Prof Colin Kleanthous

Protein-protein interactions in the Gram-negative bacterial cell envelope

Bacteria envelope themselves in robust layers of membrane and cell wall that are vital to their survival. Using a variety of biochemical, structural, biophysical and cell-based approaches, we investigate interactions between proteins that build and maintain the cell envelope in Gram-negative bacteria and how bacteriocins exploit protein-protein interactions to navigate through these layers in order to kill bacteria.

Protein bacteriocins – We study how these 30-80 kDa toxins assemble translocon complexes at the cell surface and how these trigger import across one or both membranes. Our principal target organisms are also major pathogens that have seen dramatic rises in antibiotic resistance, including Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. In collaboration with colleagues in Scotland, we have shown that bacteriocins can be used to treat multidrug resistant bacterial infections. These developments are the basis for Glox Therapeutics, a new protein antibiotics spin out supported by seed investment from Boehringer Ingelheim Venture Fund and Scottish Enterprise.
Outer membrane organisation – Our recent work challenges accepted dogma that the Gram-negative outer membrane is an asymmetric lipid bilayer. We have shown that the E. coli outer membrane is more akin to an asymmetric proteolipid membrane where β-barrel outer membrane proteins are interlinked by shared lipopolysaccharides forming an expansive network that covers the cell. Insertion of outer membrane proteins into this rigid environment by the BAM complex is cell cycle dependent even though BAM is found throughout the membrane. In collaboration with colleagues in Australia, we demonstrated that this spatiotemporal regulation is the result of the peptidoglycan layer controlling BAM activity, enabling bacteria to synchronise growth of these two layers of the cell envelope.
Energy transduction to the outer membrane – The outer membrane is not energised but many processes require energy to proceed. Gram-negative bacteria solve this problem using assemblies that span the cell envelope and convert the electrochemical potential of the proton motive force into mechanical work at the outer membrane. We investigate how these energy transduction systems work, focusing on Ton and Tol-Pal that import nutrients and stabilise the outer membrane, respectively. We recently discovered how the level of force delivered by these systems, and hence the physiological outcome, can be manipulated.

For further information, see: https://kleanthouslab.web.ox.ac.uk