title: Studies on lactoferricin-derived Escherichia coli membrane-active peptides reveal differences in the mechanism of N-acylated versus nonacylated peptides.
abstract: To improve the low antimicrobial activity of LF11, an 11-mer peptide derived from human lactoferricin, mutant sequences were designed based on the defined structure of LF11 in the lipidic environment. Thus, deletion of noncharged polar residues and strengthening of the hydrophobic N-terminal part upon adding a bulky hydrophobic amino acid or N-acylation resulted in enhanced antimicrobial activity against Escherichia coli, which correlated with the peptides' degree of perturbation of bacterial membrane mimics. Nonacylated and N-acylated peptides exhibited different effects at a molecular level. Nonacylated peptides induced segregation of peptide-enriched and peptide-poor lipid domains in negatively charged bilayers, although N-acylated peptides formed small heterogeneous domains resulting in a higher degree of packing defects. Additionally, only N-acylated peptides perturbed the lateral packing of neutral lipids and exhibited increased permeability of E. coli lipid vesicles. The latter did not correlate with the extent of improvement of the antimicrobial activity, which could be explained by the fact that elevated binding of N-acylated peptides to lipopolysaccharides of the outer membrane of gram-negative bacteria seems to counteract the elevated membrane permeabilization, reflected in the respective minimal inhibitory concentration for E. coli. The antimicrobial activity of the peptides correlated with an increase of membrane curvature stress and hence bilayer instability. Transmission electron microscopy revealed that only the N-acylated peptides induced tubular protrusions from the outer membrane, whereas all peptides caused detachment of the outer and inner membrane of E. coli bacteria. Viability tests demonstrated that these bacteria were dead before onset of visible cell lysis.
authors.affiliation: Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Zweytick
authors.forename: Günter
authors.initials: G
authors.lastname: Deutsch
authors.forename: Jörg
authors.initials: J
authors.lastname: Andrä
authors.forename: Sylvie E
authors.initials: SE
authors.lastname: Blondelle
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Vollmer
authors.forename: Roman
authors.initials: R
authors.lastname: Jerala
authors.forename: Karl
authors.initials: K
authors.lastname: Lohner
mesh_terms: D000215:Acylation; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D001703:Biophysics / Q000379:methods; D002152:Calorimetry, Differential Scanning / Q000379:methods; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D007781:Lactoferrin / Q000737:chemistry*; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry; D046529:Microscopy, Electron, Transmission / Q000379:methods; D010455:Peptides / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry; D017434:Protein Structure, Tertiary
chemical_list: D023181:Antimicrobial Cationic Peptides; D008081:Liposomes; D010455:Peptides; D010743:Phospholipids; C082171:lactoferricin B; D007781:Lactoferrin