Title: Characterising a new family of glycoside hydrolases that target mycobacterial cell wall glycans
Funder: The Academy of Medical Sciences

Abstract: The cell walls of pathogenic mycobacteria including the causative agent of Tuberculosis, M. tuberculosis, contribute to their pathogenicity and resistance to many common antibiotics. We have discovered a novel family of enzymes expressed by glycan degrading bacteria from the human gut that are able to break down one of the most unusual components of the mycobacterial cell wall, 🇩-arabinan. 🇩-arabinan is a critical part of two different polymers of the mycobacteria cell wall, the structural glycan arabinogalactan, and the important immunomodulatory glycolipid lipoarabinomannan. Excitingly, this new family of enzymes (AraH) has conserved homologues throughout mycobacteria, some of which have been previously identified in genetic screens to have a role in mycobacterial control of the phagosome. We hypothesise that mycobacteria use these enzymes to release the immunogenic lipoarabinomannan during infection. This proposal aims to biochemically and structurally characterise members of the AraH family from pathogenic mycobacteria, including M. tuberculosis, M. abscessus, M. avium and M. leprae, with the ultimate aim of understanding their role in mycobacterial cell biology and infection. We will express, purify and undertake detailed enzymatic analyses of these proteins, to characterise their activity towards arabinogalactan and lipoarabinomannan, and aim to obtain crystal structures to enable design of inhibitors. These data will form the framework for future investigations into both the biological role of AraH in mycobacteria, and the potential of these enzymes as lytic tools for mycobacterial diagnostics.

Lay abstract: Infectious bacteria such as Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis (TB), and its relatives have a tough cell wall made primarily of complex sugar polymers (called glycans) and lipids. This wall ensures the bacterium’s structural integrity. The chemical structure of the Mtb cell wall is complex and unusual, and is one of the reasons why TB is so difficult to treat with antibiotics. New strategies to diagnose and combat TB are urgently needed, as it is currently responsible for 1.5 million deaths per year. Additionally, each year there are more infections from strains of Mtb that are resistant to the antibiotics currently used to treat TB, so new approaches are essential. We have discovered a new family of enzymes able to break down the cell wall glycans of Mtb and other infectious mycobacteria. Excitingly, we have found copies of these enzymes in Mtb itself. Prior studies have pointed to an important role for these Mtb enzymes during infection, suggesting they could be targets for future drug development for control of TB. In this proposal we will test the activity of the enzymes from Mtb and others to determine how they function and which precise sugar structures they target. We will determine the molecular structures of these enzymes to guide the design of inhibitors, which could be used as drug treatments in the future. We will also use the enzymes to help develop better tests for rapidly diagnosing Mtb infections.

Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS;2.2 FACTORS RELATING TO PHYSICAL ENVIRONMENT
Health categories: INFECTION