title: Membrane association and contact formation by a synthetic analogue of polymyxin B and its fluorescent derivatives.
abstract: sP-B is a synthetic analogue of the natural lipopeptide antibiotic polymyxin B (PxB) that maintains the ability of the parent compound to form vesicle-vesicle contacts and induce lipid exchange. Exchange is selective, and only monoanionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphoglycerol (POPG) are transferred, whereas dianionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphate (POPA) are not, as shown by fluorescence experiments based on the excimer/monomer ratio of pyrene-labeled phospholipids. Synthetic fluorescent analogues of sP-B are used to investigate the peptide position and orientation in the intermembrane contacts: sP-Bw, an analogue that contains D-tryptophan (D-Trp) instead of the naturally occurring D-phenylalanine, and sP-Bpy, incorporating a pyrene group at the N-terminus. Tryptophan fluorescence, anisotropy, and quenching measurements performed with sP-Bw indicate that the peptide binds and inserts in anionic vesicles of POPG and POPA. However, significant differences are seen depending on the lipid composition, as also demonstrated by fluorescence resonance energy transfer (FRET) experiments from Trp to 7-nitro-2-1,3-benzoxadiazol (NBD) groups at the interface. Intermolecular FRET using sP-Bw as the donor and sP-Bpy as the acceptor indicates self-association of the peptide, possibly forming dimers, when bound to POPG vesicles at concentrations that induce the vesicle-vesicle contacts.
authors.affiliation: Physical Chemistry Department, Faculty of Pharmacy, University of Barcelona, Avn. Joan XXIII s/n, 08028 Barcelona, Spain.
authors.forename: Adrià
authors.initials: A
authors.lastname: Clausell
authors.forename: Francesc
authors.initials: F
authors.lastname: Rabanal
authors.forename: Maria
authors.initials: M
authors.lastname: Garcia-Subirats
authors.forename: M
authors.initials: M
authors.lastname: Asunción Alsina
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Cajal
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry; D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D008055:Lipids / Q000737:chemistry; D011112:Polymyxin B / Q000031:analogs & derivatives* / Q000737:chemistry*; D011485:Protein Binding; D053835:Unilamellar Liposomes / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D008055:Lipids; D053835:Unilamellar Liposomes; C521624:sP-B compound; C521625:sP-Bpy compound; C521623:sP-Bw compound; D011112:Polymyxin B