title: Cyclic antimicrobial R-, W-rich peptides: the role of peptide structure and E. coli outer and inner membranes in activity and the mode of action.
abstract: This study compares the effect of cyclic R-, W-rich peptides with variations in amino acid sequences and sizes from 5 to 12 residues upon Gram negative and Gram positive bacteria as well as outer membrane-deficient and LPS mutant Escherichia coli (E. coli) strains to analyze the structural determinants of peptide activity. Cyclo-RRRWFW (c-WFW) was the most active and E. coli-selective sequence and bactericidal at the minimal inhibitory concentration (MIC). Removal of the outer membrane distinctly reduced peptide activity and the complete smooth LPS was required for maximal activity. c-WFW efficiently permeabilised the outer membrane of E. coli and promoted outer membrane substrate transport. Isothermal titration calorimetric studies with lipid A-, rough-LPS (r-LPS)- and smooth-LPS (s-LPS)-doped POPC liposomes demonstrated the decisive role of O-antigen and outer core polysaccharides for peptide binding and partitioning. Peptide activity against the inner E. coli membrane (IM) was very low. Even at a peptide to lipid ratio of 8/1, c-WFW was not able to permeabilise a phosphatidylglycerol/phosphatidylethanolamine (POPG/POPE) bilayer. Low influx of propidium iodide (PI) into bacteria confirmed a low permeabilising ability of c-WFW against PE-rich membranes at the MIC. Whilst the peptide effect upon eukaryotic cells correlated with the amphipathicity and permeabilisation of neutral phosphatidylcholine bilayers, suggesting a membrane disturbing mode of action, membrane permeabilisation does not seem to be the dominating antimicrobial mechanism of c-WFW. Peptide interactions with the LPS sugar moieties certainly modulate the transport across the outer membrane and are the basis of the E. coli selectivity of this type of peptides.
authors.affiliation: Leibniz Institute of Molecular Pharmacology (FMP), Robert-Roessle-Str. 10, 13125 Berlin, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Junkes
authors.forename: Richard D
authors.initials: RD
authors.lastname: Harvey
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Bruce
authors.forename: Rudolf
authors.initials: R
authors.lastname: Dölling
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Bagheri
authors.forename: Margitta
authors.initials: M
authors.lastname: Dathe
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000737:chemistry / Q000494:pharmacology*; D002151:Calorimetry; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000737:chemistry / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry / Q000494:pharmacology*; D010714:Phosphatidylethanolamines / Q000737:chemistry / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000737:chemistry / Q000378:metabolism
chemical_list: D000890:Anti-Infective Agents; D008070:Lipopolysaccharides; D008081:Liposomes; D010456:Peptides, Cyclic; D010714:Phosphatidylethanolamines; D010715:Phosphatidylglycerols; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine