Application of field desorption mass spectrometry for the analysis of sphingoglycolipids

Direct matrix-assisted laser desorption/ionization mass spectrometric analysis of glycosphingolipids on thin layer chromatographic plates and transfer membranes

Results are reported for analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) of native glycosphingolipids (GSLs) after development on thin layer chromatographic plates and after heat transfer of the GSLs from the plates to several types of polymer membranes. The spectral quality is better for membrane-bound analytes, in terms of sensitivity, mass resolution and background interference. The sensitivity gain compared with liquid secondary ion mass spectrometry (LSIMS) of GSLs on thin layer plates is 1-2 orders of magnitude (detection limits of 5-50 pmol vs. 1-10 nmol). Resolution and mass accuracy (0.1%) are limited by the irregular membrane surfaces and this effect cannot be entirely compensated by delayed extraction. The best results were obtained with a polyvinylidene difluoride (PVDF) P membrane, with irradiation from a nitrogen laser. Although the Nafion membrane could not be used for molecular weight profiling, its acidic character led to sample hydrolysis at the glycosidic linkages, thus yielding a series of fragments that could be used to determine the sequence of carbohydrate residues. Structural information could also be obtained by post-source decay (PSD) experiments on mass-selected precursor ions. Samples containing both neutral and acidic components were characterized in a 1:1 combination of 2, 5-dihydroxybenzoic acid and 2-amino-5-nitropyridine. GSLs that exhibited binding to antibodies in an overlay assay on the TLC plate were transferred to membranes and analyzed by MALDI-TOFMS without interference from the antibody or the salts and buffers used during the binding and visualization steps. Taking advantage of the insights into sample preparation gained from these studies, future research will extend this approach to analysis by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICRMS) with an external ion source.

High-energy collision-induced dissociation of ceramide ions from permethylated glycosphingolipids

Ceramide fragments from permethylated glycosphingolipids (GSLs) were studied by highenergy collision-induced dissociation (CID). In comparison with ceramlde fragments of underivatized GSLs, many more product ions including charge-remote fragment ions were observed. These ions provided detailed structural information on the ceramides. The relative intensity and the mass interval between the L and M ions were used to assign the position of the double bond. The position of the hydroxyl group was assigned with the Ln and K ions. Because the ceramide fragments and not the pseudomolecular ions were selected as the precursor ions, the size of GSLs had little effect on the quality of the product ion spectra. The sensitivity of this approach was in the range of picomoles.

Chromatographic and antigenic properties of Echinococcus granulosus hydatid cyst-derived glycolipids

The neutral and acidic fraction glycolipids of Echinococcus granulosus metacestode tissue compartments were isolated, defined by their chromatographic and antigenic properties, and assessed as to their efficacy as antigens in the serodiagnosis of human hepatic cystic and alveolar echinococcosis, and other helminthiases. Analyses were accomplished by thin-layer chromatography immunostaining and ELISA. The neutral glycolipid fraction's major carbohydrate epitope was the same as or very similar to that of Taenia crassiceps neutral glyco(sphingo)lipids, as represented by the 'neogala'-series core structure. The blood group-active, carbohydrate epitope P1 was expressed by a number of neutral fraction glycolipid component bands. The reverse-phase, thin-layer chromatography-isolated neutral fraction glycolipid component, designated Ag1, was efficient in the serological discrimination of cystic echinococcosis medium to high-titred sera. Ag1 did not specifically discriminate low-titred sera, i.e., other human helminthiases. The detected sialic acid residues of the acidic fraction glycolipids, on enzymatic cleavage, were identified as N-acylneuraminic acid and terminal. The acidic fraction glycolipids exhibited the paradox of only chemically minor components being antigenic towards cystic and alveolar echinococcosis infection sera. The combined acidic fraction glycolipid components Ra and Rx were capable of serological discrimination between cystic echinococcosis, alveolar echinococcosis and other helminthiases.

