Structural and biophysical characterization of proteins involved in cell wall and capsule synthesis in the pathogen Mycobacterium tuberculosis

Our group applies X-ray crystallography, and a range of other biophysical techniques to investigate the molecular basis of cell wall and capsule synthesis in Mycobacterium tuberculosis, the organism responsible for tuberculosis. Despite dedicated containment efforts by the World Health Organisation, tuberculosis remains a health problem of global proportion, compounded by the rise of multi-drug and extensive drug-resistant forms of the tubercle bacillus. In this context, biosynthesis of the mycobacterial cell wall and capsule is of great interest: one, its unique structure and architecture involves a great deal of novel biochemistry; two, enzymes and proteins involved in cell wall biosynthesis may be exploited as potential targets for urgently needed new chemotherapeutics that can ease the threat posed by drug-resistant bacilli.

In collaboration with Prof. Besra’s laboratory (U. Birmingham), our work focusses on two distinct pathways, arabinan and glucan capsule synthesis. Cell wall arabinan, a polymer of arabinofuranose saccharides, is an essential component of characteristic cell wall core, but also occurs as a part of the membrane-anchored glycolipid lipoarabinomannan. The latter is an important modulator of the host immune system. We have recently solved the crystal structure of the flavoenzyme DprE1. This enzyme helps synthesise a key precursor of cell wall arabinan, and is a highly attractive potential drug target. We seek to characterize complex structures of DprE1 bound to new anti-tubercular inhibitors, while at the same time seeking to understand its catalytic mechanism and interaction with DprE2, the enzyme acting in concert with DprE1.

A second line of investigation is devoted to the pathway of glucan capsule synthesis in M. tuberculosis. This outermost layer of mycobacteria is not essential in culture, but plays a key role in persistence in the host. A sequence of four enzyme-catalysed reactions leads from the relatively abundant disaccharide trehalose to a structure of branched glucose polymer, that is synthesized in the cytoplasm before export to the extracellular surface. We have found biophysical evidence for complex formation between enzymes involved in this pathway, which includes two genetically verified drug targets, and obtained a structure of one of the key players.

The training involved in these projects will include molecular biology, protein expression and purification, X-ray crystallographic analysis and various spectroscopic techniques. Participation in experiments at synchrotron beamlines is typically involved as well.
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Please find additional funding text below. For further funding details, please see the ‘Funding’ section.
The School of Biosciences offers a number of UK Research Council (e.g. BBSRC, NERC) PhD studentships each year. Fully funded research council studentships are normally only available to UK nationals (or EU nationals resident in the UK) but part-funded studentships may be available to EU applicants resident outside of the UK. The deadline for applications for research council studentships is 31 January each year.

Each year we also have a number of fully funded Darwin Trust Scholarships. These are provided by the Darwin Trust of Edinburgh and are for non-UK students wishing to undertake a PhD in the general area of Molecular Microbiology. The deadline for this scheme is also 31 January each year.