dioleoyl-phosphatidylethanolamine and 1-2-dipalmitoyl-3-phosphatidylethanolamine

Because transmembrane proteins (TMPs) can be obtained with sufficient purity for X-ray diffraction studies more frequently than decades ago, their mechanisms of action may now be elucidated. One of the pending issues is the actual interplay between transmembrane proteins and membrane lipids. There is strong evidence of the involvement of specific lipids with some membrane proteins, such as the potassium crystallographically sited activation channel (KcsA) of Streptomyces lividans and the secondary transporter of lactose LacY of Escherichia coli, the activities of which are associated with the presence of anionic phospholipids such as the phosphatidylglycerol (PG) and phosphatidyethanolamine (PE), respectively. Other proteins such as the large conductance mechanosensitive channel (MscL) of E. coli seem to depend on the adaptation of specific phospholipids to the irregular surface of the integral membrane protein. In this work we investigated the lateral compressibility of two homoacid phosphatidylethanolamines (one with both acyl chains unsaturated (DOPE), the other with the acyl chains saturated (DPPE)) and the heteroacid phosphatidyletanolamine (POPE) and their mixtures with POPG. The liquid expanded (LE) to liquid condensed (LC) transition was observed in POPE at a temperature below its critical temperature (T

Topics: Bacterial Proteins; Compressive Strength; Escherichia coli; Escherichia coli Proteins; Ion Channels; Microscopy, Atomic Force; Monosaccharide Transport Proteins; Phosphatidylethanolamines; Potassium Channels; Streptomyces lividans; Symporters; Temperature; Thermodynamics; Unilamellar Liposomes

The fusion of lipid membranes is a key process in biology. It enables cells and organelles to exchange molecules with their surroundings, which otherwise could not cross the membrane barrier. To study such complex processes we use simplified artificial model systems, i.e., an optical fusion assay based on membrane-coated glass spheres. We present a technique to analyze membrane-membrane interactions in a large ensemble of particles. Detailed information on the geometry of the fusion stalk of fully fused membranes is obtained by studying the diffusional lipid dynamics with fluorescence recovery after photobleaching experiments. A small contact zone is a strong obstruction for the particle exchange across the fusion spot. With the aid of computer simulations, fluorescence-recovery-after-photobleaching recovery times of both fused and single-membrane-coated beads allow us to estimate the size of the contact zones between two membrane-coated beads. Minimizing delamination and bending energy leads to minimal angles close to those geometrically allowed.

Topics: Algorithms; Cell Fusion; Computer Simulation; Diffusion; Fluorescence Recovery After Photobleaching; Fluorescent Dyes; Glass; Heterocyclic Compounds, 4 or More Rings; Lipopeptides; Membrane Fusion; Membranes, Artificial; Microscopy, Confocal; Models, Theoretical; Phosphatidylcholines; Phosphatidylethanolamines; Silicon Dioxide; Xanthenes

To understand the relationship between the chemical structure of polar molecules and their membrane location, the behavior of dansyl (dimethylaminonaphthalenesulfonyl) and related polar fluorescent probes was examined. The depth of these probes in lipid bilayers was determined by parallax analysis of fluorescence quenching [Chattopadhyay and London (1987) Biochemistry 26, 39-45; Abrams & London, Biochemistry (1993) 32, 10826-10831]. Quenching was measured for dansyl groups: (1) attached to the polar headgroup of PE, (2) linked to an alkyl chain, (3) attached to the end of a fatty acyl chain, and (4) attached to the polar headgroup of PE via a spacer group. In all cases, the dansyl probes located in the polar headgroup region, 19-21 A from the bilayer center. This shows the dansyl group has a strong tendency to seek a shallow location in the polar headgroup region. The only exception to this pattern was in the case of a dialkylated dansyl, for which two populations were observed. One population was at the polar headgroup level, but the second was deeply buried in the acyl chain region. To see if the polar sulfonamide group of dansyl influences depth, a structurally related probe substituting a thiocarbamoyl linkage, dimethylaminonaphthalenethiocarbamoyl (dantyl)-labeled PE, was synthesized. Dantyl groups were located deeper than dansyl groups, 13-16 A from the bilayer center. There was an even more dramatic difference in depth between dansyl and mansyl (methylanilinonaphthalenesulfonyl) derivatives. Mansyl probes, which have an extra phenyl group relative to dansyl, were found to locate deeply within the acyl chain region of the bilayer (6-7 A from the bilayer center) when attached to the polar headgroup of PE. Thus, the membrane location of polar groups depends strongly on the details of their chemical structure, and it is possible for a polar group to locate both at shallow and deep locations. These results suggest the energy to bury a polar moiety in the hydrophobic part of the bilayer is not prohibitively high. This contrasts to the behavior of charged groups, which appear to be restricted to shallow locations in membranes. In this report, the effect of populations at two different depths on the parallax analysis is also considered.

