title: Microcin E492 antibacterial activity: evidence for a TonB-dependent inner membrane permeabilization on Escherichia coli.
abstract: The mechanism of action of microcin E492 (MccE492) was investigated for the first time in live bacteria. MccE492 was expressed and purified to homogeneity through an optimized large-scale procedure. Highly purified MccE492 showed potent antibacterial activity at minimal inhibitory concentrations in the range of 0.02-1.2 microM. The microcin bactericidal spectrum of activity was found to be restricted to Enterobacteriaceae and specifically directed against Escherichia and Salmonella species. Isogenic bacteria that possessed mutations in membrane proteins, particularly of the TonB-ExbB-ExbD complex, were assayed. The microcin bactericidal activity was shown to be TonB- and energy-dependent, supporting the hypothesis that the mechanism of action is receptor mediated. In addition, MccE492 depolarized and permeabilized the E. coli cytoplasmic membrane. The membrane depolarization was TonB dependent. From this study, we propose that MccE492 is recognized by iron-siderophore receptors, including FepA, which promote its import across the outer membrane via a TonB- and energy-dependent pathway. MccE492 then inserts into the inner membrane, whereupon the potential becomes destabilized by pore formation. Because cytoplasmic membrane permeabilization of MccE492 occurs beneath the threshold of the bactericidal concentration and does not result in cell lysis, the cytoplasmic membrane is not hypothesized to be the sole target of MccE492.
authors.affiliation: Chimie et Biochimie des Substances Naturelles, ESA 8041 CNRS, USM 502 Muséum National d'Histoire Naturelle, Paris, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Destoumieux-Garzón
authors.forename: Xavier
authors.initials: X
authors.lastname: Thomas
authors.forename: Mónica
authors.initials: M
authors.lastname: Santamaria
authors.forename: Christophe
authors.initials: C
authors.lastname: Goulard
authors.forename: Michel
authors.initials: M
authors.lastname: Barthélémy
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Boscher
authors.forename: Yannick
authors.initials: Y
authors.lastname: Bessin
authors.forename: Gérard
authors.initials: G
authors.lastname: Molle
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Pons
authors.forename: Lucienne
authors.initials: L
authors.lastname: Letellier
authors.forename: Jean
authors.initials: J
authors.lastname: Peduzzi
authors.forename: Sylvie
authors.initials: S
authors.lastname: Rebuffat
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001430:Bacteriocins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology / Q000378:metabolism; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism*; D010455:Peptides; D010539:Permeability; D011487:Protein Conformation; D059005:Topoisomerase II Inhibitors
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001430:Bacteriocins; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010455:Peptides; D059005:Topoisomerase II Inhibitors; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; C020411:microcin