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 KM (434 ± 109 μM) and Vmax (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 Ki 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. [Display omitted] ► Obtained Leishmania donovani nucleoside hydrolase–maltose binding protein (LdNH–MBP). ► LdNH–MBP was showed to be a soluble, active and stable enzyme tested by NMR. ► Two quinolone nucleoside analogs were tested in vitro as inhibitors of LdNH–MBP. ► Compound 1 showed significant enzymatic activity decrease with Ki 1.6 ± 0.2 μM. ► These nucleosides analogs are new potential drugs for treatment of leishmaniasis.