A high-performance liquid chromatography method for the analysis of picomole amounts of oligosaccharides

Molecular directionality of polysaccharide polymerization by the Pasteurella multocida hyaluronan synthase

Hyaluronan (HA), a long linear polymer composed of alternating glucuronic acid and N-acetylglucosamine residues, is an essential polysaccharide in vertebrates and a putative virulence factor in certain microbes. All known HA synthases utilize UDP-sugar precursors. Previous reports describing the HA synthase enzymes from Streptococcus bacteria and mammals, however, did not agree on the molecular directionality of polymer elongation. We show here that a HA synthase, PmHAS, from Gram-negative P. multocida bacteria polymerizes the HA chain by the addition of sugar units to the nonreducing terminus. Recombinant PmHAS will elongate exogenous HA oligosaccharide acceptors to form long polymers in vitro; thus far no other HA synthase has displayed this capability. The directionality of synthesis was established definitively by testing the ability of PmHAS to elongate defined oligosaccharide derivatives. Analysis of the initial stages of synthesis demonstrated that PmHAS added single monosaccharide units sequentially. Apparently the fidelity of the individual sugar transfer reactions is sufficient to generate the authentic repeating structure of HA. Therefore, simultaneous addition of disaccharide block units is not required as hypothesized in some recent models of polysaccharide biosynthesis. PmHAS appears distinct from other known HA synthases based on differences in sequence, topology in the membrane, and putative reaction mechanism.

The analysis of fluorophore-labeled carbohydrates by polyacrylamide gel electrophoresis

The glycans of glycoconjugates mediate numerous important biological processes. Their separation and structural determination present considerable difficulties because of the small quantities that are available from biological sources and the inherent difficulty of analyzing the wide variety of complex structures that exist. A method for the analysis of reducing saccharides by PAGE that uses specific fluorophore labeling and is simple, rapid, sensitive, and readily available to biological researchers, has been developed. This method is known acronimically either as PAGEFS (PAGE of Fluorophore-labeled Saccharides) or in one commercial format as FACE (Fluorophore-Assisted Carbohydrate Electrophoresis). In the PAGEFS method, saccharides having an aldehydic reducing end group are labeled quantitatively with a fluorophore and then separated with high resolution by PAGE. Two fluorophores, 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS) and 2-aminoacridone (AMAC), have been used to enable the separation of a variety of saccharide positional isomers, anomers, and epimers. Subpicomolar quantities of individual saccharides can be detected using a sensitive imaging system. Mixtures of oligosaccharides obtained by enzymatic cleavage from glycoproteins can be labeled and electrophoresed to yield an oligosaccharide profile of each protein. AMAC can be used to distinguish unequivocally between acidic and neutral oligosaccharides. Methods of obtaining saccharide sequence information from purified oligosaccharides have been developed using enzymatic degradation. Other applications and the potential of the system are described.

Determination of beta-(1-3),(1-4)-D-glucans in barley by reversed-phase high-performance liquid chromatography

An HPLC method for the determination of beta-glucan in barley was developed. The beta-glucan was hydrolysed with lichenase [endo-beta-(1-3),(1-4)-D-glucan-4-glucanhydrolase from Bacillus subtilis] to oligosaccharides, which were analysed by reversed-phase HPLC using water as the mobile phase at a flow-rate of 0.7 ml/min. The separation of the oligosaccharides was performed in a C18 stainless-steel column (Spherisorb ODS-2) with 5-microns particles in less than 10 min, with a refractive index detection.

The structural basis of the inhibition of human alpha-mannosidases by azafuranose analogues of mannose

Eight pyrrolidine, five pyrrolizidine and one indolizidine analogue(s) of the known alpha-mannosidase inhibitor, the azafuranose, 1,4-dideoxy-1,4-imino-D-mannitol (DIM), have been tested for inhibition of the multiple forms of alpha-mannosidase in human liver in vitro. Substitution of the ring nitrogen markedly decreased or abolished inhibition, but loss of the C-6 hydroxy group, as in 6-deoxy-DIM and 6-deoxy-6-fluoro-DIM, enhanced inhibition, particularly of the lysosomal alpha-mannosidase. Addition of the anomeric substituent-CH2OH decreased inhibition. To be a potent inhibitor of the lysosomal, Golgi II and neutral alpha-mannosidases, a polyhydroxylated pyrrolidine must have the same substituents and chirality as mannofuranose at C-2, C-3, C-4 and C-5. These four chiral centres can also be part of a polyhydroxylated indolizidine, e.g. swainsonine, but not of a pyrrolizidine, e.g. cyclized DIM, ring-contracted swainsonine or 1,7-diepi-australine. DIM did not inhibit lysosomal alpha-mannosidase intracellularly, but both 6-deoxy-DIM and 6-deoxy-6-fluoro-DIM caused accumulation of partially catabolized glycans in normal human fibroblasts. Analysis of these induced storage products by h.p.l.c. showed that both compounds also inhibited Golgi alpha-mannosidase II and that 6-deoxy-6-fluoro-DIM was also a good inhibitor of the endoplasmic reticulum alpha-mannosidase and specific lysosomal alpha (1-6)-mannosidase. None of the mannofuranose analogues appeared to inhibit Golgi alpha-mannosidase I.

