Enzymology And Medicinal Chemistry Of N5-Carboxyaminoimidazole Ribonucleotide Synthetase : A Novel Antibacterial Target

ENZYMOLOGY AND MEDICINAL CHEMISTRY OF N-CARBOXYAMINOIMIDAZOLE RIBONUCLEOTIDE SYNTHETASE:A NOVEL ANTIBACTERIAL TARGETbyHANUMANTHARAO PARITALAAUGUST 2010Advisor: Dr. Steven M. FirestineMajor: Pharmaceutical SciencesDegree: Doctor of PhilosophyN-Carboxyaminoimidazole ribonucleotide synthetase (N-CAIRsynthetase), a key enzyme in microbial de novo purine biosynthesis, catalyzes theconversion of aminoimidazole ribonucleotide (AIR) to N-CAIR. To date, thisenzyme has been observed only in microorganisms, and thus, it represents anideal target for antimicrobial drug development. Here, we report structural andfunctional studies on the Aspergillus clavatus N-CAIR synthetase and identification of inhibitors for the enzyme. In collaboration with Dr. Hazel Holden ofthe University of Wisconsin, the three-dimensional structure of Aspergillus clavatusN-CAIR synthetase was solved in the presence of either Mg2ATP or MgADP andAIR. These structures, determined to 2.1 and 2.0 Å resolution, respectively,revealed that AIR binds in a pocket analogous to that observed for other ATP-grasp enzymes involved in purine metabolism. On the basis of these models, asite-directed mutagenesis study was subsequently conducted that focused on five