Chagas disease, caused by the parasitic protozoan Trypanosoma cruzi, affects over 8 million people
worldwide. Current antiparasitic treatments for Chagas disease are
ineffective in treating advanced, chronic stages of the disease, and
are noted for their toxicity. Like most parasitic protozoa, T. cruzi is unable to synthesize purines de novo, and relies on the salvage of preformed purines
from the host. Hypoxanthine–guanine phosphoribosyltransferases
(HGPRTs) are enzymes that are critical for the salvage of preformed
purines, catalyzing the formation of inosine monophosphate (IMP) and
guanosine monophosphate (GMP) from the nucleobases hypoxanthine and
guanine, respectively. Due to the central role of HGPRTs in purine
salvage, these enzymes are promising targets for the development of
new treatment methods for Chagas disease. In this study, we characterized
two gene products in the T. cruzi CL
Brener strain that encodes enzymes with functionally identical HGPRT
activities in vitro: TcA (TcCLB.509693.70) and TcC
(TcCLB.506457.30). The TcC isozyme was kinetically characterized to
reveal mechanistic details on catalysis, including identification
of the rate-limiting step(s) of catalysis. Furthermore, we identified
and characterized inhibitors of T. cruzi HGPRTs originally developed as transition-state analogue inhibitors
(TSAIs) of Plasmodium falciparum hypoxanthine–guanine–xanthine
phosphoribosyltransferase (PfHGXPRT), where the most
potent compound bound to T. cruzi HGPRT
with low nanomolar affinity. Our results validated the repurposing
of TSAIs to serve as selective inhibitors for orthologous molecular
targets, where primary and secondary structures as well as putatively
common chemical mechanisms are conserved