Nucleoside triphosphate diphosphohydrolases (NTPDases) are secreted or membrane-bound ectonucleotidases that hydrolyze the anhydride bonds of nucleoside triphosphates and nucleoside diphosphates. Mammalian cell-surface NTPDase enzymes are inhibited by various polyoxometallates. Here, the structures of NTPDase1 from the bacterium Legionella pneumophila (LpNTPDase1) in complex with the dodecatungstate POM-1, decavanadate and octamolybdate/heptamolybdate are described. The metal clusters are bound at different sites but always in a highly ordered fashion via electrostatic interactions and hydrogen bonds. For octamolybdate, covalent interactions after oxygen ligand exchange by a serine and histidine side chain are also observed. The potential inhibitory mechanism and the use of the metal clusters as phasing tools for new NTPDase structures are discussed. The binding mode of a tartrate ion at the catalytic centre suggests novel strategies for the structure-based design of NTPDase inhibitors, and the observation of the enzyme in an intermediate open state contributes to our understanding of NTPDase enzyme dynamics.
Keywords: CD39; POM-1; apyrase; decavanadate; heptamolybdate; nucleotidase; octamolybdate.