The role of species-specific modifications in peptidoglycan biosynthesis
Peptidoglycan is an essential structural component of most bacteria which forms the cell wall; a mesh like structure that surrounds the cell and is essential for cell survival. It is composed of glycan chains of alternating N- acetylglucosamine and N-acetylmuramic acid linked by short crosslinking polypeptides. Crucially for the cell, it withstands cellular turgor pressure as well as serving as an anchor for additional components of the cell envelope.
Penicillin binding proteins (PBPs) are responsible for the polymerisation of the glycan chains which make up peptidoglycan (transglycosylation) as well as glycan-chain crosslinking (transpeptidation). The PBPs are excellent targets for antimicrobial drugs as they are essential (in most cases) for the cell to survive and the same enzymes are not found in humans. However, high levels of resistance have developed to these drugs through numerous well-defined mechanisms.
Characterisation of the essential Class A PBPs from Gram-positive bacteria (Streptococcus pneumoniae specifically) and their interactions is essential in both understanding the mechanisms of peptidoglycan biosynthesis and enabling the development of new classes of antibiotics. We are using new and established assays of transglycosylase activity to study the activity of class A PBPs with lipid II substrate variants and enzyme mutants. Coordinated activities of combinations of enzymes can also be studied with complementary techniques to look at protein-protein interactions supporting it.