Crystallization and preliminary X-ray structural analysis of nucleoside triphosphate hydrolases from Neospora caninum and Toxoplasma gondii

The nucleoside triphosphate hydrolases that are produced by Neospora caninum (NcNTPase) and Toxoplasma gondii (TgNTPase-I) have a different physio-logical function from the ubiquitous ecto-ATPases. The recombinant enzymes were crystallized at 293 K using polyethylene glycol 3350 as a precipitant and X - ray diffraction data sets were collected for NcNTPase (to 2.8 Å resolution) and TgNTPase-I (to 3.1 Å resolution) at 100 K using synchrotron radiation. The crystals of NcNTPase and TgNTPase-I belonged to the orthorhombic space group I222 (unit-cell parameters a = 93.6, b = 140.8, c = 301.1 Å) and the monoclinic space group P21 (unit-cell parameters a = 87.1, b = 123.5, c = 120.2 Å, β = 96.6°), respectively, with two NcNTPase (V M = 3.7 ų Da^-1) and four TgNTPase-I (V M = 2.7 ų Da^-1) molecules per asymmetric unit. SAD phasing trials using a data set (λ = 0.97904 Å) collected from a crystal of seleno-methionylated NcNTPase gave an initial electron-density map of sufficient quality to build a molecular model of NcNTPase.