diphenylhexatriene and prodan

The ability of oligomeric lysozyme to modify the molecular organization of the model bilayer membranes composed of phosphatidylcholine (PC) and its mixtures with phosphatidylglycerol (PG) or cholesterol (Chol) was assessed using fluorescent probes 6-propionyl-2-dimethylaminonaphthalene (Prodan), 4-dimethylaminochalcone (DMC), pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH). The observed changes in the fluorescence characteristics of polarity-sensitive probes Prodan and DMC, located in interfacial bilayer region, were interpreted due to the partial dehydration of the glycerol backbone, which was under the influence of aggregated protein. Cholesterol was found to prevent the perturbations of membrane polar part by lysozyme aggregates. Analysis of the pyrene excimerization data revealed an oligomer-induced reduction in bilayer free volume, presumably caused by an increased packing density of hydrocarbon chains. This effect proved to be virtually independent of membrane composition. It was demonstrated that membranotropic activity of oligomeric lysozyme markedly exceeds that of monomeric protein. The biological significance of the results obtained is twofold, implicating the general membrane-mediated mechanisms of oligomer toxicity and specific pathways of lysozyme fibrillogenesis in vivo associated with familial nonneuropathic systemic amyloidosis.

Topics: 2-Naphthylamine; Chalcones; Cholesterol; Diphenylhexatriene; Fluorescent Dyes; Lipid Bilayers; Models, Molecular; Muramidase; Phosphatidylcholines; Polymers; Pyrenes; Spectrometry, Fluorescence

Ceramides (Cers) may exert their biological activity through changes in membrane structure and organization. To understand this mechanism, the effect of Cer on the biophysical properties of phosphatidylcholine, sphingomyelin (SM) and SM/cholesterol bilayers was determined using fluorescence probe techniques. The Cers were bovine brain Cer and synthetic Cers that contained a single acyl chain species. The phospholipids were 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glyero-3-phosphocholine (DPPC) and bovine brain, egg yolk and bovine erythrocyte SM. The addition of Cer to POPC and DPPC bilayers that were in the liquid-crystalline phase resulted in a linear increase in acyl chain order and decrease in membrane polarity. The addition of Cer to DPPC and SM bilayers also resulted in a linear increase in the gel to liquid-crystalline phase transition temperature (T(M)). The magnitude of the change was dependent upon Cer lipid composition and was much higher in SM bilayers than DPPC bilayers. The addition of 33 mol% cholesterol essentially eliminated the thermal transition of SM and SM/Cer bilayers. However, there is still a linear increase in acyl chain order induced by the addition of Cer. The results are interpreted as the formation of DPPC/Cer and SM/Cer lipid complexes. SM/Cer lipid complexes have higher T(M)s than the corresponding SM because the addition of Cer reduces the repulsion between the bulky headgroup and allows closer packing of the acyl chains. The biophysical properties of a SM/Cer-rich bilayer are dependent upon the amount of cholesterol present. In a cholesterol-poor membrane, a sphingomyelinase could catalyze the isothermal conversion of a liquid-crystalline SM bilayer to a gel phase SM/Cer complex at physiological temperature.

Topics: 2-Naphthylamine; Animals; Brain Chemistry; Cattle; Ceramides; Cholesterol; Diphenylhexatriene; Fluorescence Polarization; Laurates; Lipid Bilayers; Phosphatidylcholines; Signal Transduction; Sphingomyelins; Temperature

The reconstituted high density lipoproteins (rHDL) that were described in the preceding paper (Hefele Wald, J., Krul, E. S., and Jonas, A. (1990) J. Biol. Chem. 265, 20037-20043) are used in this study to analyze the organization, conformation, and dynamics of the lipid phase, as well as the relative orientation of the apolipoprotein alpha-helices and the lipid hydrocarbon chains. Two fluorescence polarization probes and a fluorescence polarity probe were used to detect the lipid phase transition behavior of the various particles, and to estimate the lipid order, mobility, and environment polarity in their gel and liquid-crystalline states. Infrared attenuated total reflection spectroscopy was used to estimate the content of secondary structure of the apolipoprotein, and the orientation of its alpha-helices with respect to the lipid hydrocarbon chains. In addition, the infrared spectra were analyzed in terms of the conformation and organization of different regions of the lipid molecules in the rHDL particles. The results indicate that the overall organization and conformation of lipid molecules in a lipid bilayer is preserved in the rHDL particles, but that progressive increases in apolipoprotein content straighten the hydrocarbon chains and decrease their packing order in the gel state, and decrease their mobility in the liquid-crystalline state. The presence of apolipoprotein also affects the conformation of the lipids at the level of the ester bonds and the head group of the phospholipid. In all three particle classes the content and distribution of secondary structures of the apolipoprotein were similar, and the alpha-helical segments were parallel to the lipid hydrocarbon chains.

Topics: 1,2-Dipalmitoylphosphatidylcholine; 2-Naphthylamine; Apolipoprotein A-I; Apolipoproteins A; Circular Dichroism; Diphenylhexatriene; Fluorescence Polarization; Fluorescent Dyes; Humans; Lipid Bilayers; Lipids; Lipoproteins, LDL; Protein Conformation; Spectrometry, Fluorescence; Spectrophotometry, Infrared