Abstract
The biophysical properties of sphingolipids containing lignoceric (C24:0) or nervonic (C24:1) fatty acyl residues have been studied in multicomponent lipid bilayers containing cholesterol (Chol), by means of confocal microscopy, differential scanning calorimetry and atomic force microscopy. Lipid membranes composed of dioleoyl phosphatidylcholine and cholesterol were prepared, with the addition of different combinations of ceramides (C24:0 and/or C24:1) and sphingomyelins (C24:0 and/or C24:1). Results point to C24:0 sphingolipids, namely lignoceroyl sphingomyelin (lSM) and lignoceroyl ceramide (lCer), having higher membrane rigidifying properties than their C24:1 homologues (nervonoyl SM, nSM, or nervonoyl Cer, nCer), although with a similar strong capacity to induce segregated gel phases. In the case of the lSM-lCer multicomponent system, the segregated phases have a peculiar fibrillar or fern-like morphology. Moreover, the combination of C24:0 and C24:1 sphingolipids generates interesting events, such as a generalized bilayer dynamism/instability of supported planar bilayers. In some cases, these sphingolipids give rise to exothermic curves in thermograms. These peculiar features were not present in previous studies of C24:1 combined with C16:0 sphingolipids. Conclusions of our study point to nSM as a key factor governing the relative distribution of ceramides when both lCer and nCer are present. The data indicate that lCer could be easier to accommodate in multicomponent bilayers than its C16:0 counterpart. These results are relevant for events of membrane platform formation, in the context of sphingolipid-based signaling cascades.
Highlights
The biophysical properties of sphingolipids containing lignoceric (C24:0) or nervonic (C24:1) fatty acyl residues have been studied in multicomponent lipid bilayers containing cholesterol (Chol), by means of confocal microscopy, differential scanning calorimetry and atomic force microscopy
In terms of nanomechanical resistance, and of T m calculated by differential scanning calorimetry (DSC) experiments, the results were fairly consistent, as lignoceroyl sphingomyelin (lSM)-based samples exhibited transitions at higher T m and were more resistant to atomic force microscopy (AFM) probe indentation than those based on nSM
That study did not encounter some of the issues reported here, such as (i) the absence of domains in giant unilamellar vesicles (GUVs) (Fig. 2a) where Supported planar bilayer (SPB) did show them (Fig. 4a), (ii) the presence of exothermic signals in thermograms (Fig. 6e,h), or (iii) the observation of bilayer dynamism/instability (Fig. 5, S1, S2)
Summary
The biophysical properties of sphingolipids containing lignoceric (C24:0) or nervonic (C24:1) fatty acyl residues have been studied in multicomponent lipid bilayers containing cholesterol (Chol), by means of confocal microscopy, differential scanning calorimetry and atomic force microscopy. The importance of multicomponent membrane studies is increased when one of the lipids is cholesterol (Chol), because of the high prevalence of Chol in most animal membranes (25–50 mol% of total lipids depending on the cell line and subcellular organelle26,38,39) and due to the particular properties that Chol confers to the membrane Both Chol and Cer are highly hydrophobic molecules that tend to occupy the spaces between the lipid acyl chains, Cer give rise to highly packed and stoichiometrically constant gel phases in the Cer-enriched d omains[40], while Chol has a tendency to mix with phospholipids and induce ‘liquid-ordered’ ( Lo) phases, sometimes at the nano s cale. In planar bilayers containing both C24:0 and C24:1, dynamic (unstable) mixtures were observed where gel phases (domains) tended to disappear over time, at variance with our previous results obtained with C16:0 and C24:1 sphingolipids
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