F.A.B.-mass spectrometry of carbohydrates

Structural studies of the O-antigenic polysaccharide of Fusobacterium necrophorum

The O-specific polysaccharide component of the lipopolysaccharide produced by Fusobacterium necrophorum is of the teichoic acid type, with repeating units connected by phosphoric diester linkages. Dephosphorylation of the polysaccharide by treatment with aqueous hydrogen fluoride yielded a carbohydrate composed of a trisaccharide linked to an acidic component. This product, and the polysaccharide, were investigated by chemical methods and 1H-, 13C-, 31P- and 15N-NMR spectroscopy and the former also by fast-atom-bombardment mass spectrometry. It is proposed that the polysaccharide is composed of repeating units having the following structure, in which Fuc represents fucose (6-deoxy-galactose), Am represents an acetamidino group and Sug 2,4-diamino-2,4,6-trideoxy-D-glucose ('bacillosamine') acetylated at the 2-position and acylated with a (S)-3-hydroxybutanoic acid at the 4-position. The acid was identified as a 2-amino-2-deoxy-2-C-methyl-pentonic acid (2-amino-2-methyl-3,4,5-trihydroxypentanoic acid). The configuration of this acid remains to be determined. [formula: see text]

Collision-induced dissociation of alkali metal cationized and permethylated oligosaccharides: Influence of the collision energy and of the collision gas for the assignment of linkage position

Tandem mass spectrometry has been used to study the collision-induced decomposition of [M+Na](+) ions of permethylated oligosaccharides. It is shown that many linkage positions in one compound may be determined by the presence or absence, in a single spectrum, of specific fragment ions that arise from the cleavage of two ring bonds and that the yield of such ions depends strongly on the collision energy and nature of the collision gas. In contrast to the behavior of monolithiated native oligosaccharides, the collision-induced decomposition of the sodiated and permethylated oligosaccharide samples at low energy leads to preferential cleavage of glycosidic linkages. At high collision energies, the fragment ions formed by cleavage of more than one bond are greatly enhanced, especially when helium is replaced by argon as the collision gas. Furthermore, argon is the more efficient collision gas in inducing fragmentation of the precursor ions. As an example of the application of this method, the discrimination between the 1 → 3 and 1 → 6-linked mannose residues in the common core of N-glycans is described.

"Slow" metastable decomposition of oligosaccharide cations produced in an external source fourier transform mass spectrometer

Unimolecular metastable decomposition of cucyclodextrin cations is observed in a fast-atom bombardment Fourier transform mass spectrometry instrument. Cleavage reactions occur at the glycosidic bonds to produce oligomeric fragment ions. The first-order rate constant for the decay of the protonated parent was measured and found to be (4.2 ± 1.0) × 10(2)s(-1).

The structure of an antigenic glycolipid (SL-IV) from Mycobacterium tuberculosis

The structure of an antigenic glycolipid isolated recently from cell walls of various strains of Mycobacterium tuberculosis and believed to be a sulfolipid consisting chiefly of 2,3-di-O-(hexadecanoyl/octadecanoyl)-alpha,alpha-trehalose 2'-sulfate (designated as SL-IV), was reinvestigated by mass spectrometry and nuclear magnetic resonance spectroscopy. The material proved to be a complex mixture of closely related components which are indeed 2,3-di-O-acyltrehaloses. However, no sulfate group was found in the antigen, and revision of its designation as a sulfolipid is therefore required. The lipid substituents comprise an estimated 20% of C14-C19 fatty acids, including tetradecanoic (myristic), 9-tetradecenoic (myristoleic), 9-hexadecenoic (palmitoleic), 9-octadecenoic (oleic), 10-methylhexadecanoic (tuberculopalmitic), and 10-methyloctadecanoic (tuberculostearic) acids in addition to hexadecanoic (palmitic) and octadecanoic (stearic) acids, and approximately 80% of higher, methyl-branched acids. Among the latter are, principally, 2,4-dimethyldocosanoic and 3-hydroxy-2,4,6- trimethyltetracosanoic acids, and a smaller proportion of 2,4,6-trimethyltetracos-2-enoic acid. Numerous further acids, related to those mentioned by methylene homology, are also present in small proportions.

