Elucidating the mechanisms of outer membrane biogenesis

This project focuses on characterising the fundamental process of inter membrane phospholipid transport in Gram-negative bacteria, a largely unknown process which is only now being revealed.

The emergence of bacteria that are resistant to available antibiotics represents an enormous and growing global threat requiring new targets and strategies to combat infection. Multidrug resistance is most serious for Gram-negative bacteria, with essentially few antibiotics under development or likely to be available for clinical use in the near future.

The bacterial cell envelope has been and still remains one of the best targets for antimicrobials development. For a successful antibacterial drug development programme a detailed understanding of envelope structure and biogenesis is required. In Gram-negative bacteria the envelope is a complex, essential tripartite structure formed by two membranes sandwiching a peptidoglycan layer that together maintain the integrity and the shape of the cell. While the structure and composition of the bacterial cell envelope has been known for a number of years, details on its biogenesis have only recently emerged. These processes can be exploited for antimicrobial discovery as they are not present in humans. In particular, the outer membrane has been focused on as it makes direct contact with the host. Furthermore, the lipid components of this membrane, lipopolysaccharides in the outer leaflet, and phospholipids in the inner leaflet, are essential for Gram-negative survival and produce a membrane that is very resistant to antibiotics, detergents and other toxic chemicals. It is built by sophisticated and complex multi-protein machineries: proteins via the Bam machinery, lipoproteins via the Lol pathway and lipopolysaccharides via the Lpt pathway. Phospholipid transport however has remained elusive until now.

Recently three protein pathways, the Mla, PqiABC and YebST pathways, have been identified that have components in the inner membrane, periplasm and outer membrane and all bind phospholipid suggesting they may be involved in phospholipid transport. Indeed our recent research in to the Mla pathway (Nature Microbiology) has shown that this pathway can function to transport phospholipids towards the outer membrane and is the first evidence of a phospholipid transport pathway to the outer membrane in Gram-negative bacteria. How these pathways transport phospholipid and the molecular mechanisms involved in transport still remain to be elucidated however. By using a multidisciplinary approach, working in the fields of both biophysics and molecular biology, this project will provide valuable insight in to the fundamental process of phospholipid transport and potentially identify druggable pockets and novel compounds that will not only abolish virulence but also impede restoration of a damaged OM and therefore potentially lead to the development of new classes of antimicrobials.