Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update covering the period 2001-2002

A new naphthimidazole derivative for saccharide labeling with enhanced sensitivity in mass spectrometry detection

A series of saccharides, including maltoheptose, blood type B antigen, pullulan and the glucan of Ganoderma lucidum, are easily converted into the naphthimidazole (NAIM) derivatives in high yields by the iodine-promoted oxidative condensation. The NAIM-labeled saccharides, without further purification, show enhanced signals in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The combined use of NAIM derivatization and MALDI-TOFMS analysis thus provides a rapid method for identification of saccharides even in less than 1 pmol of saccharide in the sample. Characterization of the biologically active saccharides and complex polysaccharides is also achieved through the NAIM-derivatization method. This study can be further applied to facilitate the isolation and analysis of novel saccharides.

Imaging mass spectrometry of glycolipids

Mass spectrometry (MS) is an analytical technique that separates ionized molecules using differences in their mass, and can be used to determine the structure of the molecules. Matrix-assisted laser desorption/ionization (MALDI) is one of the most commonly used ionization methods for this procedure. A new technical method, imaging mass spectrometry (IMS), which is a two-dimensional MS, enables molecular imaging of tissue sections by the use of the MALDI-MS method. In this chapter, we briefly discuss available methods for analyzing glycolipids by IMS. We describe sample detection strategies, and also introduce a representative example of its research application.

Proton sponge: a novel and versatile MALDI matrix for the analysis of metabolites using mass spectrometry

Here, we show the usefulness of a strong base, 1,8-bis(dimethyl-amino)naphthalene (DMAN; proton sponge), as a novel matrix for MALDI-TOF/MS analysis of anions. Several strong and weakly acidic low-molecular-weight analytes (fatty acids, amino acids, fatty acid-amino acid conjugates, plant and animal hormones, vitamins, and short peptides) were measured at physiologically relevant concentrations. Clear negative-mode MALDI-TOF/MS spectra of all analytes using DMAN as the matrix show only deprotonated analyte signals at a low picomole/femtomole limit-of-detection. Moreover, the spectra were totally devoid of any matrix-related signals. Standard calibration curves gave good linearity over the entire picomole range: over two concentration orders in most cases and over three orders for peptides. Using this method, the crude regurgitate of the tobacco hornworm caterpillars (Manduca sexta, Lepidoptera, Sphingidae) was analyzed. As many as 11 different components were identified from a single spot, including 16:0, 18:2, 18:3, and 21:0 free acids and 5:0-Glu, 6:0-Glu, 18:2-Glu, 18:3-Glu, 16:0-Glu, and 16:3-Glu fatty acid-amino acid conjugates (FACs) in complete qualitative agreement with previously reported anion exchange-HPLC analyses. The identity of these components was confirmed by negative ion collision-induced dissociation (CID) MS2 spectra.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of oligosaccharides and oligosaccharide alditols obtained by hydrolysis of agaroses and carrageenans, two important types of red seaweed polysaccharides

MALDI-TOF mass spectrometry analyses of several oligosaccharides (aldoses) and oligosaccharide alditols derived from agaroses, kappa- and iota-carrageenans using different matrices (2,5-dihydroxybenzoic acid, nor-harmane, ferulic acid, and the ionic liquid matrices 2,5-dihydroxybenzoic acid-n-butylamine and ferulic acid-n-butylamine) were conducted. These carbohydrates were selected as model compounds to study the MALDI prompt and post-source decay (PSD) fragmentation processes of both families of oligosaccharides. Sulfated alditols showed in the negative-ion mode the molecular ion as [M-Na](-) together with the species yielded by their prompt fragmentation (mainly desulfation) while the sulfated oligosaccharides (aldoses) showed mainly glycosidic prompt fragmentation (glycosidic C-cleavages and desulfation). Non-sulfated aldoses and alditols, which could only be analyzed in positive-ion mode ([M+Na](+)), did not suffer any prompt fragmentation. The former yielded cross-ring fragmentation in the PSD mode. Best results were obtained by using 2,5-dihydroxybenzoic acid and/or nor-harmane as matrices for all the compounds studied.

Reverse thin layer method for enhanced ion yield of oligosaccharides in matrix-assisted laser desorption/ionization

A sample preparation method that is suitable for sensitive detection of underivatized oligosaccharides by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been investigated. As compared with the conventional dried-droplet or ethanol (EtOH) recrystallization method, superior mass spectra in terms of ion yield and signal-to-noise (s/n) ratio were obtained when methanol (MeOH) was used as a solvent for the mixture of matrix and oligosaccharides. Based on these results, a new sample preparation method, named the 'reverse thin layer method', was developed. This method comprises two steps: first, complete drying of the oligosaccharide solution on the MALDI target plate; and second, deposition of the matrix dissolved in a small amount of MeOH. Using this method, a relatively homogeneous matrix crystal was generated and higher yields of both positive and negative ions were obtained from oligosaccharides compared with conventional methods. Notably, the method can be applied to various matrices including both solid and liquid matrices.

Automated measurement of permethylated serum N-glycans by MALDI-linear ion trap mass spectrometry

The use of N-glycan mass spectrometry for clinical diagnostics requires the development of robust high-throughput profiling methods. Still, structural assignment of glycans requires additional information such as MS(2) fragmentation or exoglycosidase digestions. We present a setting which combines a MALDI ionization source with a linear ion trap analyzer. This instrumentation allows automated measurement of samples thanks to the crystal positioning system, combined with MS(n) sequencing options. 2,5-Dihydroxybenzoic acid, commonly used for the analysis of glycans, failed to produce the required reproducibility due to its non-homogeneous crystallization properties. In contrast, alpha-cyano-4-hydroxycinnamic acid provided a homogeneous crystallization pattern and reproducibility of the measurements. Using serum N-glycans as a test sample, we focused on the automation of data collection by optimizing the instrument settings. Glycan structures were confirmed by MS(2) analysis. Although sample processing still needs optimization, this method provides a reproducible and high-throughput approach for measurement of N-glycans using a MALDI-linear ion trap instrument.

