Role of peptidoglycan-active enzymes in the assembly of bacterial motility, secretion and efflux systems

点击翻译按钮获取中文摘要

Peptidoglycan (PG) is a major structural component of bacterial cell walls but is absent in higher organisms. It is a strong, chain link fence-like material with a pore size of ~100 kDa. It completely surrounds bacteria, providing protection against high internal pressures and contributing to the formation of distinct bacterial cell shapes. Although PG is essential for bacterial viability and was identified decades ago as the target of the earliest antibiotics, the molecular details of its synthesis are only partly understood. In part, this lack of understanding has arisen because most bacteria have multiple, non-essential PG active enzymes with seemingly redundant activities, making it challenging to assign specific functions to individual proteins. Drugs such as penicillin that inhibit PG synthesis often target multiple enzymes simultaneously, making it hard to determine if loss of one or more proteins is responsible for the observed killing effects. On the physical side, PG is a single, gigantic covalently linked polymer that has been difficult to characterize at the level of resolution needed to understand the contribution of individual proteins. Among the things we need to know are what individual proteins do, when and where they do it, and how their activities affect the assembly of large protein complexes that pass through the PG layer to the outside of the cell. Such complexes include those involved in the key processes of motility, protein secretion and efflux of toxic compounds. Using bacteria lacking single PG-active enzymes, we have undertaken a long term research program to understand how the control of PG metabolism and structure intersects with assembly of cell-wall-spanning protein complexes. Through phenotypic screens, we have identified an amidase and a PBP that are required for normal assembly of motility and secretion systems; and a different PBP and a lytic transglycosylase that act as sentinels of cell wall damage as well as having roles in the assembly of drug efflux pumps, both processes that lead to antibiotic resistance. Our research will lead to new strategies to overcome antibiotic resistance, an increasingly serious problem threatening the health of Canadians, as strains resistant to all known antibiotics are already here.