Selective identification and differentiation of N- and O-linked oligosaccharides in glycoproteins by liquid chromatography-mass spectrometry

A mass spectrometry method has been developed for selective detection of glycopeptides at the low (< or = 25) picomole level during chromatography of glycoprotein digests and for differentiation of O-linked from N-linked oligosaccharides. The technique involves observation of diagnostic sugar oxonium-ion fragments, particularly the HexNAc+ fragment at m/z 204, from collisionally excited glycopeptides. Collision-induced fragmentation can be accomplished in either of two regions of a triple quadrupole mass spectrometer equipped with an atmospheric pressure, electrospray (ES) ionization source. If collisions before the first quadrupole are chosen, it is possible to enhance formation of carbohydrate-related fragment ions without distorting the distribution of peptide and glycopeptide signals by increasing the collisional excitation potential only during that portion of each scan in which the low mass carbohydrate-related ions are being detected. This procedure, requiring only a single quadrupole instrument, identifies putative glycopeptide-containing fractions in the chromatogram but suffers from a lack of specificity in the case of co-eluting peptides. Increased specificity is obtained by selectively detecting only those parent ions that fragment in Q2, the second collision region of the triple quadrupole, to produce an ion at m/z 204 (HexNAc+). Only (M + H)+ ions of glycopeptides are observed in these liquid chromatography-electrospray tandem mass spectrometry (LC-ESMS/MS) "parent-scan" spectra. N-linked carbohydrates are differentiated from O-linked by LC-ESMS/MS analysis of the digested glycoprotein prior to and after selective removal of N-linked carbohydrates by peptide N:glycosidase F. These methods, which constitute the first liquid chromatography-mass spectrometry (LC-MS)-based strategies for selective identification of glycopeptides in complex mixtures, facilitate location and preparative fractionation of glycopeptides for further structural characterization. In addition, these techniques may be used to assess the compositional heterogeneity at specific attachment sites, and to define the sequence context of the attachment site in proteins of known sequence. The strategy is demonstrated for bovine fetuin, a 42-kDa glycoprotein containing three N-linked, and at least three O-linked carbohydrates. Over 90% of the fetuin protein sequence was also corroborated by these LC-ESMS studies.

Structure of the asn-linked oligosaccharides of apolipophorin III from the insect Locusta migratoria. Carbohydrate-linked 2-aminoethylphosphonate as a constituent of a glycoprotein

The primary structures of the N-linked carbohydrate chains of apolipophorin III from the insect Locusta migratoria have been determined. The glycoprotein was completely deglycosylated with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Released oligosaccharides were separated from the remaining protein using gel-permeation chromatography on Bio-Gel P-100. Purification of the carbohydrate chains was achieved by a combination of FPLC anion-exchange chromatography on Mono-Q and amine adsorption HPLC on Lichrosorb-NH2. The structures of the carbohydrate chains were deduced with a combination of fast atom bombardment mass spectrometry, 1H- and 31P-NMR spectroscopy, and methylation analysis. The majority of the carbohydrate chains contains 2-aminoethylphosphonate (AEP), which is linked to the 6-position of Man and/or GlcNAc. L. migratoria apolipophorin III is the first example of a glycoprotein containing carbohydrate-linked 2-aminoethylphosphonate. The structures of the major oligosaccharides were established to be the following: [formula: see text]

The gum exudate of Encephalartos longifolius Lehm. (female): further hydrolytic studies

Sequential, acid hydrolysis of the gum exudate from Encephalartos longifolius cones gave the neutral disaccharides beta-Gal-(1-->3)-Ara (1), beta-Gal-(1-->3)-Gal, and beta-Gal-(1-->6)-Gal; the triouronic acid beta-GlcA-(1-->6)-beta-Gal-(1-->3)-Ara (2); and the biouronic acids described earlier, namely, beta-GlcA-(1-->6)-Gal (3), beta-4-O-MeGlcA-(1-->6)-Gal, and beta-GlcA-(1-->2)-Man (4). Oligomers up to the tetramer of beta-GlcA-(1-->2)-Man alpha-linked through O-4 of GlcA characterised the inner, core region of the complex acidic polysaccharide. Alternating GlcA and Man residues were indicated by FABMS of methylated, acid-degraded gum. The presence of the constituent sugar units was confirmed by methylation of the gum and partition chromatography of the products of acid hydrolysis. Partial hydrolysis gave fractions containing terminal and in-chain GlcA attached to Gal and Man. Base-catalysed degradation of the methylated products showed Rha to be exterior to GlcA in the periphery.

