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Stable and unstable lipid domains in ceramide-containing membranes.

ABSTRACT: We applied x-ray diffraction, calorimetry, and infrared spectroscopy to lipid mixtures of palmitoyl-oleoyl phosphatidylcholine, sphingomyelin, and ceramide. This combination of experimental techniques allowed us to probe the stability and structural properties of coexisting lipid domains without resorting to any molecular probes. In particular, we found unstable microscopic domains (compositional/phase fluctuations) in the absence of ceramide, and macroscopically separated fluid and gel phases upon addition of ceramide. We also observed phase fluctuations in the presence of ceramide within the broad phase transition regions. We compare our results with fluorescence spectroscopy data and complement the previously reported phase diagram. We also obtained electron paramagnetic resonance data to assess the possible limitations of techniques employing a single label. Our study demonstrates the necessity of applying a combination of experimental techniques to probe local/global structural and fast/slow motional properties in complex lipid mixtures.

SUBMITTER: Boulgaropoulos B

PROVIDER: S-EPMC3149230 | biostudies-other | 2011 May

REPOSITORIES: biostudies-other

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Stable and unstable lipid domains in ceramide-containing membranes.

Boulgaropoulos Beate B Arsov Zoran Z Laggner Peter P Pabst Georg G

Biophysical journal 20110501 9

We applied x-ray diffraction, calorimetry, and infrared spectroscopy to lipid mixtures of palmitoyl-oleoyl phosphatidylcholine, sphingomyelin, and ceramide. This combination of experimental techniques allowed us to probe the stability and structural properties of coexisting lipid domains without resorting to any molecular probes. In particular, we found unstable microscopic domains (compositional/phase fluctuations) in the absence of ceramide, and macroscopically separated fluid and gel phases u ...[more]

PMID: 21539783

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Project description:A uniquely sensitive method for ceramide domain detection allowed us to study in detail cholesterol-ceramide interactions in lipid bilayers with low (physiological) ceramide concentrations, ranging from low or no cholesterol (a situation similar to intracellular membranes, such as endoplasmic reticulum) to high cholesterol (similar to mammalian plasma membrane). Diverse fluorescence spectroscopy and microscopy experiments were conducted showing that for low cholesterol amounts ceramide segregates into gel domains that disappear upon increasing cholesterol levels. This was observed in different raft (sphingomyelin/cholesterol-containing) and non-raft (sphingomyelin-absent) membranes, i.e. mimicking different types of cell membranes. Cholesterol-ceramide interactions have been described mainly as raft sphingomyelin-dependent. Here sphingomyelin independence is demonstrated. In addition, ceramide-rich domains re-appear when either cholesterol is converted by cholesterol oxidase to cholestenone or the temperature is decreased. Ceramide is more soluble in cholesterol-rich fluid membranes than in cholesterol-poor ones, thereby increasing the chemical potential of cholesterol. Ceramide solubility depends on the average gel-fluid transition temperature of the remaining membrane lipids. The inability of cholestenone-rich membranes to dissolve ceramide gel domains shows that the cholesterol ordering and packing properties are fundamental to the mixing process. We also show that the solubility of cholesterol in ceramide domains is low. The results are rationalized by a ternary phospholipid/ceramide/cholesterol phase diagram, providing the framework for the better understanding of biochemical phenomena modulated by cholesterol-ceramide interactions such as cholesterol oxidase activity, lipoprotein metabolism, and lipid targeting in cancer therapy. It also suggests that the lipid compositions of different organelles are such that ceramide gel domains are not formed unless a stress or pathological situation occurs.

Dataset Information

Stable and unstable lipid domains in ceramide-containing membranes.

Publications

Stable and unstable lipid domains in ceramide-containing membranes.

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