Analysis of underivatized glycosphingolipids by high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry

Analytical conditions for underivatized glycosphingolipids by using high-performance liquid chromatography atmospheric pressure ionization mass spectrometry (HPLC/API-MS) were investigated. The analysis was performed by using an ordinary reversed-phase column (4.6 X 150 or 4.6 X 250 mm) at a flow rate of 1 ml/min. The glycosphingolipids could be characterized from the HPLC/API-MS in terms of molecular weight, ceramide composition, and partial oligosaccharide sequence. In order to obtain an adequate spectrum the amount of material needed is in the range of a few micrograms of lipid. By selected ion monitoring the sensitivity of the method allowed characterization of only 60 ng of glycosphingolipid. The method will be very useful in the characterization of small quantities of glycosphingolipids from biological samples.

Direct analysis of glycolipids on thin-layer plates by matrix-assisted secondary ion mass spectrometry: application for glycolipid storage disorders

The lipids accumulated in organs of patients with Gaucher's, Tay-Sachs, and Fabry's disease were identified by means of the combination of thin-layer chromatography and matrix-assisted secondary ion mass spectrometry. The total lipid extract of each lipidosis tissue was chromatographed on a TLC plate and then analyzed directly by mass spectrometry without elution of the sample from the TLC plate. The amount of material needed to obtain an adequate spectrum is in the order of a few micrograms of lipids per band for both positive and negative ion detection. By scanning the plates, mass spectral and chromatographic information can be obtained simultaneously, which was shown to be useful for the qualitative identification of the components on the plates.

Application of field desorption and secondary ion mass spectrometry for glycolipid analysis

Field desorption (FD) and secondary ion mass spectrometry (SI-MS) mass spectra of several glycolipids are presented to demonstrate their potential for the analysis of glycolipids. FD and SI-MS give useful information on molecular weight, ceramide structure and sugar sequence. In general, FD provides clearer fragment ion peaks for the analysis of sugar sequence than SI-MS. For underivatized acidic glycolipids such as gangliosides, sulfatide and seminolipid, SI-MS provides quasimolecular ions which are hardly produced by FD. In contrast to underivatized gangliosides, permethylated samples give molecular ion species of high intensity in both FD and SI-MS, but no fragment ions pertinent to carbohydrate sequence could be observed in FD spectra. SI-MS spectra of permethylated samples provide good information on sugar chain structure. Thus FD and SI-MS mass spectra complement each other, and the combination of these ionization methods will provide powerful tools for glycolipid analysis.

A novel neutral oligosaccharide chain found in polysialoglycoproteins isolated from Pacific salmon eggs. Structural studies by secondary ion mass spectrometry, proton nuclear magnetic resonance spectroscopy, and chemical methods

A novel carbohydrate chain possessing a hitherto unknown disaccharide unit, alpha-L-Fuc leads to D-GalNAc, has been isolated from salmon egg polysialoglycoproteins on alkali-borohydride treatment. Salmon egg polysialoglycoproteins contain O-glycosidically linked neutral pentasaccharide chains in addition to a number of oligosialosyl group containing sugar chains. Composition analysis of the neutral pentasaccharide gave fucose, galactose, 2-acetamido-2-deoxygalactose, and 2-acetamido-2-deoxygalactitol in a molar ratio of 1:2:1:1. The structure was determined to be alpha-L-Fuc(1 leads to 3)-beta-D-GalNAc-(1 leads to 3)-beta-D-Gal(1 leads to 4)-beta-D-Gal(1 leads to 3)-D-GalNAcol by the following three major procedures: First, the sequential order of the constitutional monosaccharides was determined by secondary ion mass spectrometry before and after permethylation. Second, linkages were established by methylation analysis and Smith degradation and hydrazinolysis-nitrous deamination studies. Third, anomeric configuration of the glycosidic linkages involved was deduced from 270-MHz proton nuclear magnetic resonance spectroscopy.