Structure of the O-antigen of Escherichia coli 0119 lipopolysaccharide

The structure of the O-polysaccharide component of the lipopolysaccharide produced by Escherichia coli 0119 was determined by the use of methylation analysis, periodate oxidation, 1D and 2D nuclear magnetic resonance spectroscopy, and mass spectrometric methods. The O-polysaccharide was found to be a high molecular weight polymer of a repeating pentasaccharide unit composed of D-mannose, D-galactose, L-rhamnose, 2-acetamido-2-deoxy-D-glucose, and 2-acetamido-2,3-dideoxy-3-formamido-D-rhamnose residues (1:1:1:1:1) and had the structure: [formula: see text]

Human urokinase contains GalNAc beta (1-4)[Fuc alpha (1-3)]GlcNAc beta (1-2) as a novel terminal element in N-linked carbohydrate chains

Structural analysis of enzymically released N-linked carbohydrate chains of human urokinase (urinary-type plasminogen activator) by 1H NMR spectroscopy and FAB-MS demonstrated that the N-linked oligosaccharides on the only N-glycosylation site contain diantennary structures with the novel GalNAc beta (1-4) [Fuc alpha (1-3)]GlcNAc beta (1-2) element in the upper or the lower branch.

Incompletely processed N-glycans of serum glycoproteins in congenital dyserythropoietic anaemia type II (HEMPAS)

Congenital dyserythropoietic anaemia type II, or HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum lysis test) is a genetic disease caused by membrane disorganization of erythroid cells. The primary defect of this disease lies in the gene encoding enzyme(s) which is responsible for the biosynthesis of Asn-linked oligosaccharides chains of glycoproteins (Fukuda et al, 1990). In order to know whether this gene defect affects the glycosylation in the cells other than the erythroid cells, the carbohydrate structures of the transferrin isolated from the sera of HEMPAS patients were analysed. Fast atom bombardment mass spectrometry analysis showed the presence of high mannose type and hybrid type oligosaccharides in the HEMPAS transferrin which is in contrast to the complex-type oligosaccharides found in the normal transferrin. The results strongly suggest that biosynthesis of Asn-linked oligosaccharide chains in HEMPAS hepatocytes is disturbed. As a result, the serum glycoproteins with incompletely processed carbohydrates are circulating in the plasma in HEMPAS patients, but they must have been absorbed by the cells in the liver and the reticuloendothelial cells. Upon intravenous infusion into rats, as much as 30% of the HEMPAS transferrin was cleared from the plasma circulation. The majority of the HEMPAS transferrins was taken up by the liver, and transferrin was distributed both in the hepatocytes and the Kupffer cells. The presence of enormous amounts of aberrantly glycosylated serum glycoproteins may lead to the liver cirrhosis and secondary tissue siderosis seen in HEMPAS patients.

Characterization of lipid A from Pseudomonas aeruginosa O-antigenic B band lipopolysaccharide by 1D and 2D NMR and mass spectral analysis

The Lipid A from the lipopolysaccharide of Pseudomonas aeruginosa was examined by high-field nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). The backbone structure and the position of phosphate substituents were unambiguously established by one- and two-dimensional 1H, 13C, and 31P NMR techniques on a de-O-acylated Lipid A sample. The Lipid A has a beta-(1,6)-glucosamine disaccharide structure which is substituted by phosphomonoesters through glycosidic bonds at C-1 and at C-4'. The configuration of the glycosidically linked phosphate at position C-1 was identified as alpha which is the same as that of Enterobacterial Lipid A. Chemical analysis revealed that the Lipid A contained 2-hydroxydodecanoic, 3-hydroxydodecanoic, dodecanoic, 3-hydroxydecanoic, and hexadecanoic acids in the approximate molar ratios 2.2:2.0:0.2:0.8:0.4. From 1H NMR and fast atom bombardment (FAB) mass spectrometry on the de-O-acylated Lipid A, it was established that both glucosamine residues were N-acylated by 3-hydroxydodecanoic acid. The identity and positions of the ester bound fatty acids in the intact Lipid A were investigated by negative ion FAB-MS. In addition to the hexaacyl and pentaacyl Lipid A species, a tetraacyl species was identified. Heterogeneity due to hydroxylated and nonhydroxylated dodecanoic acid esters could be uniquely localized to the nonreducing beta-glucosamine residue from the fragmentation pattern observed in the negative ion FAB-MS. The complete structure of the Lipid A from P. aeruginosa will be useful in understanding the determinants responsible for the endotoxin activity of this molecule.

