Use of a repetitive seeding protocol to obtain diffraction‐quality crystals of a putative human
In mammals, the enzyme d‐xylulokinase (XK; EC 188.8.131.52) catalyses the last step of the glucuronate–xylulose pathway, in which the ketopentose sugar d‐xylulose is phosphorylated to yield d‐xylulose
5‐phosphate (Xu5P). Xu5P is also a metabolite of the pentose phosphate pathway and acts as a signalling molecule that regulates lipogenesis and glycolysis in the liver. To date, no eukaryotic XK has been structurally characterized. A putative human XK was expressed in Escherichia
coli aided by molecular chaperones, purified and crystallized. A seeding procedure involving repeated rounds of seeding was developed and proved to be essential for obtaining diffraction‐quality crystals. Preliminary X‐ray diffraction analysis was performed using synchrotron
radiation. This resulted in the collection of a complete diffraction data set to 2.7 Å resolution from a crystal belonging to the trigonal space group P31 or P32 with unit‐cell parameters a = b = 101.87, c = 158.85 Å.