Oxidation of aglycone of glycosphingolipids: serine and ceramide acid precursors for soluble glycoconjugates

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.

Kinetic analysis of binding between Shiga toxin and receptor glycolipid Gb3Cer by surface plasmon resonance

Shiga toxin (Stx) binds to the receptor glycolipid Gb3Cer on the cell surface and is responsible for hemolytic uremic syndrome. Stx has two isoforms, Stx1 and Stx2, and in clinical settings Stx2 is known to cause more severe symptoms, although the differences between the mechanisms of action of Stx1 and Stx2 are as yet unknown. In this study, the binding modes of these two isoforms to the receptor were investigated with a surface plasmon resonance analyzer to compare differences by real time receptor binding analysis. A sensor chip having a lipophilically modified dextran matrix or quasicrystalline hydrophobic layer was used to immobilize an amphipathic lipid layer that mimics the plasma membrane surface. Dose responsiveness was observed with both isoforms when either the toxin concentration or the Gb3Cer concentration was increased. In addition, this assay was shown to be specific, because neither Stx1 nor Stx2 bound to GM3, but both bound weakly to Gb4Cer. It was also shown that a number of fitting models can be used to analyze the sensorgrams obtained with different concentrations of the toxins, and the "bivalent analyte" model was found to best fit the interaction between Stxs and Gb3Cer. This shows that the interaction between Stxs and Gb3Cer in the lipid bilayer has a multivalent effect. The presence of cholesterol in the lipid bilayer significantly enhanced the binding of Stxs to Gb3Cer, although kinetics were unaffected. The association and dissociation rate constants of Stx1 were larger than those of Stx2: Stx2 binds to the receptor more slowly than Stx1 but, once bound, is difficult to dissociate. The data described herein clearly demonstrate differences between the binding properties of Stx1 and Stx2 and may facilitate understanding of the differences in clinical manifestations caused by these toxins.