Radioisotopic assay for galactocerebrosides and sulfatides

Heat-stabilized glycosphingolipid films for biosensing applications

We have investigated a means of producing thin, oriented lipid monolayers which are stable under repeated washing and which may be useful in biosensing or surface-coating applications. Phosphatidylcholine and the glycosphingolipid GM1 were used as representative lipids for this work. Initially, a mixed self-assembled monolayer of octanethiol and hexadecanethiol was produced on a gold surface. This hydrophobic monolayer was then brought into contact with a thin lipid film that had been assembled at the liquid/air interface of a solution, allowing the lipid to deposit on the gold surface through hydrophobic interactions. The lipid layer was then heated to cause intermingling of the fatty acid and alkanethiol chains and cooled to form a highly stable film which withstood repeated rinsing and solution exposure. Presence and stability of the film were confirmed via ellipsometry, Fourier transform infrared spectroscopy, and quartz crystal microbalance (QCM), with an average overall film thickness of approximately 3.5 nm. This method was then utilized to produce GM1 layers on gold-coated QCM crystals for affinity sensing trials with cholera toxin. For these sensing elements, the lower detection limit of cholera toxin was found to be approximately 0.5 microg/mL, with a logarithmic relationship between toxin concentration and frequency response spanning over several orders of magnitude. Potential sites for nonspecific adsorption were blocked using serum albumin without sacrificing toxin specificity.

Direct Analysis of Silica Gel Extracts from Immunostained Glycosphingolipids by Nanoelectrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry

A combined strategy of preparative high-performance thin-layer chromatography overlay assay and mass spectrometry was established for the structural characterization of immunostained glycosphingolipids (GSLs) in silica gel extracts. Crude chloroform/methanol/water (30/60/8, v/v/v) extracts of immunostained TLC bands were analyzed by nanoelectrospray low-energy CID mass spectrometry without further purification. The GSL species investigated were isomeric monosialogangliosides of the neolacto series from a ganglioside preparation of human granulocytes, the disialoganglioside GD3 from a human melanoma lipid extract, and ganglio series Gg3Cer of a neutral GSL preparation from murine lymphoreticular MDAY-D2 cells. For the specific detection of lipid-bound oligosaccharides, polyclonal chicken IgY, murine monoclonal IgG3, and IgM antibodies were used. The resulting mass spectra show that only analytical quantities of approximately 1 microg of a single GSL within a complex mixture are required for the structure determination of immunostained GSLs by MS and MS/MS. All species investigated were detected as singly charged deprotonated molecular ions, and neither buffer-derived salt adducts nor coextracted contaminants from the immunostaining procedure or the silica gel layer were observed. This effective HPTLC-MS-joined procedure offers a wide range of applications for any carbohydrate binding agents such as bacterial toxins, plant lectins, and others.

Oxidation of glycolipids in liposomes by galactose oxidase

Small unilamellar phosphatidylcholine vesicles containing globo-series glycolipids were labeled by the galactose oxidase/NaB[3H]4 procedure. The major glycolipid of human red cells, globoside, was the best substrate for galactose oxidase both in vesicles and in tetrahydrofuran-containing buffer. The oxidation rates of membrane-bound ceramide trihexoside and Forssman glycolipid were one-fourth and one-tenth, respectively, of the oxidation rate of globoside. Membrane-bound ceramide dihexoside was not a substrate for galactose oxidase, although it was readily oxidized in tetrahydrofuran-containing buffer. Soluble sialoglycoproteins and membrane-incorporated glycophorin A stimulated the oxidation of globoside-containing vesicles, whereas membrane-bound GD1a ganglioside had no effect on globoside oxidation.

A monoclonal antibody with reactivity to asialo GM1 and murine natural killer cells

A monoclonal antibody (MAb) was prepared by the fusion of murine SP2-O myeloma cells with BALB/cByJ spleen cells that were immunized with the glycolipid asialo GM1 adsorbed to naked Salmonella. The specificity of the IgM antibody obtained was defined using various glycolipids, cell extracts and saccharides in ELISA assays and thin-layer chromatography (TLC) immunoblots. The non-reducing terminal galactose is the immunodominant residue for this antibody; however, there is undetectable reactivity to free galactose, galactosylceramide or compounds with an alpha-linked galactose. The SH-34 antibody specifically lyses asialo GM1-expressing macrophages in the presence of complement and removes NK cells in vitro from spleen cell populations. When the specificity of the MAb was compared to that of a commercially available rabbit antiserum to asialo GM1, it was found that both cross-reacted with GM1 and asialo GM3 at high antibody concns; however, the MAb did not bind asialo GM2 while the rabbit antiserum showed substantial reactivity to this glycolipid. It is anticipated that this MAb will be useful for the study of murine and rat natural killer cells.