betadex and 1-2-linoleoylphosphatidylcholine

Lipid self-organization is believed to be essential for shaping the lateral structure of membranes, but it is becoming increasingly clear that also membrane proteins can be involved in the maintenance of membrane architecture. Cholesterol is thought to be important for the lateral organization of eukaryotic cell membranes and has also been implicated to take part in the sorting of cellular transmembrane proteins. Hence, a good starting point for studying the influence of lipid-protein interactions on membrane trafficking is to find out how transmembrane proteins influence the lateral sorting of cholesterol in phospholipid bilayers. By measuring equilibrium partitioning of the fluorescent cholesterol analog cholestatrienol between large unilamellar vesicles and methyl-β-cyclodextrin the effect of hydrophobic matching on the affinity of sterols for phospholipid bilayers was determined. Sterol partitioning was measured in 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers with and without WALP19, WALP23 or WALP27 peptides. The results showed that the affinity of the sterol for the bilayers was affected by hydrophobic matching. An increasing positive hydrophobic mismatch led to stronger sterol binding to the bilayers (except in extreme situations), and a large negative hydrophobic mismatch decreased the affinity of the sterol for the bilayer. In addition, peptide insertion into the phospholipid bilayers was observed to depend on hydrophobic matching. In conclusion, the results showed that hydrophobic matching can affect lipid-protein interactions in a way that may facilitate the formation of lateral domains in cell membranes. This could be of importance in membrane trafficking.

Topics: 1,2-Dipalmitoylphosphatidylcholine; beta-Cyclodextrins; Biophysics; Cholestenes; Dimyristoylphosphatidylcholine; Dose-Response Relationship, Drug; Hydrophobic and Hydrophilic Interactions; Kinetics; Lipid Bilayers; Lipids; Models, Chemical; Models, Statistical; Peptides; Phosphatidylcholines; Phospholipids; Sterols

Unilamellar liposomes composed of natural phospholipids provide a new promising class of protective agents for hypothermic storage, cryopreservation, or freeze-drying of red blood cells (RBCs). In this study, FTIR spectroscopy, MALDI-TOF MS, and colorimetric assays were used to investigate the effects of liposomes composed of a homologous series of linear saturated phosphatidylcholine phospholipids (18:0; 16:0; 14:0; 12:0) on RBC membranes. RBCs were incubated with liposomes at 37°C and both the liposomal and the RBC fraction were analyzed after incubation. FTIR studies showed that liposomes composed of short acyl chain length lipids cause an increase in RBC membrane conformational disorder at suprazero temperatures, whereas long acyl chain length lipids were found to have little effects. The increased lipid conformational disorder in the RBC membranes coincided with a decrease in the cholesterol-to-phospholipid ratio. The opposite effects were found in the liposomes after incubation with RBCs. MALDI-TOF MS analysis showed the presence of short acyl chain length lipids (14:0 and 12:0) in RBC membranes after incubation, which was not observed after incubation with liposomes containing long acyl chain length lipids (18:0 and 16:0). Liposomes alter RBC membrane properties by cholesterol depletion and lipid addition.

Topics: beta-Cyclodextrins; Biophysics; Cholesterol; Colorimetry; Dimyristoylphosphatidylcholine; Erythrocyte Membrane; Humans; Lipids; Liposomes; Phosphatidylcholines; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Spectrophotometry, Infrared; Spectroscopy, Fourier Transform Infrared; Temperature

Cholesterol is distributed unevenly between different cellular membrane compartments, and the cholesterol content increases from the inner bilayers toward the plasma membrane. It has been suggested that this cholesterol gradient is important in the sorting of transmembrane proteins. Cholesterol has also been to shown play an important role in lateral organization of eukaryotic cell membranes. In this study the aim was to determine how transmembrane proteins influence the lateral distribution of cholesterol in phospholipid bilayers. Insight into this can be obtained by studying how cholesterol interacts with bilayer membranes of different composition in the presence of designed peptides that mimic the transmembrane helices of proteins. For this purpose we developed an assay in which the partitioning of the fluorescent cholesterol analog CTL between LUVs and mbetaCD can be measured. Comparison of how cholesterol and CTL partitioning between mbetaCD and phospholipid bilayers with different composition suggests that CTL sensed changes in bilayer composition similarly as cholesterol. Therefore, the results obtained with CTL can be used to understand cholesterol distribution in lipid bilayers. The effect of WALP23 on CTL partitioning between DMPC bilayers and mbetaCD was measured. From the results it was clear that WALP23 increased both the order in the bilayers (as seen from CTL and DPH anisotropy) and the affinity of the sterol for the bilayer in a concentration dependent way. Although WALP23 also increased the order in DLPC and POPC bilayers the effects on CTL partitioning was much smaller with these lipids. This indicates that proteins have the largest effect on sterol interactions with phospholipids that have longer and saturated acyl chains. KALP23 did not significantly affect the acyl chain order in the phospholipid bilayers, and inclusion of KALP23 into DMPC bilayers slightly decreased CTL partitioning into the bilayer. This shows that transmembrane proteins can both decrease and increase the affinity of sterols for the lipid bilayers surrounding proteins. This is likely to affect the sterol distribution within the bilayer and thereby the lateral organization in biomembranes.

Topics: Anisotropy; beta-Cyclodextrins; Cholestenes; Dimyristoylphosphatidylcholine; Diphenylhexatriene; Lipid Bilayers; Peptides; Phosphatidylcholines; Phospholipids