Cloning, characterization and validation of inosine 5'-monophosphate dehydrogenase of Babesia gibsoni as molecular drug target

The inosine monophosphate dehydrogenase (IMPDH) enzyme has been characterized and validated as a molecular drug target in other apicomplexans but not in the genus Babesia. Subsequently, we cloned and expressed a Babesia gibsoni IMPDH (BgIMPDH) cDNA in Escherichia coli. We also determined the inhibitory effect of mycophenolic acid (MPA) on recombinant BgIMPDH (rBgIMPDH) activity and the Babesia-growths in vitro. The translated BgIMPDH peptide contained thirteen amino acid residues responsible for substrate and cofactor binding in its catalytic domain with Gly374 in BgIMPDH being replaced by Ser388 in mammalian IMPDH. The native BgIMPDH enzyme in the parasite was approximately 54-kDa a mass similar to His-tag rBgIMPDH protein. The K_m values of the rBgIMPDH were 8.18±0.878 (mean±standard error of the mean) μM and 360.80±43.41μM for IMP and NAD⁺, respectively. MPA inhibited the rBgIMPDH activity yielding a K_i value of 20.93±1.83μM with respect to NAD⁺. For Babesia growths, the IC₅₀s were 0.95±0.21 and 2.88±0.49μM for B. gibsoni and B. bovis, respectively. Therefore, our results suggest that MPA may inhibit the replication of Babesia parasites by targeting IMPDH enzyme of the purine pathway.