Résumé
Microcins are low-molecular-weight antibacterial peptides secreted by enterobacteria. Microcin E492 (MccE492) was isolated from Klebsiella pneumoniae RYC492 or the recombinant E. coli VCS257 harboring the pJAM229 plasmid as a hydrophobic and anionic 84-residue unmodified peptide of molecular mass 7886 Da. As a membrane-active peptide, MccE492 depolarizes the cytoplasmic membrane of E. coli. However, this membrane activity alone cannot account for the peptide bactericidal activity, which is thought to involve a receptor-mediated mechanism. We have isolated a posttranslationally modified form of MccE492 (MccE492m) with more potent antimicrobial properties than MccE492. We determined the structure of this posttranslational modification and identified the membrane receptors involved in the microcin recognition at the outer membrane of the sensitive strains. MccE492m is the first example of a novel type of antibacterial peptides that we call siderophore-peptides.