title: The interaction of arginine- and tryptophan-rich cyclic hexapeptides with Escherichia coli membranes.
abstract: Cyclization of R- and W-rich hexapeptides has been found to enhance specifically the antimicrobial activity against Gram-negative Escherichia coli. To gain insight into the role of the bacterial outer membrane in mediating selectivity, we assayed the activity of cyclic hexapeptides derived from the parent sequence c-(RRWWRF) against several E. coli strains and Bacillus subtilis, L-form bacteria, and E. coli lipopolysaccharide (LPS) mutant strains, and we also investigated the peptide-induced permeabilization of the outer and inner membrane of E. coli. Wall-deficient L-form bacteria were distinctly less susceptible than the wild type strain. The patterns of peptide-induced permeabilization of the outer and inner E. coli membranes correlated well with the antimicrobial activity, confirming that membrane permeabilization is a detrimental effect of the peptides upon bacteria. Truncation of LPS had no influence on the activity of the cyclic parent peptide, but the highly active c-(RRWFWR), with three adjacent aromatic residues, required the complete LPS for maximal activity. Furthermore, differences in the activity of the parent peptide and its all-D sequence indicated stereospecific interactions with the LPS mutant strains. We suggest that, depending on the primary sequence of the peptides, either hydrophobic interactions with the fatty acid chains of lipid A, or electrostatic interactions disturbing the polar core region and interference with saccharide-saccharide interactions prevail in the barrier-disturbing effect upon the outer membrane and thereby provide peptide accessibility to the inner membrane. The results underline the importance of tryptophan and arginine residues and their relative location for a high antimicrobial effect, and the activity-modulating function of the outer membrane of E. coli. In addition to membrane permeabilization, the data provided evidence for the involvement of other mechanisms in growth inhibition and killing of bacteria.
authors.affiliation: Leibniz Institute of Molecular Pharmacology, Robert-Rössle-Str. 10, 13125 Berlin, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Junkes
authors.forename: Axel
authors.initials: A
authors.lastname: Wessolowski
authors.forename: Sebastien
authors.initials: S
authors.lastname: Farnaud
authors.forename: Robert W
authors.initials: RW
authors.lastname: Evans
authors.forename: Liam
authors.initials: L
authors.lastname: Good
authors.forename: Michael
authors.initials: M
authors.lastname: Bienert
authors.forename: Margitta
authors.initials: M
authors.lastname: Dathe
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D020128:Inhibitory Concentration 50; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D009842:Oligopeptides / Q000737:chemistry* / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013997:Time Factors; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D023181:Antimicrobial Cationic Peptides; D009842:Oligopeptides; D010456:Peptides, Cyclic; D014364:Tryptophan; D000409:Alanine