Data collection, structure solution and refinement. X-ray crystallographic data were collected using synchrotron radiation at the Diamond Light Source (DLS, Didcot, United Kingdom) beamlines I04-1 and I03 equipped with a Dectris Pilatus 6M-F and a Pilatus3 6M detector, respectively. Reflections were integrated using MOSFLM and scaled with Scala (CCP4 suite). Data collection and processing statistics are reported in Table . The crystals of TbPTR1 and LmPTR1 belonged to the primitive monoclinic space group P21 and the primitive orthorhombic space group P212121, respectively. Both had a functional enzyme tetramer in the asymmetric unit. The structures were solved by molecular replacement using MOLREP and either a TbPTR1 (PDB-ID 5jdc) or a