Incoherent production reactions of positive and negative ions in matrix-assisted laser desorption/ionization

Utilizing synchronized dual-polarity matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, we found good evidence of the incoherent production of positive and negative matrix ions. Using thin, homogeneous 2,5-dehydroxybenzoic acid (DHB) matrix films, positive and negative matrix ions were found to appear at different threshold laser fluences. The presence of molecular matrix ions of single charge polarity suggests that the existence of DHB ion-pairs may not be a prerequisite in MALDI. Photoelectrons induced by the laser excitation may assist the production of negative DHB ions, as shown in experiments conducted with stainless steel and glass substrates. At high laser fluences, the relative yield of positive and negative matrix ions remained constant when homogeneous matrix films were used, but it fluctuated significantly with inhomogeneous crystal morphology. This result is also inconsistent with the hypothesis that matrix ion-pairs are essential primary ions. Evidence from both low and high laser fluences suggests that the productions of positive and negative matrix ions in MALDI may occur via independent pathways.

Application of flavonoids - quercetin and rutin - as new matrices for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of Pt(II) and Pd(II) complexes

Attempts are being made to overcome the resistance of tumour cells to platinum (Pt) drugs by the synthesis of new generations of Pt complexes, and it is important to find appropriate and simple methods for the characterization of those novel complexes. The additional applicability of such a method for the analysis of the interactions of metal complexes with biomolecules would be advantageous. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) seems to possess the capability to become this method of choice, since it could be applied to low-mass complexes as well as for the analysis of large biomolecules. In this work the applicability of flavonoids - quercetin and rutin - as matrices for MALDI-TOFMS analysis of dichlorido(ethylendiamine)platinum(II) ([PtCl(2)(en)]), dichlorido(diaminocyclohexane)platinum(II) ([PtCl(2)(dach)]) and chloride (diethylenetriamine) palladium(II) chloride ([PdCl(dien)]Cl) complexes is demonstrated. Spectra of Pt(II) and Pd(II) complexes recorded in the presence of quercetin and rutin are rather simple: Pt(II) complexes generate [M+Na](+) or [M+K](+)ions, whereas the investigated Pd(II) complex gives ions generated by the loss of one Cl(-) or HCl. Flavonoids give a relatively small number of well-defined ions in the low-mass region (at m/z 303.3 for quercetin and m/z 633.5 for rutin). Quercetin and rutin can be applied in much lower concentrations than other common MALDI matrices and require rather low laser intensity. We speculate that flavonoids stabilize the structures of the metal complexes and that they may be useful for the analysis of other biologically active metal complexes, thus implying their broader applicability.

Mass spectrometry in the characterization of human genetic N-glycosylation defects

Human genetic diseases that affect N-glycosylation result from the defective synthesis of the N-linked sugar moiety (glycan) of glycoproteins. The role of glycans for proper protein folding and biological functions is illustrated in the variety and severity of clinical manifestations shared by congenital disorders of glycosylation (CDG). This family of inherited metabolic disorders includes defects in the assembly of the oligosaccharide precursor that lead to an under-occupancy of N-glycosylation sites (CDG-I), and defects of glycan remodeling (CDG-II). Mass spectrometry constitutes a key tool for characterization of CDG-I defects by mass resolution of native protein glycoforms that differ for glycosylation-site occupancy. Glycan MS analyses in CDG-II is mandatory to detect whenever possible a repertoire of structures to pinpoint candidate enzymes and genes responsible for the abnormal N-glycan synthesis. In this manuscript, we review the MS applications in the area of CDG and related disorders with a special emphasis on those techniques that have been already applied or might become functional for diagnosis, characterization, and treatment monitoring in some specific conditions.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Application of pressure probe and UV-MALDI-TOF MS for direct analysis of plant underivatized carbohydrates in subpicoliter single-cell cytoplasm extract

Single-cell cytoplasm sap (1-10 pL) was extracted by using a pressure probe glass microcapillary tip from tulip leaf and bulb and analyzed by UV-MALDI-TOF MS for free underivatized carbohydrate content. Three matrices including 2,5-dihydroxybenzoic acid (DHB), 2,4,6-trihydroxyacetophenone (THAP), and carbon nanotubes (CNTs) in positive ion mode were selected for analysis because of acceptable carbohydrate-related signal reproducibility. Disaccharide and oligosaccharide (up to 15 Hex when THAP was used, 11 Hex with DHB, and 7 Hex with CNTs) were detected in tulip bulb cell cytoplasm sample. When DHB was used as matrix, neutral carbohydrates were more abundantly detected as sodiated cations; the sugar-related signals, however, appeared as dominant potassiated cations when THAP and CNTs were used. Small amount of monosaccharide was also detected in bulb cell cytoplasm with CNTs as matrix. UV-MALDI-TOF MS of leaf cell extract resulted in high-resolution detection of hexose and disaccharide with DHB, THAP, and CNTs.

Structure determination of beta-glucans from Ganoderma lucidum with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

A novel method that uses matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to analyze molecular weight and sequencing of glucan in Ganoderma lucidum is presented. Thus, β-glucan, which was isolated from fruiting bodies of G. lucidum, was measured in a direct and fast way using MALDI mass spectrometry. In addition, tandem mass spectrometry of permethylated glucans of G. lucidum, dextran, curdlan and maltohexaose were also pursued and different fragment patterns were obtained. The G. lucidum glucan structure was determined and this method for linkage analysis of permethylated glucan has been proven feasible.