Expression, purification, crystallization and preliminary X‐ray analysis of a nucleoside kinase from the hyperthermophile Methanocaldococcus jannaschii

Methanocaldococcus jannaschii nucleoside kinase ( Mj NK) is an ATP‐dependent non‐allosteric phosphotransferase that shows high catalytic activity for guanosine, inosine and cytidine. Mj NK is a member of the phosphofructokinase B family, but participates in the biosynthesis of nucleoside monophosphates rather than in glycolysis. Mj NK was crystallized as the apoenzyme as well as in complex with an ATP analogue and Mg 2+ . The latter crystal form was also soaked with fructose‐6‐phosphate. Synchrotron‐radiation data were collected to 1.70 Å for the apoenzyme crystals and 1.93 Å for the complex crystals. All crystals exhibit orthorhombic symmetry; however, the apoenzyme crystals contain one monomer per asymmetric unit whereas the complex crystals contain a dimer.