Kinetics and docking studies of two potential new inhibitors of the nucleoside hydrolase from Leishmania donovani.

In this study the recombinant enzyme nucleoside hydrolase of Leishmania donovani (rLdNH) was expressed in Escherichia coli in connection with maltose binding protein (MBP). The rLdNH-MBP showed efficient a significant in vitro activity with inosine as substrate. From the coupled reaction with xanthine oxidase (XO) it was possible to determine the kinetic constants of rLdNH-MBP as K(M) (434 ± 109 μM) and V(max) (0.20 ± 0.02 μM). In addition, two nucleoside analogs (compounds 1 and 2) were tested as prototypes of rLdNH inhibitors. These compounds presented high affinity for the enzyme with K(i) values of 1.6 ± 0.2 and 17.0 ± 2.1 μM, respectively, as well as 271 and 26 folds higher than the affinity constant found for inosine. We also determined the type of enzyme inhibition, using double-reciprocal plot for these two compounds and the results confirmed a competitive inhibition. Additional docking studies showed the binding manner of compounds 1 and 2 inside the active site of LdNH revealing the essential residues for an effective inhibition. These results confirm that compounds 1 and 2 are strong rLdNH-MBP inhibitors.