The determination of glycopeptides by liquid chromatography/mass spectrometry with collision-induced dissociation

Glycopeptides derived from ribonuclease B and ovomucoid have been subjected to collisioninduced dissociation (CID) in the second quadrupole of a triple quadrupole mass spectrometer. Doubly charged parent ions gave predictable fragmentation that yielded partial sequence information of the attached oligosaccharide as Hex and HexNAc units. Common oxonium ions are observed in the product ion mass spectra of the glycopeptides that correspond to HexNAc(+) (m/z 204) and HexHexNAc(+) (m/z 366). A strategy for locating the glycopeptides in the proteolytic digest mixtures of glycoproteins by ions spray liquid chromatography mass spectrometry (LC/MS) is described by utilizing CID in the declustering region of the atmospheric pressure ionization mass spectrometer to produce these characteristic oxonium ions. This LC/CID/MS approach is used to identify glycopeptides in proteolytic digest mixtures of ovomucoid, asialofetuin, and fetuin. LC/CID/MS in the selected ion monitoring mode may be used to identify putative glycopeptides from the proteolytic digest of fetuin.

Molecular structures of glycoprotein hormones and functions of their carbohydrate components

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NMR spectroscopy in the structural elucidation of oligosaccharides and glycosides

The potential of one- and two-dimensional NMR techniques for the identification of individual sugar residues, their anomeric configuration, interglycosidic linkages, sequencing and the site of any appended group, in establishing the structures of naturally occurring oligosaccharides and glycosides is presented.

Fast sequencing of oligosaccharides: the reagent-array analysis method

A method of oligosaccharide analysis involving controlled fragmentation resulting from enzymatic digestion is presented. The principle involves generating a set of fragments from the original oligosaccharides, characterizing them in terms of their hydrodynamic volumes, determining their molar proportions, and identifying the oligosaccharides by comparison with a computer-generated data base. Experimentally, this technique involves incubation of aliquots of a sample with a set of defined mixtures of exoglycosidases followed by pooling of the products and a single analysis on the product pool. This method has several practical advantages over current techniques, including speed and the ability to use smaller amounts of starting material. The detection of the intensity-versus-hydrodynamic volume profile is limited only by the specific activity of the labeling method. The ability to perform the enzyme digestions is limited by the individual Km values of the enzymes.

Structures of the O chains from lipopolysaccharides of Campylobacter jejuni serotypes O:23 and O:36

Lipopolysaccharides of C. jejuni serotypes O:23 and O:36 have been shown to contain structurally variable O polysaccharide chains with repeating units of four closely-related types: ----3)-beta-D-GlcpNAc-(1----3)-alpha-D-Galp-(1----2)-6d-alpha-D-alt-H epp-(1---- , ----3)-beta-D-GlcpNAc-(1----3)-alpha-D-Galp-(1----2)-6d-3-Me-alpha-D-alt -Hepp- (1----, ----3)-beta-D-GlcpNAc-(1----3)-alpha-D-Galp-(1----2)-D-glycero-alpha-D-a lt-Hepp - (1----, and ----3)-beta-D-GlcpNAc-(1----3)-alpha-D-Galp-(1----2)-3-Me-D-glycero-alph a-D-alt - Hepp-(1----. Structural methods included 1H- and 13C-NMR spectroscopy, methylation linkage analysis, fast atom bombardment mass spectrometry of methylated glycans, and selective fragmentations by the Smith degradation and N-deacetylation-nitrous acid deamination.

Effect of enzymatic deglycosylation on the regenerability of bovine rhodopsin

The influence of the carbohydrate groups of rhodopsin on its ability to regenerate upon incubation with 11-cis retinaldehyde after photobleaching was examined. Rhodopsin was deglycosylated enzymatically with peptide-N-glycosidase F (PNGase F). Verification of deglycosylation was established by: (a) SDS-PAGE; (b) carbohydrate compositional analysis using high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD); (c) isolation and carbohydrate analysis by HPAEC-PAD and fast atom bombardment-mass spectrometry of the oligosaccharides liberated from rhodopsin; and (d) absence of reactivity with lectins. Deglycosylated rhodopsin, when present either in rod outer segments or after purification, exhibited the same absorption spectrum as the native molecule. After photobleaching, deglycosylated rhodopsin reacted with 11-cis retinaldehyde in a manner similar to the native material, restoring the spectral properties lost after light-exposure. The carbohydrate portion, therefore, was not required for expressing the spectral properties of rhodopsin nor for regeneration of the photobleached visual pigment.

