Bacterial cell division ; a novel target for new antibacterials
- Publication Type:
- Thesis
- Issue Date:
- 2019
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The problem of antibiotic resistance is a complex issue and one that urgently needs addressing from multiple sectors, including agriculture, medicine, science/research, government, social science, businesses and the community. Although many strategies are being implemented around the world to address these different aspects that contribute to the rise and spread of antibiotic resistance, one further possibility to help alleviate this problem is through the design of novel antibiotics. The essential process of bacterial cell division, is yet to be targeted by any of the FDA-approved antibiotics and represents an untapped area of potential drug targets. In this thesis, the overall strategy of inhibiting the bacterial cell division process is to target the essential and conserved protein FtsZ in two ways: Firstly, to understand the essential interaction of FtsZ with another division protein, FtsA as a starting point to design inhibitors of division complex formation and, secondly, to develop compounds that inhibit FtsZ function.
Characterizing the protein-protein interaction of FtsZ and its partner FtsA used the proteins from the organism Acinetobacter spp.. This is because A. baumannii is now classified by the World Health Organization as a priority 1 pathogen that urgently needs an antibiotic against due to its high multidrug resistance profile, as well as causing high mortality rates. Two of the most highly conserved bacterial cell division proteins, FtsZ and FtsA, have been recognised as promising drug targets in Acinetobacter spp. and other bacteria. The interaction of these two proteins has been known for over a decade with mutational studies indicating that the conserved aspartate and proline at the extreme C-terminal peptide of FtsZ being the important amino acid residues for the interaction of FtsZ and FtsA in Escherichia coli and other bacterial species. Co-crystallography of Thermotoga maritima FtsZ C-terminal peptide and FtsA identified an additional amino acid; arginine, to be important in the interaction of FtsZ and FtsA. In the Acinetobacter spp. the aspartate, proline and arginine have been changed to a serine, glutamine and lysine, respectively. Understanding this could potentially be used to develop new narrow-spectrum antimicrobials to specifically treat Acinetobacter infections. The work in this thesis attempted to understand the implication of these amino acid differences by initially conducting an in silico study. The data obtained suggests that the serine, glutamine and lysine are important for the FtsZ/FtsA interaction of Acinetobacter spp. Further follow up co-crystallographic studies were planned using full-length Acinetobacter FtsZ and FtsA. Both of these full-length Acinetobacter proteins were successfully purified in this study but, the purified FtsZ protein was unable to form crystals of acceptable size for structure determination, while the purified FtsA were found to be aggregated. Therefore, in the interest of time and for gaining positive results, the focus of the project was shifted towards solely understanding and targeting FtsZ.
Thus far, many published FtsZ inhibitors have been shown to target FtsZ in one of the three druggable regions on the protein: nucleotide-binding domain, interdomain cleft and T7-loop. A missing piece of information is an in-depth understanding of FtsZ structure at the molecular level across diverse bacterial species to ensure inhibitors have high affinity for the FtsZ target in a variety of clinically relevant pathogens. To address this, an in silico investigation was conducted by analysing multiple FtsZ structures, which revealed that FtsZ groups into two distinct classes based on structural differences. The outcome of this analysis lead to the suggestion of several binding pockets on FtsZ which can potentially be used as a broad- and narrow-spectrum target. The use of fragment-based drug discovery approach, allowed the confirmation of one of the suggested pockets, which is located towards the front of the nucleotide-binding domain. This pocket is yet to be reported in the literature, therefore, allowing the possibility of novel drug design to contribute in tackling the global issue of antimicrobial resistance.
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