title: Gel phase preference of ganglioside GM1 at low concentration in two-component, two-phase phosphatidylcholine bilayers depends upon the ceramide moiety.
abstract: In two-component phosphatidylcholine bilayers with coexisting liquid and P beta' gel phases, the distribution between phases of low concentrations of glycosphingolipids can be determined by freeze-etch electron microscopy after labeling the glycolipid with a suitable protein. We have found that the distribution depends upon the glycosphingolipid species (Rock, P. et al., (1991) Biochemistry 30, 19-25). Using this technique with cholera toxin as the protein label and bilayers formed from dipalmitoyl- and dielaidoylphosphatidylcholine (1:1) containing < 1 mol% GM1, we have studied the distribution of a family of GM1 homologues differing in the acyl chain and sphingoid base moieties. The GM1 preference for the P beta' ripple phase decreases with decreasing acyl chain length and increasing unsaturation. GM1 with either a C18:1 or C20:1 sphingoid base shows similar distributions in liquid and gel phases. When the molecules are preferentially found in the P beta' phase, they are positioned along unique loci in both A and A/2 forms of the ripple structure. This localization and acyl chain dependence reflect the volume, shape and localization of molecular packing defects in the P beta' phase. The ganglioside inclusions stabilize the P beta' phase and form compositional domains of unique topography.
authors.affiliation: Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Palestini
authors.forename: M
authors.initials: M
authors.lastname: Allietta
authors.forename: S
authors.initials: S
authors.lastname: Sonnino
authors.forename: G
authors.initials: G
authors.lastname: Tettamanti
authors.forename: T E
authors.initials: TE
authors.lastname: Thompson
authors.forename: T W
authors.initials: TW
authors.lastname: Tillack
mesh_terms: D000818:Animals; D002240:Carbohydrate Sequence; D002417:Cattle; D002518:Ceramides / Q000737:chemistry*; D002772:Cholera Toxin / Q000032:analysis; D005613:Freeze Etching; D005677:G(M1) Ganglioside / Q000737:chemistry*; D005782:Gels; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry*
chemical_list: D002518:Ceramides; D005782:Gels; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; D005677:G(M1) Ganglioside; D002772:Cholera Toxin