Liquid secondary ion mass spectrometry analysis of permethylated, n-hexylamine derivatized oligosaccharides. Application to baculovirus expressed mouse interleukin-3

Reductive amination with n-hexylamine followed by permethylation was used as a procedure for the liquid secondary ion mass spectrometry (LSIMS) analysis of Asn-linked oligosaccharides. Initial experiments with this procedure were performed on maltoheptaose. These experiments show that exhaustive methylation at the newly formed secondary nitrogen forms a quaternary ammonium salt. When this is subjected to positive ion LSIMS, an abundant M(+) ion is observed. This procedure was applied to the Asn-linked oligosaccharides released from human transferrin and ribonuclease-B. The reductively aminated, permethylated mixture of oligosaccharides from ribonuclease-B afforded a positive ion LSI mass spectrum in which M(+) ions for Mans5-9GlcNAc2 could be assigned. The positive ion LSI mass spectrum obtained from the mixture of oligosaccharides isolated from human transferrin showed M(+) ions that could be assigned to both monosialylated and disialylated biantennary complex type oligosaccharides. Reductive amination followed by permethylation of the Asn-linked oligosaccharides isolated from baculovirus expressed mouse interleukin-3 produced in Bombyx mori gave a positive ion LSI mass spectrum in which the oligosaccharides could be assigned the monosaccharide composition Man2-4[Fuc]GlcNAc2 and Man2GlcNAc2. These are believed to be dimannose, trimannose, and tetramannose chitobiose core oligosaccharides, three of which are fucosylated.

Carbohydrate structure of a thrombin-like serine protease from Agkistrodon rhodostoma. Structure elucidation of oligosaccharides by methylation analysis, liquid secondary-ion mass spectrometry and proton magnetic resonance

The carbohydrate side chains of the thrombin-like serine protease ancrod from the venom of the Malayan pit viper Agkistrodon rhodostoma were liberated from tryptic glycopeptides by treatment with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F and fractionated by high-performance liquid chromatography. Glycans obtained were characterized by digestion with exoglycosidases, methylation analysis and, in part, by liquid secondary-ion mass spectrometry and 1H-NMR spectroscopy. The results reveal that this snake venom glycoprotein contains partially truncated di-, tri- and tetraantennary complex type N-glycans carrying Fuc(alpha 1-6) residues at the innermost N-acetylglucosamine and solely (alpha 2-3)-linked sialic acid substituents. As a characteristic feature, ancrod oligosaccharides comprise mainly sialylated Gal beta 3GlcNAc beta lactosamine antennae. Furthermore, a small proportion of the sugar chains were found to carry a NeuAc alpha 3GalNAc beta 4GlcNAc beta antenna exclusively linked to C-2 of Man(alpha 1-3) residues of the pentasaccharide core. Thus, many of the glycans found represent novel glycoprotein-N-glycan structures.

Characterization of seven xyloglucan oligosaccharides containing from seventeen to twenty glycosyl residues

The complete primary structures of seven oligosaccharide subunits of the xyloglucan secreted by suspension-cultured Acer pseudoplatanus cells were determined. The oligosaccharides, ranging in size from 17 to 20 glycosyl residues, were generated by treatment of the xyloglucan with an endo-beta-(1----4)-glucanase. The oligosaccharide components of a fraction obtained by Bio-Gel P-2 chromatography of enzyme-treated xyloglucan were further purified by normal-phase h.p.l.c. and then converted to the corresponding oligoglycosyl alditols by reduction with NaBH4. The oligoglycosyl alditols, after purification to near homogeneity by reversed-phase h.p.l.c., were structurally characterized by 1H-n.m.r. spectroscopy, fast-atom bombardment mass spectrometry (f.a.b.-m.s.), and analysis of their glycosyl-residue and glycosyl-linkage compositions. Novel structural elements of xyloglucans were observed in this study, including beta-D-xylopyranosyl and alpha-L-arabinofuranosyl-(1----3)-beta-D-xylopyranosyl sidechains. The results also extend our list of correlations between 1H-n.m.r. resonances and specific structural features of xyloglucans and thus enhance our ability to determine the structures of xyloglucans from various sources.

Extended type-1 chain glycosphingolipid antigens. Isolation and characterization of trifucosyl-Leb antigen (III4V4VI2Fuc3Lc6)

A Lewis-b-active glycosphingolipid containing a repetitive type-1 chain carbohydrate core was isolated from human colonic adenocarcinoma cell line Colo205. This glycosphingolipid was purified by HPLC and preparative high-performance thin-layer chromatography and its structure elucidated by positive-ion fast-atom-bombardment mass spectrometry with collision-induced disassociation, 1H-NMR spectroscopy and methylation analysis. The glycosphingolipid was found to be a trifucosylated derivative of this novel carbohydrate core, having the following structure: [formula; see text].

