Orotidine 5'-monophosphate decarboxylase (ODCase) is a key enzyme in the de novo pyrimidinebiosynthetic pathway. This pathway is essential for the biosynthesis of building blocks for both DNA andRNA, and thus inhibitors of ODCase could have significant therapeutic value. Despite recent significantadvances, it is not understood what factors are important in binding to and catalysis by ODCase. Thelack of such knowledge is a critical defecit because understanding these factors is essential to thedesign of potent inhibitors for this enzyme. Our long-range goal is to understand the catalyticmechanism of ODCase and to design potent inhibitors of ODCase based on the mechanism. Theobjective of this application, which is a step in pursuit of that goal, is the identification of structuralcomponents of the substrate and its analogs that are important for binding and catalysis. The centralhypothesis of the application is that the zwitterionic content (determined by proton affinity) is the mostimportant factor in determining the rate of decarboxylation in model and enzyme-catalyzed reactions aswell as the tightness of binding and that binding energy from remote binding sites is utilized by ODCaseto catalyze the reaction. The hypothesis will be tested by pursuing the following two specific aims: 1)Identify the role played by the zwitterionic intermediate in the model and enzymatic decarboxylation ofsubstrate analogs and identify the structural components on the pyrimidine ring of the substrate andanalogs that are important for binding and catalysis; and 2) Determine the role of remote binding sites(the hydroxy groups on the ribose moiety) toward binding and catalysis. The proposed research isinnovative because it combines model and enzymatic studies to identify the role of zwitterioic structuresin the reaction mechanism and to determine the factors important for binding and catalysis. Thiscontribution is significant, therefore, because it will provide an understanding of how enzymes utilizeremote binding energy in catalysis in general, and the mechanism as well as the design of potent andselective inhibitors of ODCase, in particular.Relevance to Public Health: It is of great interest to develop potent inhibitors of ODCase because it ispart of the nucleic acid biosynthesis machinery. Inhibition of the biosynthesis of these building blockshas been exploited in cancer chemotherapy. Many other pyrimidine antagonists have been shown to beuseful in antitumor and antiviral chemotherapy
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