European Biophysics Journal

, Volume 40, Issue 4, pp 515–528

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

  • Christof Junkes
  • Richard D. Harvey
  • Kenneth D. Bruce
  • Rudolf Dölling
  • Mojtaba Bagheri
  • Margitta Dathe
Original Paper

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.

Keywords

Antimicrobial Cyclic peptides Membrane permeabilisation Uptake Lipopolysaccharides 

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Copyright information

© European Biophysical Societies' Association 2011

Authors and Affiliations

  • Christof Junkes
    • 1
  • Richard D. Harvey
    • 2
  • Kenneth D. Bruce
    • 2
  • Rudolf Dölling
    • 3
  • Mojtaba Bagheri
    • 1
  • Margitta Dathe
    • 1
  1. 1.Leibniz Institute of Molecular Pharmacology (FMP)BerlinGermany
  2. 2.Institute of Pharmaceutical ScienceKing’s College LondonLondonUK
  3. 3.Biosyntan GmbHBerlinGermany

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