title: Direct comparison of membrane interactions of model peptides composed of only Leu and Lys residues.
abstract: We compared the properties of two peptides of identical size and amino acid composition, Ac-(LKKL)(5)-NHEt and Ac-(KL)(10)-NHEt. Both are amphipathic, but only Ac-(LKKL)(5)-NHEt is a potent promoter of negative curvature. CD studies performed in the presence of lipids confirmed that under these conditions Ac-(LKKL)(5)-NHEt forms an alpha-helix, and Ac-(KL)(10)-NHEt adopts a beta structure. We studied their binding affinity by centrifugation and isothermal titration calorimetry techniques. The Ac-(LKKL)(5)-NHEt bound to zwitterionic and anionic liposomes, while Ac-(KL)(10)-NHEt interacted mainly with anionic liposomes. Ac-(LKKL)(5)-NHEt was more lytic than Ac-(KL)(10)-NHEt for zwitterionic palmitoyloleoylphosphatidylcholine (POPC) liposomes, and for liposomes composed of lipids extracted from either sheep or human erythrocytes (RBC). Both peptides had similar lytic and lipid mixing activities for liposomes containing anionic lipids. Both peptides were highly hemolytic, with Ac-(LKKL)(5)-NHEt active against sheep RBC and Ac-(KL)(10)-NHEt more active against human RBC. From their respective minimal effective concentrations (MECs) as antimicrobial agents, we judged Ac-(KL)(10)-NHEt to be 2 to 5-fold more potent than Ac-(LKKL)(5)-NHEt in media that contained physiological concentrations of NaCl. Notwithstanding, both peptides had MECs <1 microg/mL for Escherichia coli and Pseudomonas aeruginosa and <4 microg/mL for Staphylococcus aureus and methicillin-resistant Staphylococcus aureus. Although selectivity of antimicrobial peptides for bacterial membranes may result, in part, from the preferential display of anionic residues in these membranes, inability to interact with or bind to zwitterionic phospholipids offers no guarantee that the peptide will lack appreciable cytotoxicity for host cells.
authors.affiliation: Department of Biochemistry, McMaster University, Hamilton, ON L8N 3Z5, Canada.
authors.forename: Raquel F
authors.initials: RF
authors.lastname: Epand
authors.forename: Robert I
authors.initials: RI
authors.lastname: Lehrer
authors.forename: Alan
authors.initials: A
authors.lastname: Waring
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Régine
authors.initials: R
authors.lastname: Maget-Dana
authors.forename: Dominique
authors.initials: D
authors.lastname: Lelièvre
authors.forename: Richard M
authors.initials: RM
authors.lastname: Epand
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry / Q000494:pharmacology; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D007930:Leucine; D008081:Liposomes / Q000737:chemistry*; D008239:Lysine; D008561:Membrane Fusion; D008567:Membranes, Artificial; D008954:Models, Biological; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D000890:Anti-Infective Agents; D008081:Liposomes; D008567:Membranes, Artificial; D009842:Oligopeptides; D010455:Peptides; D007930:Leucine; D008239:Lysine