LipidII‐DegradingM‐Class Bacteriocins

Abstract

Lipid II ‐degrading M‐class bacteriocins are protein antibiotics that kill a narrow spectrum of bacterial strains through cleavage of lipid II , thereby leading to an arrest of cell wall synthesis and cell lysis. A number of M‐class bacteriocins have been structurally and functionally characterized, which include colicin M from Escherichia coli , syringacin M from Pseudomonas syringae , and pyocin M (PaeM) from P. aeruginosa . In each case, these bacteriocins have been shown to kill bacteria closely related to the producing strain, with selectivity mediated through the presence of a specific outer membrane receptor. Cell killing requires uptake of the bacteriocin into the periplasm where it is able to cleave lipid II in a metal‐dependent manner. Calcium and magnesium have been shown to support enzymatic activity, and X‐ray crystal structures of syringacin M and PaeM, respectively, show these ions bound at the putative active site. Extensive structural and mutagenesis studies have enabled delineation of the functional domains of the M‐class bacteriocins that mediate receptor binding, translocation across the outer membrane, and cytotoxic activity.