XChem explorer (XCE) was used for processing the X-ray diffraction data and PanDDA for model building. For molecular replacement the PaFabF C164Q structure with PDB ID 4JB6 was used as an input model. The ground model required for PanDDA was build using the best data sets not containing a ligand obtained when collecting diffraction data from the 25 crystals used for screening for soaking conditions as described above. Subsequently, this ground model was used in PanDDA to process the ligand-soaked datasets to increase the detection limit of weakly binding fragment. Coot was used for the visual inspection of the models and Refmac5 for refinement. Refined crystal structures were deposited in the Protein Data Bank with the PDB IDs 5SN5 -5SOH (Table ).