Complex Phase Behavior of GUVs Containing Different Sphingomyelins

Abstract

Understanding the lateral organization of biological membranes plays a key role on the road to fully appreciate the physiological functions of this fundamental barrier between the inside and outside regions of a cell. Ternary lipid bilayers composed of a high and a low melting temperature lipid and cholesterol represent a model system that mimics some of the important thermodynamical features of much more complex lipid mixtures such as those found in mammal membranes. The phase diagram of these ternary mixtures can be studied exploiting fluorescence microscopy in giant unilamellar vesicles, and it is typically expected to give rise, for specific combinations of composition and temperature, to regions of two-phase coexistence and a region with three-phase coexistence, namely, the liquid-ordered, liquid-disordered, and solid phases. Whereas the observation of two-phase coexistence is routinely possible using fluorescence microscopy, the three-phase region is more elusive to study. In this article, we show that particular lipid mixtures containing diphytanoyl-phosphatidylcholine and cholesterol plus different types of sphingomyelin (SM) are prone to produce bilayer regions with more than two levels of fluorescence intensity. We found that these intensity levels occur at low temperature and are linked to the copresence of long and asymmetric chains in SMs and diphytanoyl-phosphatidylcholine in the lipid mixtures. We discuss the possible interpretations for this observation in terms of bilayer phase organization in the presence of sphingolipids. Additionally, we also show that in some cases, liposomes in the three-phase coexistence state exhibit extreme sensitivity to lateral tension. We hypothesize that the appearance of the different phases is related to the asymmetric structure of SMs and to interdigitation effects.

Synthesis of Gb3 Glycosphingolipids with Labeled Head Groups: Distribution in Phase‐Separated Giant Unilamellar Vesicles

“…Exchanging asphingomyelin mixture with sphingomyelins with ad efined fatty acid is known to alter the phase separation behavior of ternary mixtures. [50] Five different SM species with as aturated fatty acid of varying length were chosen, namely palmitoyl SM (C 16:0 ), stearoyl SM (C 18:0 ), arachidoyl SM (C 20:0 ), behenoyl SM (C 22:0 ), and lignoceroyl SM (C 24:0 ), and the l o distribution of each Gb 3 species in these membranes was determined (Figure 6, Table 3).…”

Synthesis of Gb3 Glycosphingolipids with Labeled Head Groups: Distribution in Phase‐Separated Giant Unilamellar Vesicles

“…To investigate this aspect in more detail, we replaced the SM mixture isolated from pigs with synthetic pure SM. Exchanging a sphingomyelin mixture with sphingomyelins with a defined fatty acid is known to alter the phase separation behavior of ternary mixtures . Five different SM species with a saturated fatty acid of varying length were chosen, namely palmitoyl SM (C 16:0 ), stearoyl SM (C 18:0 ), arachidoyl SM (C 20:0 ), behenoyl SM (C 22:0 ), and lignoceroyl SM (C 24:0 ), and the l o distribution of each Gb 3 species in these membranes was determined (Figure , Table ).…”

Spectroscopic Analysis of the Binding of Paraquat and Diquat Herbicides to Biosubstrates

“…Recent studies showed the interest in testing the affinity to liposomes because these data may also complete information on bioaccumulation, which should not only be based on the hydrophobic nature of the compounds (partition octanol-water) [ 39 ]. Indeed, biophysical studies on the lipid model system which mimics some of the features of natural membranes and on membrane interactions by exogenous species provide important information on the possible mode of action of both healthy and toxic species [ 40 ]. For instance, antimicrobial peptides are found to strongly alter the characteristics of lipid bilayers: these interactions are crucial for the activity of the antibiotics and studies aimed at enlightening the details of these processes are crucial for developing improved pharmaceuticals [ 41 , 42 ].…”