Drug targets in Mycobacterium tuberculosis α-glucan synthesis

Batey, Sibyl (2017) Drug targets in Mycobacterium tuberculosis α-glucan synthesis. Doctoral thesis, University of East Anglia.

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Abstract

α-Glucans are important energy storage polysaccharides in bacteria, plants and animals. In Mycobacterium tuberculosis, α-glucan also functions as a virulence factor that is exported to the mycobacterial capsule and interacts with human immune receptors. In M. tuberculosis and other actinomycetes, α-glucan is synthesised from maltose-1-phosphate by the maltosyl transferase GlgE and the α-1,6-branching enzyme GlgB. These enzymes have been genetically validated as tuberculosis drug targets. The loss of the α-glucan virulence factor is exacerbated by the toxic accumulation of maltose-1-phosphate, which results in a pleiotropic stress response and cell death.

α-Glucan produced by this pathway has shorter branches than classical bacterial α-glucan, but the mechanistic basis of this was not fully understood. To address this, I produced α-glucan in vitro, demonstrating GlgE and GlgB alone were sufficient to generate the distinct architecture. To investigate the determinants of α-glucan branch lengths, I solved high resolution crystal structures of Mycobacterium smegmatis GlgB bound to different oligosaccharides. These enabled the identification of several substrate binding sites, including the donor and acceptor sites of a newly forming branchpoint, giving novel insights into the action of glucan branching enzymes.

To address M. tuberculosis GlgB as a drug target, I developed a high-throughput screening assay and used this to identify a potent, small-molecule inhibitor. I synthesised a selection of analogues to investigate structure-activity relationships. I also assessed the action of the compounds in vivo, demonstrating growth inhibition at high concentrations, but not via the GlgB target. Finally, I explored trehalose analogues as potential precursors for GlgE inhibitors, focussing on the synthesis, uptake and processing of 4-deoxy trehalose analogues.

This multidisciplinary work gives a deeper understanding of mycobacterial α-glucan synthesis and how this can be targeted to develop new tuberculosis therapeutics.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Bruce Beckett
Date Deposited: 24 Jul 2018 10:19
Last Modified: 06 Dec 2019 01:38
URI: https://ueaeprints.uea.ac.uk/id/eprint/67832
DOI:

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