Résumé
The mechanism of action of microcin E492, the antimicrobial peptide from Klebsiella pneumoniae was investigated and compared to that of the more potent MccE492m, a recently isolated posttranslationally modified form of MccE492. In vitro, both peptides formed ion-channels in planar lipid bilayers. In vivo, they depolarized and permeabilized the cytoplasmic membrane of E. coli. Both the antibacterial and membrane activities of the peptides were TonB- and energy-dependent. The receptors for MccE492 and MccE492m were identified by assaying their antibacterial activity against isogenic bacteria possessing mutations in outer membrane proteins known as receptors for the 2,3-dihydroxybenzoylserine (DHBS) catechol type siderophore. Two of them, FepA and Fiu, are required for the MccE492 and MccE492m activity, while Cir has an accessory role. Since the MccE492m posttranslational modification contains DHBS, we propose that improvement of MccE492 activity upon modification would result from an increase of the microcin/receptor affinity.