Molecular and biochemical studies on the hypoxanthine-guanine phosphoribosyltransferases of the pathogenic haemoflagellates

All genera of protozoan parasites are auxotrophic for purines, and thus, purine acquisition from the host is a nutritional necessity for the survival and growth of these pathogens. Many of these parasites, including Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp., access host purines by phosphoribosylating purine bases via purine phosphoribosyltransferase (PRT) enzymes. The trypanosomatid hypoxanthine-guanine phosphoribosyltransferase (HGPRT) enzyme has been implicated as a critical enzyme of purine salvage in members of the Trypanosomatidae family. Moreover, the HGPRT enzymes of Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. can also initiate the metabolism of certain cytotoxic purine base analogs that have little effect on the mammalian host. This implies that either inhibitors or substrates of HGPRT might serve as efficacious and selective agents for the treatment of diseases for which trypanosomatids are the etiologic agent. The hgprt genes from Trypanosoma brucei, Trypanosoma cruzi and Leishmania donovani have all been cloned, sequenced and overexpressed in E. coli, and the recombinant proteins have all been purified to homogeneity and characterized with respect to kinetic parameters and physicochemical properties. This paper presents an overview of recent molecular and biochemical studies on trypanosomatid HGPRT proteins and future efforts to validate HGPRT as a rational target for the chemotherapeutic manipulation of African sleeping sickness, Chagas disease and leishmaniasis.