Production and characterization of a monoclonal antibody (BBH5) directed to ganglioside lactone

The occurrence of lactones in various ganglioside preparations has been clearly demonstrated, yet the natural occurrence of ganglioside lactones in cells and tissues has been the subject of long debate, since lactones can be formed readily during preparation of gangliosides. We now report the generation of monoclonal antibody (BBH5) that reacts specifically with lactones of disialogangliosides having the NeuAc2-8NeuAc2-3Gal sequence, but does not crossreact with the parent ganglioside. The specificity of the antibody resides on the first lactone ring between two sialic acid residues but not on the second lactone ring between sialic acid and galactose, as evidenced by reactivity with lactonized GD1b having the first lactone ring (L1), and by reactivity with lactonized polysialic acid homo-oligomers ([NeuAc alpha 2-8]nNeuAc). The sialic acid carboxyl involved in the lactone ring was unequivocally determined after ammonolysis followed by methylation and fast atom bombardment mass spectrometry. The antibody BBH5 thus provides a novel tool for studies of the natural occurrence of lactones in cells and tissues.

Complex carbohydrates in drug development

Recent advances in carbohydrate chemistry and biochemistry afford the opportunity to develop bioactive complex carbohydrates, per se , as drugs or as lead compounds in drug development. Complex carbohydrates are unique among biopolymers in their inherent potential to generate diverse molecular structures. While proteins vary only in the linear sequence of their monomer constituents, individual monosaccharides can combine at any of several sites on each carbohydrate ring, in linear or branched arrays, and with varied stereochemistry at each linkage bond. This chapter addresses some salient features of mammalian glycoconjugate structure and biosynthesis, and presents examples of the biological activities of complex carbohydrates. The chapter presents selected examples that will provide an accurate introduction to their pharmacological potential. In addition to their independent functions, oligosaccharides can modify the activities of proteins to which they are covalently attached. Many glycoprotein enzymes and hormones require glycosylation for expression and function. The chapter discusses the ancillary role of carbohydrates that is of great importance to the use of engineered glycoproteins as pharmaceuticals.

Molecular basis of symbiotic host specificity in Rhizobium meliloti: nodH and nodPQ genes encode the sulfation of lipo-oligosaccharide signals

The symbiosis between Rhizobium and legumes is highly specific. For example, R. meliloti elicits the formation of root nodules on alfalfa and not on vetch. We recently reported that R. meliloti nodulation (nod) genes determine the production of acylated and sulfated glucosamine oligosaccharide signals. We now show that the biochemical function of the major host-range genes, nodH and nodPQ, is to specify the 6-O-sulfation of the reducing terminal glucosamine. Purified Nod factors (sulfated or not) from nodH+ or nodH- strains exhibited the same plant specificity in a variety of bioassays (root hair deformations, nodulation, changes in root morphology) as the bacterial cells from which they were purified. These results provide strong evidence that the molecular mechanism by which the nodH and nodPQ genes mediate host specificity is by determining the sulfation of the extracellular Nod signals.

Characterisation of the N-linked oligosaccharides of the light chain of human glycoprotein IIb by f.a.b.-m.s

The glycosylation of the light chain (GPIIbL) of glycoprotein IIb, one of the glycoproteins constituting the receptor for fibrinogen, fibronectin, and the von Willebrand factor on platelet cell surfaces, was investigated using fast-atom-bombardment mass spectrometry (f.a.b.-m.s.). Complex-type N-glycans were observed, attached to Asn-60. The most abundant oligosaccharide is a disialylated biantennary structure substituted with fucose on the chitobiose core. Mono-sialylated biantennary, and di- and tri-sialylated triantennary structures were found as minor constituents of the N-glycan population. The amino acid sequence of GPIIbL was fully mapped by f.a.b.-m.s., thereby providing the first direct evidence for the absence of O-glycosylation.

Non-reducing terminal linkage position determination in intact and permethylated synthetic oligosaccharides having a penultimate amino sugar: fast atom bombardment ionization, collisional-induced dissociation and tandem mass spectrometry

Certain linkage positions in oligosaccharides can be discerned by collision-activated dissociation mass spectrometry, rationalized by molecular modelling. Previous work on synthetic oligosaccharides has suggested that daughter ion patterns can distinguish among intact compounds which terminate in alpha-L-fucose and have a penultimate amino sugar. The current study indicates that these observations can be extended to oligosaccharides terminating in beta-D-galactose. In addition, we have observed that protonated, ammoniated and lithiated molecular ions all produce linkage-specific daughter ion spectra in these two sets of oligosaccharides. Sodiated molecular ions could be fragmented usefully under high collision energy offset conditions; potassiated ions were stable and not dissociable under conditions available in a triple-quadrupole instrument. We also show linkage discernment among the permethylated set of these six synthetic oligosaccharides. Methylated derivatives of this set of compounds give more useful product ions, including a 3-linkage specific ion. A novel relationship was noted by a plot of collision energy against (daughter ion/parent ion) ratio, which gave a unique slope for each of the non-reducing terminal linkage positions 3, 4 and 6 in the set of six compounds. The slope of this plot is related to the ability of each linkage position in the oligosaccharide to absorb collisional energy. Rotational freedom of the individual glycosidic linkage is hypothesized to play a role in this phenomenon.

