Colicin M, a peptidoglycan lipid-II-degrading enzyme: potential use for antibacterial means?

Abstract

Colicins are proteins produced by some strains of Escherichia coli to kill competitors belonging to the same species. Among them, ColM (colicin M) is the only one that blocks the biosynthesis of peptidoglycan, a specific bacterial cell-wall polymer essential for cell integrity. ColM acts in the periplasm by hydrolysing the phosphoester bond of the peptidoglycan lipid intermediate (lipid II). ColM cytotoxicity is dependent on FkpA of the targeted cell, a chaperone with peptidylprolyl cis-trans isomerase activity. Dissection of ColM was used to delineate the catalytic domain and to identify the active-site residues. The in vitro activity of the isolated catalytic domain towards lipid II was 50-fold higher than that of the full-length bacteriocin. Moreover, this domain was bactericidal in the absence of FkpA under conditions that bypass the import mechanism (FhuA-TonB machinery). Thus ColM undergoes a maturation process driven by FkpA that is not required for the activity of the isolated catalytic domain. Genes encoding proteins with similarity to the catalytic domain of ColM were identified in pathogenic strains of Pseudomonas and other genera. ColM acts on several structures of lipid II representative of the diversity of peptidoglycan chemotypes. All together, these data open the way to the potential use of ColM-related bacteriocins as broad spectrum antibacterial agents.

MurJ is the flippase of lipid-linked precursors for peptidoglycan biogenesis

“…When added to E. coli , the protein toxin colicin M (ColM) is translocated into the periplasm where it cleaves lipid II (Fig. 1A) (11, 12). We therefore reasoned that ColM could be used in an assay to detect freshly flipped lipid II.…”

Structure and reconstitution of a hydrolase complex that releases peptidoglycan from the membrane after polymerization

“…8-10). 24,25 LC-MS analysis confirmed the presence of a diphosphate on a peptidoglycan fragment having an odd number of sugars, consistent with glucosaminidase cleavage to leave a terminal MurNAc (Supplementary Fig. 10).…”

“…10). Notably, SagB-SpdC’s cleavage activity in vitro depended on the conserved catalytic glutamate 13,26 13,26 13,25 13,25,20 in SagB (E155), but not on an SpdC residue conserved in eukaryotic CAAX proteases and required for their proteolytic activity (Supplementary Fig. 11).…”

Production of recombinant colicin M in Nicotiana tabacum plants and its antimicrobial activity

“…The molecular size of colicin M is about 29 kDa, which makes it one of the smallest among all known colicins. Its mechanism of action relies on hydrolyzing the phosphoester bond of the peptidoglycan lipid intermediate (Touzé et al 2012). This peptidoglycanase uses an FhuA receptor pathway to enter the susceptible cells (Kock et al 1987).…”