title: Solution structure and membrane interactions of the antimicrobial peptide fallaxidin 4.1a: an NMR and QCM study.
abstract: The solution structure of fallaxidin 4.1a, a C-terminal amidated analogue of fallaxidin 4.1, a cationic antimicrobial peptide isolated from the amphibian Litoria fallax, has been determined by nuclear magnetic resonance (NMR). In zwitterionic dodecylphosphocholine (DPC) micelles, fallaxidin 4.1a adopted a partially helical structure with random coil characteristics. The flexibility of the structure may enhance the binding and penetration upon interaction with microbial membranes. Solid-state (31)P and (2)H NMR was used to investigate the effects of fallaxidin 4.1a on the dynamics of phospholipid membranes, using acyl chain deuterated zwitterionic dimyristoylphosphatidylcholine (DMPC-d(54)) and anionic dimyristoylphosphatidylglycerol (DMPG) multilamellar vesicles. In DMPC-d(54) vesicle bilayers, fallaxidin 4.1a caused a decrease in the (31)P chemical shift anisotropy (CSA), and a decrease in deuterium order parameters from the upper acyl chain region, indicating increased lipid motion about the phosphate headgroups. Conversely, for DMPC-d(54)/DMPG, two (31)P CSA were observed due to a lateral phase separation of the two lipids and/or differing headgroup orientations in the presence of fallaxidin 4.1a, with a preferential interaction with DMPG. Little effect on the deuterated acyl chain order parameters was observed in the d(54)-DMPC/DMPG model membranes. Real time quartz crystal microbalance analyses of fallaxidin 4.1a addition to DMPC and DMPC/DMPG supported lipid bilayers together with the NMR results indicated transmembrane pore formation in DMPC/DMPG membranes and peptide insertion followed by disruption at a threshold concentration in DMPC membranes. The different interactions observed with "mammalian" (DMPC) and "bacterial" (DMPC/DMPG) model membranes imply fallaxidin 4.1a may be a useful antimicrobial peptide, with preferential cytolytic activity toward prokaryotic organisms at low peptide concentrations (<5 microM).
authors.affiliation: Department of Chemistry, The University of Adelaide, South Australia 5005, Australia.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Sherman
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Jackway
authors.forename: John D
authors.initials: JD
authors.lastname: Gehman
authors.forename: Slavica
authors.initials: S
authors.lastname: Praporski
authors.forename: George A
authors.initials: GA
authors.lastname: McCubbin
authors.forename: Adam
authors.initials: A
authors.lastname: Mechler
authors.forename: Lisandra L
authors.initials: LL
authors.lastname: Martin
authors.forename: Frances
authors.initials: F
authors.lastname: Separovic
authors.forename: John H
authors.initials: JH
authors.lastname: Bowie
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D001001:Anura / Q000382:microbiology*; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism / Q000382:microbiology*; D003460:Crystallization; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry* / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000254:growth & development; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011791:Quartz; D012996:Solutions
chemical_list: D023181:Antimicrobial Cationic Peptides; D008051:Lipid Bilayers; D012996:Solutions; C533569:fallaxidin 4.1, Litoria fallax; D011791:Quartz; D004134:Dimyristoylphosphatidylcholine