXD and 6TWW, for GNCA4-2, GNCA-12 and GNCA-19, respectively), and the corresponding crystallographic data statistics are provided in Table .