Topics: Dansyl Compounds; Fluorescent Dyes; Lipid Bilayers; Membrane Lipids; Membranes; Phosphatidylethanolamines; Spectrometry, Fluorescence

1. The effect of liposome phospholipid composition has been assumed to be relatively unimportant because of the presumed inert nature of phospholipids. 2. We have previously shown that cationic liposome formulations used for gene therapy inhibit, through their cationic component, the synthesis by activated macrophages of the pro-inflammatory mediators nitric oxide (NO) and tumour necrosis factor-alpha (TNF-alpha). 3. In this study, we have evaluated the ability of different cationic lipids to reduce footpad inflammation induced by carrageenan and by sheep red blood cell challenge. 4. Parenteral (i.p. or s.c) or local injection of the positively charged lipids dimethyldioctadecylammomium bromide (DDAB), dioleyoltrimethylammonium propane (DOTAP), dimyristoyltrimethylammonium propane (DMTAP) or dimethylaminoethanecarbamoyl cholesterol (DC-Chol) significantly reduced the inflammation observed in both models in a dose-dependent manner (maximum inhibition: 70-95%). 5. Cationic lipids associated with dioleyol- or dipalmitoyl-phosphatidylethanolamine retained their anti-inflammatory activity while cationic lipids associated with dipalmitoylphosphatidylcholine (DPPC) or dimyristoylphosphatidylglycerol (DMPG) showed no anti-inflammatory activity, indicating that the release of cationic lipids into the macrophage cytoplasm is a necessary step for anti-inflammatory activity. The anti-inflammatory activity of cationic lipids was abrogated by the addition of dipalmitoylphosphatidylethanolamine-poly(ethylene)glycol-2000 (DPPE-PEG2000) which blocks the interaction of cationic lipids with macrophages. 6. Because of the significant role of protein kinase C (PKC) in the inflammatory process we have determined whether the cationic lipids used in this study inhibit PKC activity. The cationic lipids significantly inhibited the activity of PKC but not the activity of a non-related protein kinase, PKA. The synthesis of interleukin-6 (IL-6), which is not dependent on PKC activity for its induction in macrophages, was not modified in vitro or in situ by cationic lipids. The synthesis of NO and TNF-alpha in macrophages, both of which are PKC-dependent, was downregulated by cationic lipids. 7. These results demonstrate that cationic lipids can be considered as novel anti-inflammatory agents. The downregulation of pro-inflammatory mediators through interaction of cationic lipids with the PKC pathway may explain this anti-inflammatory activity. Furthermore, since cationic lipids have

Topics: Animals; Anti-Inflammatory Agents; Carrageenan; Cations; Cholesterol; Edema; Erythrocytes; Fatty Acids, Monounsaturated; Female; Liposomes; Mice; Phosphatidylethanolamines; Phospholipids; Protein Kinase C; Quaternary Ammonium Compounds; Sheep

A multivalent ligand system, in which enkephalin/phospholipid conjugates were immobilized on a polymerized liposome, has been prepared. A hydrophilic spacer chain, -(Sar-Sar-Pro)2-, was placed between Tyr-D-Ala-Gly-Trp-Leu (an enkephalin part) and a phospholipid part to diminish steric hindrance of the liposome against receptor binding of the enkephalin unit. The affinity of the immobilized enkephalin conjugate for opioid receptor was dependent on the density of the enkephalin unit on the surface of polymerized liposome, indicating that more than two enkephalin units on a liposome simultaneously bind to receptors in the membrane. IC50 values for the delta- and mu-receptors were 15 and 26 nM, respectively, when the conjugate was immobilized at the molar ratio of [enkephalin]/[phospholipid] of 340. The latter affinity is better than that of Tyr-D-Ala-Gly-Trp-Leu (50 nM). The enkephalin part was located at the membrane surface, as indicated by fluorescence spectroscopy. When 12% cerebroside sulfate was mixed in the polymerized liposome, delta-receptor affinity of the immobilized enkephalin conjugate was improved to 7.4 nM. The environment around the enkephalin part became hydrophilic upon incorporation of cerebroside sulfate into the polymerized liposome, resulting in changes in the receptor affinities.

Topics: Animals; Cattle; Drug Carriers; Drug Design; Enkephalins; Ligands; Lipids; Liposomes; Peptide Fragments; Phosphatidylethanolamines; Phospholipids; Polymers; Receptors, Opioid; Sensitivity and Specificity; Spectrometry, Fluorescence