STRUCTURE BASED DRUG DISCOVERY AND MECHANISTIC STUDIES OF PHOSPHORIBOSYLTRANSFER

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many parasites lack de novo pathways for purine nucleotide biosynthesis and rely on salvage enzymes, such as the phosphoribosyltransferases, to acquire those needed for cellular metabolism, thus, the salvage pathways provide targets for anti-proliferative drug discovery. In addition, we are interested in studying the mechanism of hypoxanthine/guanine phosphoribosyltransferases, which catalyze a reversible, ordered, sequential, nucleophilic displacement reaction utilizing two divalent metal ions, which straddle the pyrophosphate leaving group, position the two substrates, and interact with an invariant aspartic acid residue. Closed active site forms of ternary complexes of the Trypanosomza cruzi and human enzymes are available that allow us to analyze structures captured right before the transition states of both the forward and reverse reactions, using a combination of natural substrates or products, and analogs. The closed active site ternary substrates complex of the HPRT from T. cruzi was targeted with DOCK, and several low micromolar inhibitors were further identified that were obtained directly from computational analyses. Many more compounds await characterization. Structures of complexes of the target with inhibitors will allow comparison of predicted to actual binding modes, and comparisons of parasite and human enzymes in complex with inhibitors might lend insight toward improving selectivity for the parasite enzymes.