Protein complexes required for bacterial cell wall biosynthesis and division

Antimicrobial Resistance (AMR) is now widely understood to be a global healthcare emergency, exacerbated by many socio-economic factors. This includes the decline in new drug development due to disengagement from the sector by the major pharmaceutical companies resulting in a renewed emphasis on academic engagement in discovery and understanding of how resistance develops. Of all the targets for antibiotics and resistance development, the biosynthesis of the bacterial cell wall and its linkage to cell division is of particular significance it is the entry point for all antibiotics into bacteria as well as the target for the mainstay of antimicrobial chemotherapy: the b-lactams.

Outside the cytoplasmic membrane of all bacteria, there is a sugar-based polymer called peptidoglycan (PG) crosslinked by peptide bridges, which gives the cell wall strength, rigidity, cell shape characteristics and is a scaffold for a multitude of other molecular structures. Disruptions of the PG structure itself or its biosynthetic precursors by antibiotics, can result in cell lysis (bacteriolytic effect) or cessation of bacterial cell growth (bacteriostatic effect). Recently there has been a renascence in our understanding of the biosynthesis of the cell wall and how this is intimately linked to cell division1. Whilst we have recognised this process for decades2, the molecular interactions that are vital and underpin the biology of this process, are only just starting to be properly addressed.

The biosynthesis of PG requires the polymerisation of its lipid linked disaccharide-pentatpeptide monomer unit: lipid II into a glycan polymer3 by the glycosyltransferase activity of either Class A penicillin binding proteins1 (PBPs e.g. PBP1a) of by Shape elongation and division proteins (SEDs: e.g. RodA)4. A cross linked PG layer is then produced by the formation of peptide bonds between the pentapeptides on adjacent glycan strands. This is catalysed by the transpeptidase activity of Class A alone or complexes of SEDs proteins with class B PBPs. This latter activity is inhibited directly by beta-lactams whilst the former offers exciting new opportunities for antibiotic drug discovery5.

In our laboratory we are focussed on two aspects of this process. How the cell wall PG is made by the SEDs-Class B PBP complexes and how the process of cell division is coordinated with PG biosynthesis in both Gram-positive and Gram-negative pathogens. As shown in the figure these proteins are intimately associated with the cell division (fts) proteins used in cell division and cell elongation and part of our research aims to understand these interactions. We use a variety of cutting-edge approaches to study this as well as collaboration with groups across the world in this research to allow a complete in-vivo to in-vitro approach. Importantly, our laboratory has two technological advantages over others including the ability to make the PG precursor lipid II allowing functional study of these proteins as enzymes and non-detergent methods to extract the membrane proteins involved in their native lipid environment6 allowing structural elucidation of their interactions at a molecular level.

The project will suit a student interested in microbiology, antibiotic resistance and biochemistry. Techniques used in this project can include basic microbiology, molecular biology including in-vivo mutant generation and phenotyping to protein chemistry and structural biology including X-ray crystallography, CryoEm microscope and mass spectrometry.

The ultimate PhD project will be developed with the student according to their interests and skill set with in a high collaborative research team environment. We urge students interested in the project to get in contact at earliest possible opportunity and engage in mini project opportunities.
Techniques that will be undertaken during the project:
- Basic microbiology and phenotyping of in-vivo mutants
- DNA cloning and site-directed mutagenesis.
- Protein expression and chemistry
- X-ray crystallography, CryoEM microscopy, Mass spectrometry