Synthesis and characterization of new fluorescent glycolipid probes. Molecular organisation of glycosphingolipids in mixed-composition lipid bilayers

Abstract

The synthesis and properties of new fluorescent analogs of glycosphingolipids (galactosylcerebrosides, gangliosides G M1, G M3, G D1a and G D3 bearing a 9-anthrylvinyl or 3-perylenoyl residue in the acyl chain are described. The synthesis includes steps: (i) hydrolytic removal of the fatty acyl from the corresponding natural compound; (ii) reacylation of the sphingosine amino group with trans-12-(9-anthryl)-11-dodecenoic or 9-(3-perylenoyl)nonanoic acid; (iii) reacetylation of the neuraminic amino group (for gangliosides). Studies of the behavior of the fluorescent glycolipids in model membranes (multilayer liposomes and sonicated vesicles) revealed that the probes are largely lipid-specific, i.e. they behave in many aspects similar to their corresponding natural counterparts. Fluorescence anisotropy measurements and studies of fluorescence energy transfer from anthryvinyl- to perylenoyl-labeled probes suggest that in mixed bilayer systems containing approx. 10 mol% glycolipid, galactosylceramide is partly segregated from phospholipids even above the temperature of gel/liquid crystal transition of the phospholipid matrix. By contrast, no indication of lipid demixing was found for phospholipid/ganglioside systems containing up to 15 mol% glycolipid.