Structural studies of the Vibrio cholerae O:3 O-antigen polysaccharide

The structure of the Vibrio cholerae O:3 O-antigen polysaccharide has been investigated, mainly by n.m.r. spectroscopy, mass spectrometry, sugar and methylation analysis, and specific degradations, and is proposed to involve the following tetrasaccharide repeating-unit. [formula: see text]. In this structure, D-D-Hep is D-glycero-D-manno-heptose, Asc is 3,6-dideoxy-L-arabino-hexose (ascarylose), and Sug is 2,4-diamino-2,4,6-trideoxy-D-glucose (bacillosamine) in which N-2 is acetylated and N-4 is acylated with a 3,5-dihydroxyhexanoic acid. That the 2,4-diamino-2,4,6-trideoxy-D-glucose residue is linked through O-3 and not through one of the hydroxyl groups in the 3,5-dihydroxyhexanoyl group is indicated but not definitely proved. The configuration of the latter group has not been determined. The f.a.b.-mass spectrum of the methylated O-antigen indicates that the structure given above also represents the biological repeating-unit.

Glucan synthesis in Pneumocystis carinii

Rat-derived Pneumocystis carinii lysed with sodium deoxycholate catalysed the incorporation of uridine diphosphoglucose into an insoluble polymer. This enzyme activity was present in both the pellet and the supernatant when the P. carinii preparations were centrifuged. The polymer whose production was catalysed by the supernatant was examined by mass spectrometry and found to be an alpha 1----4 glucan, which is either unbranched or has relatively few branches. Polymer formation was completely inhibited by the addition of alpha amyloglucohydrolase to the supernatant. Polymer formation in the pellet of deoxycholate P. carinii preparations, unlike that in the supernatant, was partially resistant to alpha amyloglucohydrolase. The soluble glucan synthase activity in the supernatant was stable for more than 30 h at room temperature and was approximately 50 times more active on a cell-to-cell basis than the supernatant from deoxycholate preparations of the yeast Saccharomyces cerevisae.

The analysis of underivatized oligosaccharides by matrix-assisted laser desorption mass spectrometry

Matrix Assisted Laser Desorption Mass Spectrometry is shown to provide a rapid and sensitive technique for the analysis of underivatized oligosaccharides. Typical sample loading is 1 pmol and analysis time is around 5 minutes. Through the use of an internal standard, mass measurements are generally accurate to within 0.5 Da. The technique is particularly useful for the analysis of oligosaccharide mixtures released from glycoproteins.

n-Alkyl p-aminobenzoates as derivatizing agents in the isolation, separation, and characterization of submicrogram quantities of oligosaccharides by liquid secondary ion mass spectrometry

In this laboratory we are pursuing a comprehensive strategy for isolation and characterization of oligosaccharides from glycoproteins that are available only in limited quantities. To improve sensitivity in the analysis by liquid secondary ion mass spectrometry, we have investigated the relative behavior of a homologous series of n-alkyl esters of p-aminobenzoic acid as derivatizing agents. Ethyl p-aminobenzoate, the derivatizing agent used in many of our earlier studies, is one of these compounds. Our experiments using the hepatasaccharide maltoheptaose (M7) as a model oligosaccharide establish that by lengthening the alkyl chain from methyl to n-tetradecyl, a concomitant increase in the molecular ion abundance is obtained. The increase is a factor of 10 when 1 microgram of derivatized M7 is analyzed, and as much as 40 when 0.1 microgram of sample is examined. This series of derivatives of maltoheptaose form a suite of relatively abundant fragment ions in the negative ion mode as expected from our previous studies with the ethyl ester. Although very high mass spectral sensitivities were achieved with M7 n-tetradecyl and n-decyl p-aminobenzoates, the yields of derivative obtained were significantly lower than those obtained for M7 n-octyl, n-hexyl, n-butyl, ethyl, and methyl p-aminobenzoates, despite improvements made in the derivatization procedure. When analyzing biological samples, n-octyl and n-hexyl p-aminobenzoate were found to be optimal considering both yield of derivative and mass spectral sensitivity. This improved method of derivatization was incorporated into a simple but effective procedure for dealing with very small quantities of heterogeneous samples of oligosaccharides, such as those released from 250 micrograms (1 nmol) of nicotinic acetylcholine receptor from Torpedo californica and 90 micrograms (2 nmol) of human alpha 1 acid glycoprotein.

