Different effects of long- and short-chain ceramides on the gel-fluid and lamellar-hexagonal transitions of phospholipids: a calorimetric, NMR, and x-ray diffraction study.
The effects on dielaidoylphosphatidylethanolamine (DEPE) bilayers of ceramides containing different N-acyl chains have been studied by differential scanning calorimetry small angle x-ray diffraction and (31)P-NMR spectroscopy. N-palmitoyl (Cer16), N-hexanoyl (Cer6), and N-acetyl (Cer2) sphingosines have been used. Both the gel-fluid and the lamellar-inverted hexagonal transitions of DEPE have been examined in the presence of the various ceramides in the 0-25 mol % concentration range. Pure hydrated ceramides exhibit cooperative endothermic order-disorder transitions at 93 degrees C (Cer16), 60 degrees C (Cer6), and 54 degrees C (Cer2). In DEPE bilayers, Cer16 does not mix with the phospholipid in the gel phase, giving rise to high-melting ceramide-rich domains. Cer16 favors the lamellar-hexagonal transition of DEPE, decreasing the transition temperature. Cer2, on the other hand, is soluble in the gel phase of DEPE, decreasing the gel-fluid and increasing the lamellar-hexagonal transition temperatures, thus effectively stabilizing the lamellar fluid phase. In addition, Cer2 was peculiar in that no equilibrium could be reached for the Cer2-DEPE mixture above 60 degrees C, the lamellar-hexagonal transition shifting with time to temperatures beyond the instrumental range. The properties of Cer6 are intermediate between those of the other two, this ceramide decreasing both the gel-fluid and lamellar-hexagonal transition temperatures. Temperature-composition diagrams have been constructed for the mixtures of DEPE with each of the three ceramides. The different behavior of the long- and short-chain ceramides can be rationalized in terms of their different molecular geometries, Cer16 favoring negative curvature in the monolayers, thus inverted phases, and the opposite being true of the micelle-forming Cer2. These differences may be at the origin of the different physiological effects that are sometimes observed for the long- and short-chain ceramides.
Sot
Jesús
J
Unidad de Biofísica (Centro Mixto CSIC-UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, 48080 Bilbao, Spain.
Aranda
Francisco J
FJ
Collado
M-Isabel
MI
Goñi
Félix M
FM
Alonso
Alicia
A
D002151:Calorimetry; D002152:Calorimetry, Differential Scanning; D002518:Ceramides / Q000737:chemistry; D005782:Gels; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids / Q000737:chemistry; D008823:Micelles; D008968:Molecular Conformation; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
D002518:Ceramides; D005782:Gels; D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D008823:Micelles; D010714:Phosphatidylethanolamines; D010743:Phospholipids; C020888:1,2-dielaidoylphosphatidylethanolamine