Doctor of Philosophy (PhD)
An urgent demand for the development of new antibiotics has been created by the increase in clinical cases involving drug-resistant pathogenic bacteria. A novel target for antibacterial development is acetyl-CoA carboxylase, a multifunctional enzyme that catalyzes the first committed step in fatty acid synthesis. The bacterial form of the enzyme consists of three proteins: biotin carboxylase, biotin carboxyl carrier protein, and carboxyltransferase. The research presented in this dissertation describes dual-ligand inhibitors incorporating selective inhibitors against biotin carboxylase and carboxyltransferase that were synthesized by covalently attaching them with saturated hydrocarbon linkers containing 7 and 15 carbon atoms. The ability to inhibit two different enzymes with the same compound expounds on the theory of increasing overall potency and impeding the ability for the development of resistance. Kinetic results revealed both dual-ligands displayed inhibition constants in the nanomolar range. However, microbiology assays showed the dual-ligand with the longer linker did not exhibit antibacterial activity. The dual-ligand with the shorter linker showed antibacterial activity against both Gram-positive and Gram-negative organisms as well as decreased susceptibility to the development of bacterial resistance. These results suggest that the length and chemical properties of the covalent linker is critically important for maintaining the antibacterial activities of the two incorporated pharmacophores. Based on biochemical activities, likely reflects alteration in cell permeability or avoidance of intrinsic efflux of the tested dual-ligand molecules. The natural product moiramide B is a broad spectrum antibiotic that inhibits the carboxyltransferase component of acetyl-CoA carboxylase. A crystal structure of moiramide B was solved in complex with carboxyltransferase. The structure shows that only the (S)-methyl pyrrolidinedione head group of moiramide B is used to inhibit the enzyme by taking advantage of the two oxyanion holes that the enzyme normally uses to stabilize enolate anions that form in the substrates during catalysis. The fatty acid tail of moiramide B appears to be only needed for entry into the bacterial cell. Structure-activity relationship studies validated the necessary structural features that contribute to the inhibitory and antibacterial properties of moiramide B. These findings can lead to further design and development of a potent carboxyltransferase antibacterial agent.
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Silvers, Molly Anne, "Design, Synthesis, and Antibacterial Properties of Dual-Ligand Inhibitors of Acetyl-CoA Carboxylase and Mechanism of Action for the Antibacterial Agent Moiramide B" (2014). LSU Doctoral Dissertations. 820.