Unifying regulatory mechanism of bacterial cell wall synthesis

Abstract

Bacteria are surrounded by a peptidoglycan (PG) cell wall that serves as a protective layer against environmental insults and guides the processes of cell division and morphogenesis. Peptidoglycan is produced from the lipid II precursor in two enzymatic steps: glycosyltransferase (GT) enzymes polymerize lipid II into glycan strands, which are then crosslinked by transpeptidases (TP) to expand the meshwork. Bacteria rely on two families of essential and ubiquitous PG synthases to accomplish PG synthesis. Class A penicillin-binding proteins (aPBPs) are bifunctional PG synthases, whereas class B PBPs are monofunctional transpeptidases that function in tandem with glycosyltransferases from the SEDS family. While SEDS-bPBPs and aPBPs are enzymatically equivalent, they share little structural homology and participate in distinct physiological processes in cells – bacterial elongation, division and peptidoglycan fortification and repair. Genetic studies implicate cellular accessory factors in the spatiotemporal control of their cognate PG synthases and show that loss of enzymatic coordination underlies the lethal action of penicillin-type antibiotics. Despite the profound importance of proper PG biogenesis for bacterial physiology, the molecular details and functional consequences of these regulatory pathways have remained unclear. Here, we investigate the molecular mechanisms that control cellular activation and dynamics of two prototypical E. coli SEDS-bPBP and aPBP synthases. Our work shows that these structurally and functionally divergent families rely on the same global molecular logic of PG synthesis regulation, whereby accessory factor binding triggers enzymatic activation through structural rearrangements at the interface between the GT and TP enzymatic domains. The conformational switches that we uncovered provide promising new avenues for future antibiotic development.