title: Membrane interactions of designed cationic antimicrobial peptides: the two thresholds.
abstract: Novel cationic antimicrobial peptides (CAPs) designed in our lab-typified by sequences such as KKKKKKAAX-AAXAAXAA-NH(2), where X = Phe/Trp-display high antibacterial activity but exhibit little or no hemolytic activity towards human red blood cells even at high doses. To clarify the mechanism of their selectivity for bacterial versus mammalian membranes and to increase our understanding of the relationships between primary sequence and bioactivity, a library of derivatives was prepared by increasing segmental hydrophobicity, in which systematic substitutions of Ala for two, three, or four Leu residues were made. Conformationally constrained dimeric and cyclic derivatives were also synthesized. The peptides were examined for activity against pathogenic bacteria (Pseudomonas aeruginosa), hemolytic activity on human red blood cells, and insertion into models of natural bacterial membranes (containing anionic lipids) and mammalian membranes (containing zwitterionic lipids + cholesterol). Results were compared with corresponding properties of the natural CAPs magainin and cecropin. Using circular dichroism and fluorescence spectroscopy, we found that peptide conformation and membrane insertion were sequence dependent, both upon the number of Leu residues, and upon their positions along the hydrophobic core. Membrane disruption was likely enhanced by the fact that the peptides contain potent dimerization-promoting sequence motifs, as assessed by SDS-PAGE gel analysis. The overall results led us to identify distinctions in the mechanism of actions of these CAPs for disruption of bacterial versus mammalian membranes, the latter dependent on surpassing a "second hydrophobicity threshold" for insertion into zwitterionic membranes.
authors.affiliation: Division of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Evgenia
authors.initials: E
authors.lastname: Glukhov
authors.forename: Lori L
authors.initials: LL
authors.lastname: Burrows
authors.forename: Charles M
authors.initials: CM
authors.lastname: Deber
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D002462:Cell Membrane / Q000737:chemistry* / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D004912:Erythrocytes / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides