title: Interaction of gramicidin with DPPC/DODAB bilayer fragments.
abstract: The interaction between the antimicrobial peptide gramicidin (Gr) and dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB) 1:1 large unilamellar vesicles (LVs) or bilayer fragments (BFs) was evaluated by means of several techniques. The major methods were: 1) Gr intrinsic fluorescence and circular dichroism (CD) spectroscopy; 2) dynamic light scattering for sizing and zeta-potential analysis; 3) determination of the bilayer phase transition from extrinsic fluorescence of bilayer probes; 4) pictures of the dispersions for evaluation of coloidal stability over a range of time and NaCl concentration. For Gr in LVs, the Gr dimeric channel conformation is suggested from: 1) CD and intrinsic fluorescence spectra similar to those in trifluoroethanol (TFE); 2) KCl or glucose permeation through the LVs/Gr bilayer. For Gr in BFs, the intertwined dimeric, non-channel Gr conformation is evidenced by CD and intrinsic fluorescence spectra similar to those in ethanol. Both LVs and BFs shield Gr tryptophans against quenching by acrylamide but the Stern-Volmer quenching constant was slightly higher for Gr in BFs confirming that the peptide is more exposed to the water phase in BFs than in LVs. The DPPC/DODAB/Gr supramolecular assemblies may predict the behavior of other antimicrobial peptides in assemblies with lipids.
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05513-970, São Paulo, SP, Brazil.
authors.forename: Camilla A
authors.initials: CA
authors.lastname: Carvalho
authors.forename: Constanza
authors.initials: C
authors.lastname: Olivares-Ortega
authors.forename: Marco A
authors.initials: MA
authors.lastname: Soto-Arriaza
authors.forename: Ana M
authors.initials: AM
authors.lastname: Carmona-Ribeiro
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry / Q000378:metabolism*; D006096:Gramicidin / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008055:Lipids / Q000737:chemistry; D008968:Molecular Conformation; D044367:Phase Transition; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D000644:Quaternary Ammonium Compounds; D006096:Gramicidin; C015831:dimethyldioctadecylammonium; D015060:1,2-Dipalmitoylphosphatidylcholine