title: Dual mode of action of Bac7, a proline-rich antibacterial peptide.
abstract: Proline-rich peptides are a unique group of antimicrobial peptides that exert their activity selectively against Gram-negative bacteria through an apparently non-membranolytic mode of action that is not yet well understood. We have investigated the mechanism underlying the antibacterial activity of the proline-rich cathelicidin Bac7 against Salmonella enterica and Escherichia coli. The killing and membrane permeabilization kinetics as well as the cellular localization were assessed for the fully active N-terminal fragment Bac7(1-35), its all-D enantiomer and for differentially active shortened fragments. At sub-micromolar concentrations, Bac7(1-35) rapidly killed bacteria by a non-lytic, energy-dependent mechanism, whereas its D-enantiomer was inactive. Furthermore, while the L-enantiomer was rapidly internalized into bacterial cells, the D-enantiomer was virtually excluded. At higher concentrations (>or=64 microM), both L- and D-Bac7(1-35) were instead able to kill bacteria also via a lytic mechanism. Overall, these results suggest that Bac7 may inactivate bacteria via two different modes of action depending on its concentration: (i) at near-MIC concentrations via a mechanism based on a stereospecificity-dependent uptake that is likely followed by its binding to an intracellular target, and (ii) at concentrations several times the MIC value, via a non-stereoselective, membranolytic mechanism.
authors.affiliation: Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, Via Giorgieri 1, 34127 Trieste, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Podda
authors.forename: Monica
authors.initials: M
authors.lastname: Benincasa
authors.forename: Sabrina
authors.initials: S
authors.lastname: Pacor
authors.forename: Fulvio
authors.initials: F
authors.lastname: Micali
authors.forename: Maura
authors.initials: M
authors.lastname: Mattiuzzo
authors.forename: Renato
authors.initials: R
authors.lastname: Gennaro
authors.forename: Marco
authors.initials: M
authors.lastname: Scocchi
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000493:pharmacokinetics / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D005434:Flow Cytometry; D016253:Microscopy, Immunoelectron; D010599:Pharmacokinetics; D011392:Proline / Q000737:chemistry; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; C481640:Bac7(1-35) peptide; D011392:Proline