title: Distinguishing between different pathways of bilayer disruption by the related antimicrobial peptides cecropin B, B1 and B3.
abstract: Different pathways of bilayer disruption by the structurally related antimicrobial peptides cecropin B, B1 and B3, revealed by surface plasma resonance analysis of immobilized liposomes, differential scanning calorimetry of peptide-large unilamellar vesicle interactions, and light microscopic analysis of peptide-treated giant unilamellar vesicles, have been identified in this study. Natural cecropin B (CB) has one amphipathic and one hydrophobic alpha-helix, whereas cecropins B1 (CB1) and B3 (CB3), which are custom-designed, chimaeric analogues of CB, possess either two amphipathic or two hydrophobic alpha-helices, respectively. Surface plasma resonance analysis of unilamellar vesicles immobilized through a biotin-avidin interaction showed that both CB and CB1 bind to the lipid bilayers at high concentration (>10 microm); in contrast, CB3 induces disintegration of the vesicles at all concentrations tested. Differential scanning calorimetry showed the concentration-dependent effect of bilayer disruption, based on the different thermotrophic phase behaviours and the shapes of the thermal phase-transition curves obtained. The kinetics of the lysis of giant unilamellar vesicles observed by microscopy demonstrated that both CB and CB1 effect a continuous process involving loss of integrity followed by coalescence and resolution into smaller vesicles, whereas CB3 induces rapid formation of irregular-shaped, nonlamellar structures which rapidly disintegrate into twisted, microtubule-containing debris before being completely destroyed. On the basis of these observations, models by which CB, CB1 and CB3 induce lysis of lipid bilayers are discussed.
authors.affiliation: Institute of BioAgricultural Sciences, Academia Sinica, Taipei, Taiwan 115. robell@gate.sinica.edu.tw
authors.forename: Hueih Min
authors.initials: HM
authors.lastname: Chen
authors.forename: King Wong
authors.initials: KW
authors.lastname: Leung
authors.forename: Nagendra N
authors.initials: NN
authors.lastname: Thakur
authors.forename: Anmin
authors.initials: A
authors.lastname: Tan
authors.forename: Ralph W
authors.initials: RW
authors.lastname: Jack
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D019476:Insect Proteins / Q000737:chemistry / Q000494:pharmacology*; D008051:Lipid Bilayers; D008969:Molecular Sequence Data; D010455:Peptides; D020033:Protein Isoforms / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D019476:Insect Proteins; D008051:Lipid Bilayers; D010455:Peptides; D020033:Protein Isoforms; C031162:cecropin B protein, Insecta