title: The role of sphingomyelin in regulating phase coexistence in complex lipid model membranes: competition between ceramide and cholesterol.
abstract: The structure, thermotropic phase behavior, dynamic motion and order parameters of bilayer dispersions of egg phosphatidylcholine, egg sphingomyelin, egg ceramide and cholesterol have been determined. The coexistence of gel, liquid-ordered and liquid-disordered structure has been determined by peak fitting analysis of synchrotron X-ray powder patterns. Order parameters and extent of distribution of 16-doxyl-stearic acid spin probe between ordered and disordered environments has been estimated by ESR spectral simulation methods. The presence of ceramide in proportions up to 20 mol% in phosphatidylcholine is characterized by gel-fluid phase coexistence at temperatures up to 46 degrees C depending on the amount of ceramide. Cholesterol tends to destabilize the ceramide-rich domains formed in phosphatidylcholine while sphingomyelin, by formation of stable complexes with ceramide, tends to stabilize these domains. The stability of sphingomyelin-ceramide complexes is evident from the persistence of highly ordered structure probed by ESR spectroscopy and appearance of a sharp wide-angle X-ray reflection at temperatures higher than the gel-fluid transition of ceramide alone in egg phosphatidylcholine bilayers. The competition between ceramide and cholesterol for interaction with sphingomyelin is discussed in terms of control of lipid-mediated signaling pathways by sphingomyelinase and phospholipase A2.
authors: Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.21, 1113 Sofia, Bulgaria. gstaneva@obzor.bio21.bas.bg
authors: Galya
authors: G
authors: Staneva
authors: Claude
authors: C
authors: Chachaty
authors: Claude
authors: C
authors: Wolf
authors: Kamen
authors: K
authors: Koumanov
authors: Peter J
authors: PJ
authors: Quinn
mesh_terms: D002518:Ceramides / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D004530:Egg Yolk / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005782:Gels; D008051:Lipid Bilayers / Q000737:chemistry*; D008567:Membranes, Artificial; D010713:Phosphatidylcholines / Q000737:chemistry; D013109:Sphingomyelins / Q000737:chemistry*; D013113:Spin Labels; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D002518:Ceramides; D005782:Gels; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D013113:Spin Labels; D002784:Cholesterol