The role of PS 18:0/18:1 in membrane function

Abstract

Various studies have demonstrated that the two leaflets of cellular membranes interact, potentially through so-called interdigitation between the fatty acyl groups. While the molecular mechanism underlying interleaflet coupling remains to be fully understood, recent results suggest interactions between the very-long-chain sphingolipids in the outer leaflet, and phosphatidylserine PS18:0/18:1 in the inner leaflet, and an important role for cholesterol for these interactions. Here we review the evidence that cross-linking of sphingolipids may result in clustering of phosphatidylserine and transfer of signals to the cytosol. Although much remains to be uncovered, the molecular properties and abundance of PS 18:0/18:1 suggest a unique role for this lipid.

The role of lipid species in membranes and cancer-related changes

“…Interesting in this connection is the remarkably similar enrichment of CHOL, SM, and PS from CHO cells to detergent-resistant membranes (DRMs) as well as rafts isolated without detergent [21] as the enrichments observed for these lipid classes in exosomes excreted from PC-3 cells [20]. In a recent review, we discussed the role of PS18:0/18:1 in membrane function and showed that data published from several laboratories indicate that this lipid species has an important function in coupling the two leaflets due to interactions with sphingolipids and CHOL [10].…”

“…The different conclusions drawn from such studies strongly suggest that some of the methods used cannot be trusted, and we refer to an excellent review article where this controversial issue is summarized [15]. Based on the very high content of CHOL in some membranes, we find it difficult to understand how CHOL can be located mainly in one of the two leaflets, as we recently have discussed [10].…”

“…Lipid rafts have for many years been stated to be enriched in saturated phospholipids, and most models of lipid rafts contain phospholipids with two saturated fatty acyl chains. We recently challenged this view [10] since the phospholipid composition published for lipid rafts [21,29], the apical raftlike membrane of MDCK cells [14] and different cell lines contain very little of lipids with two saturated fatty acyl chains [10]. In an early and very detailed study of the lipid composition of DRMs it was stated that "a phospholipid was deemed saturated if containing no more than one double bond" [21].…”

“…It should be noted that it is now possible to make asymmetric liposomes [45]. We have recently discussed the importance of using both asymmetric models and lipid species commonly present in cell membranes to mimic such membranes in an optimal way in future studies with liposomes or in simulation studies [10].…”

“…Glycosphingolipids normally contain very little of Namidated fatty acyl chains with 18 or 20 carbon atoms, and they also contain very little of unsaturated fatty acyl chains, except for C24:1 species which may contribute even more than 50% of the total species of the class [9]. The reason for this bimodal distribution of glycosphingolipid species is not known, but it should be noted that the species containing Namidated C16:0 will reach approximately to the middle of the b i l a y e r s ( s i m i l a r t o t h a t o b t a i n e d b y m o s t glycerophospholipids), whereas the sphingolipids containing 24 carbon atoms could reach approximately halfway into the other leaflet, thus giving a flexibility for different strength of interactions between the sphingolipids in one leaflet and the lipids in the other leaflet [10].…”