Oligosaccharide sequence determination using B/E linked field scanning or tandem mass spectrometry of phosphatidylethanolamine derivatives

Product ion mass spectral data of [M + H]+ ions of oligosaccharides, mainly tetra- and pentasaccharides, as their dipalmitoyl phosphatidylethanolamine derivatives were obtained using both liquid secondary ion mass spectrometry with B/E linked scanning and fast atom bombardment ionization with collision-induced dissociation/tandem mass spectrometry. Both methods give similar positive product ion spectra of equivalent high sensitivity (detection limits of approximately 50 pmol) that principally contain glycosidic cleavage ions retaining the reducing end of the molecule from which monosaccharide sequence can be deduced. A series of ions from fission of the phosphate ester bond together with glycosidic cleavage are present in the tandem mass spectra and B/E linked scan spectra when helium collision gas is used. Monosaccharide linkage position of isomeric molecules is reflected in the intensity of glycosidic fragmentation, without retention of the oxygen atom, with decreasing cleavage in the order 1-3 greater than 1-4 greater than 1-6 linkage. Fucose and N-acetylhexosamines show an increased degree of fragmentation over hexose sugars. The application of product ion spectra of derivatized oligosaccharides is demonstrated for characterizing mixed samples and also the acquisition of spectra directly from the silica surface of high-performance thin-layer chromatography plates.

A new undecasaccharide subunit of xyloglucans with two alpha-L-fucosyl residues

A new oligosaccharide subunit of xyloglucan was isolated from the beta-(1----4)-endoglucanase digestion products of the xyloglucan in what is referred to as "sycamore extracellular polysaccharides" and found to be an undecasaccharide having two terminal alpha-L-fucopyranosyl residues. The undecasaccharide was structurally characterized by 1H-n.m.r. spectroscopy, fast-atom bombardment mass spectrometry (f.a.b.-m.s.), and glycosyl-residue and glycosyl-linkage composition analyses. The structure of the undecasaccharide was confirmed by digesting it with a hydrolase that releases alpha-D-Xylp-(1----6)-D-Glc from the non-reducing end of xyloglucan oligosaccharides.

Fast-atom-bombardment mass spectrometry of sulphated oligosaccharides from ovine lutropin

The positive- and negative-ion f.a.b.-mass spectra and the fragmentation of sulphated oligosaccharides derived from ovine lutropin are described. Negative-ion f.a.b.-m.s. of methylated derivatives offers a sensitive and rapid method for screening glycans for sulphation, for defining the location of sulphated residues, and for sequencing sulphated branches. Positive-ion f.a.b.-m.s. gives complementary data on non-sulphated branches in both complex and hybrid-type sulphated structures.

Structural classification of carbohydrates in glycoproteins by mass spectrometry and high-performance anion-exchange chromatography

A general strategy has been developed for determining the structural class (oligomannose, hybrid, complex), branching types (biantennary, triantennary, etc.), and molecular microheterogeneity of N-linked oligosaccharides at specific attachment sites in glycoproteins. This methodology combines mass spectrometry and high-performance anion-exchange chromatography with pulsed amperometric detection to take advantage of their high sensitivity and the capability for analysis of complex mixtures of oligosaccharides. Glycopeptides are identified and isolated by comparative HPLC mapping of proteolytic digests of the protein prior to, and after, enzymatic release of carbohydrates. Oligosaccharides are enzymatically released from each isolated glycopeptide, and the attachment site peptide is identified by fast atom bombardment mass spectrometry (FAB-MS) of the mixture. Part of each reaction mixture is then permethylated and analyzed by FAB-MS to identify the composition and molecular heterogeneity of the carbohydrate moiety. Fragment ions in the FAB mass spectra are useful for detecting specific structural features such as polylactosamine units and bisecting N-acetylhexosamine residues, and for locating inner-core deoxyhexose residues. Methylation analysis of these fractions provides the linkages of monomers. Based on the FAB-MS and methylation analysis data, the structural classes of carbohydrates at each attachment site can be proposed. The remaining portions of released carbohydrates from specific attachment sites are preoperatively fractionated by high-performance anion-exchange chromatography, permethylated, and analyzed by FAB-MS. These analyses yield the charge state and composition of each peak in the chromatographic map, and provide semiquantitative information regarding the relative amounts of each molecular species. Analytically useful data may be obtained with as little as 10 pmol of derivatized carbohydrate, and fmol sensitivity has been achieved. The combined carbohydrate mapping and structural fingerprinting procedures are illustrated for a recombinant form of the CD4 receptor glycoprotein.