Natural Ceramides and Lysophospholipids Cosegregate in Fluid Phosphatidylcholine Bilayers

Abstract

The mode of interactions between palmitoyl lysophosphatidylcholine (palmitoyl lyso-PC) or other lysophospholipids (lyso-PLs) and palmitoyl ceramide (PCer) or other ceramide analogs in dioleoylphosphatidylcholine (DOPC) bilayers has been examined. PCer is known to segregate laterally into a ceramide-rich phase at concentrations that depend on the nature of the ceramides and the co-phospholipids. In DOPC bilayers, PCer forms a ceramide-rich phase at concentrations above 10 mol%. In the presence of 20 mol% palmitoyl lyso-PC in the DOPC bilayer, the lateral segregation of PCer was markedly facilitated (segregation at lower PCer concentrations). The thermostability of the PCer-rich phase in the presence of palmitoyl lyso-PC was also increased compared to that in the absence of palmitoyl lyso-PC. Other saturated lyso-PLs (e.g., palmitoyl lyso-phosphatidylethanolamine and lyso-sphingomyelin) also facilitated the lateral segregation of PCer in a similar manner as palmitoyl lyso-PC. When examined in the DOPC bilayer, it appeared that the association between palmitoyl lyso-PC and PCer was equimolar in nature. It is proposed that the interaction of PCer with lyso-PLs was driven by the need of ceramide to obtain a large-headgroup co-lipid, and saturated lyso-PLs were preferred co-lipids over DOPC because of the nature of their acyl chain. Structural analogs of PCer (1-or 3-deoxy-PCer) were also associated with palmitoyl lyso-PC, similarly to PCer, suggesting that the ceramide/lyso-PL interaction was not sensitive to structural alterations in the ceramide molecule. Binary complexes containing palmitoyl lyso-PC and ceramide were prepared, and these had a bilayer structure as ascertained by transmission electron microscopy. It is concluded that ceramides and lyso-PLs associated with each other both in binary bilayers and in ternary systems based on the DOPC bilayers. This association may have biological relevance under conditions in which both sphingomyelinases and phospholipase A 2 enzymes are activated, such as during inflammatory processes.

Determination of the boundary lipids of sticholysins using tryptophan quenching

“…According to the manufacturer (Avanti Polar Lipids 57 ), this system is expected to yield samples with low polydispersity, if filters with pore size ≤ 200 nm are used. DLS measurements have confirmed this previously 58 and for the current samples (data not shown). Vesicle symmetry is expected to be maintained in the time between sample preparation and experiment.…”

Long acyl chain ceramides govern cholesterol and cytoskeleton dependence of membrane outer leaflet dynamics

“…Recently, it has been shown that in the membrane environment ceramides co-segregate with lysophospholipids due to their large headgroup 79 . The interaction with large headgroup lipids not certified by peer review) is the author/funder.…”