title: Detection of membrane packing defects by time-resolved fluorescence depolarization.
abstract: Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers.
authors.affiliation: Department of Physics, Texas Tech University, Lubbock 79409-1051, USA.
authors.forename: S Y
authors.initials: SY
authors.lastname: Chen
authors.forename: K H
authors.initials: KH
authors.lastname: Cheng
mesh_terms: D002462:Cell Membrane / Q000502:physiology*; D004058:Diffusion; D007700:Kinetics; D008051:Lipid Bilayers; D008433:Mathematics; D008954:Models, Biological; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D013050:Spectrometry, Fluorescence / Q000379:methods; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C038191:1,2-dilinoleoyl-3-phosphatidylethanolamine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine