Discovery of Staphylococcus aureus bacteria cell division FtsZ protein inhibitors via STD NMR

Publication Type:
Thesis
Issue Date:
2014
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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- The increase of antibiotic resistance among an array of bacteria has engendered a search for antibiotics with novel modes of action. Pathogens such as Methicillin-resistant Staphylococcus aureus (MRSA) have shown resistance towards every class of antibiotics available and are of growing concern in both hospital and community settings. Hence, targeting bacterial cell division proteins is a new approach in developing new antibiotics. One such emerging target is FtsZ, a cell division protein that is highly conserved among bacteria and found to be an essential protein in 1990. Although berberine has been shown to inhibit FtsZ in Escherichia coli, optimization of this drug was necessary. Thus, this thesis further investigates the potential of using natural products to inhibit bacterial cell division such as berberine, eugenol, cinnamaldehyde, and synthesised berberine-like molecules by targeting S. aureus FtsZ (SaFtsZ). Berberine-like molecules, 4 and 4a were successfully synthesised and their inhibitory activity analysed via Saturation Transfer Difference Nuclear Magnetic Resonance (STD NMR) and minimum inhibitory concentrations (MIC). STD NMR standard operation procedures were first developed and optimised for implementation on an Agilent 500 MHz NMR by way of a model study using human serum albumin and tryptophan as the protein and ligand, respectively. SaFtsZ was overexpressed and purified for STD NMR studies and the procedures were successfully applied in the investigation of SaFtsZ-ligand interactions. Following comparative analysis with molecular modelling, compounds with benzene conjugated systems and nitro substituted benzene rings were found to improve SaFtsZ binding affinity. Biological assays of the five compounds were utilised to assess the potency of each compound. This was accomplished via MIC assays to determine the lowest concentration required to inhibit the growth of S. aureus ATCC25923, and berberine was found to have MIC value of 128 μg/mL, two serial dilutions less than MIC values of eugenol, cinnamaldehyde, 4 and 4a.
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