title: Influence of tryptophan on lipid binding of linear amphipathic cationic antimicrobial peptides.
abstract: We recently demonstrated that a linear 18-residue peptide, (KIGAKI)(3)-NH(2), designed to form amphipathic beta-sheet structure when bound to lipid bilayers, possessed potent antimicrobial activity and low hemolytic activity. The ability of (KIGAKI)(3)-NH(2) to induce leakage from lipid vesicles was compared to that of the amphipathic alpha-helical peptide, (KIAGKIA)(3)-NH(2), which had equivalent antimicrobial activity. Significantly, the lytic properties of (KIGAKI)(3)-NH(2) were enhanced for mixed acidic-neutral lipid vesicles containing phosphatidylethanolamine instead of phosphatidylcholine as the neutral component, while the potency of (KIAGKIA)(3)-NH(2) was significantly reduced [Blazyk, J., et al. (2001) J. Biol. Chem. 276, 27899-27906]. In this paper, we measured the lytic properties of these peptides, as well as several fluorescent analogues containing a single tryptophan residue, by monitoring permeability changes in large unilamellar vesicles with varying lipid compositions and in Escherichia coli cells. The binding of these peptides to lipid bilayers with defined compositions was compared using surface plasmon resonance, circular dichroism, and fluorescence spectroscopy. Surprisingly large differences were observed in membrane binding properties, particularly in the case of KIGAKIKWGAKIKIGAKI-NH(2). Since all of these peptides possess the same charge and very similar mean hydrophobicities, the binding data cannot be explained merely in terms of electrostatic and/or hydrophobic interactions. In light of their equivalent antimicrobial and hemolytic potencies, some of these peptides may employ mechanisms beyond simply increasing plasma membrane permeability to exert their lethal effects.
authors.affiliation: Department of Chemistry, College of Arts and Sciences, Ohio University, Athens, Ohio 45701, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Jin
authors.forename: Henriette
authors.initials: H
authors.lastname: Mozsolits
authors.forename: Janet
authors.initials: J
authors.lastname: Hammer
authors.forename: Erik
authors.initials: E
authors.lastname: Zmuda
authors.forename: Fang
authors.initials: F
authors.lastname: Zhu
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Marie Isabel
authors.initials: MI
authors.lastname: Aguilar
authors.forename: Jack
authors.initials: J
authors.lastname: Blazyk
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism; D001419:Bacteria / Q000187:drug effects*; D002942:Circular Dichroism; D004912:Erythrocytes / Q000378:metabolism; D005452:Fluoresceins / Q000378:metabolism; D006461:Hemolysis; D006801:Humans; D008969:Molecular Sequence Data; D009598:Nitrophenylgalactosides / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism*; D010715:Phosphatidylglycerols / Q000378:metabolism*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D020349:Surface Plasmon Resonance; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D005452:Fluoresceins; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; C055012:2-nitrophenylgalactoside; D009598:Nitrophenylgalactosides; D014364:Tryptophan; C007740:fluorexon