HYPOXANTHINE PHOSPHORIBOSYLTRANSFERASE FROM TRYPANOSOMA-CRUZI AS A TARGET FOR STRUCTURE-BASED INHIBITOR DESIGN - CRYSTALLIZATION AND INHIBITION STUDIES WITH PURINE ANALOGS

The hypoxanthine phosphoribosyltransferase (HPRT) from Trypanosoma cru zi is a potential target for enzyme structure-based inhibitor design, based on previous studies which indicate that these parasites lack the metabolic enzymes required for de novo synthesis of purine nucleotide s. By using a bacterial complement selection system, 59 purine analogs were assayed for their interaction with the HPRTs from T. cruzi and H omo sapiens. Eight compounds were identified from the bacterial assay to have an affinity for the trypanosomal enzyme, Inhibition constants for four of these compounds against purified recombinant trypanosomal and human HPRTs were determined and compared. The results confirm that the recombinant system can be used to identify compounds which have a ffinity for the trypanosomal HPRT. Furthermore, the results provide ev idence for the importance of chemical modifications at positions 6 and 8 of the purine ring in the binding of these compounds to the HPRTs, An accurate three-dimensional structure of the trypanosomal enzyme wil l greatly enhance our understanding of the interactions between HPRTs and these compounds, Toward this end, crystallization conditions for t he trypanosomal HPRT and preliminary analysis of X-ray diffraction dat a to a resolution of 2 Angstrom is reported, These results represent s ignificant progress toward a structure-based approach to the design of inhibitors of the HPRT of trypanosomes with the long-range goal of de veloping new drugs for the treatment of Chagas' disease.