A comprehensive procedure for preparation of partially methylated alditol acetates from glycoprotein carbohydrates

Various steps involved in the preparation of partially methylated alditol acetates (PMAAs) from glycoprotein-derived carbohydrates were improved to obtain the derivatives in a rapid manner with excellent yields. Carbohydrates were permethylated in dimethyl sulfoxide (DMSO), using a fine suspension of sodium hydroxide and methyl iodide (CH3I). The fine suspension of NaOH was prepared conveniently from commercially available 50% aqueous NaOH in DMSO by sonication and washing the precipitate with DMSO. Methylation of ovalbumin and fetuin glycopeptides using the fine suspension of NaOH and CH3I was complete within 5 min, and the methylation reaction did not generate any nonsugar artifacts. Methylated carbohydrates without any purification were hydrolyzed in a mixture of volatile organic acids, which permitted rapid removal of the acids from samples by evaporation. Acetylation of partially methylated alditols with acetic anhydride for 2-4 h at ambient temperature using 4-N,N'-dimethylaminopyridine as a catalyst and the reaction was free from generating nonsugar reaction artifacts. The reaction time course for methylation, hydrolysis, and acetylation was determined to obtain optimum reaction conditions for preparation of the PMAAs. The procedure facilitated rapid identification and quantitation of PMAAs due to diminished reaction artifacts and the quality of the chromatogram depended only on the purity of starting material and the reagents used for the methylation analysis. Utility of these simple methods for rapid methylation analysis was demonstrated in the characterization of oligosaccharides isolated in small amounts using a carbohydrate analyzer.

Stored dolichyl pyrophosphoryl oligosaccharides in Batten disease

Each of the 3 childhood forms of Batten disease, juvenile (JB), late-infantile (LIB), and infantile (IB), have abnormally high brain concentrations of dolichyl pyrophosphoryl oligosaccharides (Dol-PP-OS). In this study, the carbohydrate portions of Dol-PP-OS were analysed: in JB and LIB, they range in size from Man2GlcNAc2 to Glc3Man9GlcNAc2, predominant components being Man5-7GlcNAc2 and Glc3Man7GlcNAc2. In IB, they range from Man6-9GlcNAc2, no glucose containing oligosaccharides being identified. In Batten disease, the main subcellular location of Dol-PP-OS is within storage material, where it represents up to 7% of the dry weight. [3H]-Mannose incorporation experiments with cultured fibroblasts show that synthesis of Dol-PP-OS in JB is normal. We infer that the glycosylation intermediate Glc3Man9GlcNAc2-PP-dolichol is synthesised normally within the endoplasmic reticulum in Batten disease, but that catabolic derivatives accumulate within the lysosomes. It is unclear whether this process is central to the pathogenesis of the disease, though in IB a defect in the release of mannose residues from Dol-PP-OS is a distinct possibility.

The substrate-specificity of human lysosomal alpha-D-mannosidase in relation to genetic alpha-mannosidosis

The specificity of human liver lysosomal alpha-mannosidase (EC 3.2.1.24) towards a series of oligosaccharide substrates derived from high-mannose, complex and hybrid asparagine-linked glycans and from the storage products in alpha-mannosidosis was investigated. The enzyme hydrolyses all alpha(1-2)-, alpha(1-3)- and alpha(1-6)-mannosidic linkages in these glycans without a requirement for added Zn2+, albeit at different rates. A major finding of this study is that all the substrates are hydrolysed by non-random pathways. These pathways were established by determining the structures of intermediates in the digestion mixtures by a combination of h.p.t.l.c. and h.p.l.c. before and after acetolysis. The catabolic pathway for a particular substrate appears to be determined by its structure, raising the possibility that degradation occurs by an uninterrupted sequence of steps within one active site. The structures of the digestion intermediates are compared with the published structures of the storage products in mannosidosis and of intact asparagine-linked glycans. Most but not all of the digestion intermediates derived from high-mannose glycans have structures found in intact asparagine-linked glycans of human glycoproteins or among the storage products in the urine of patients with mannosidosis. However, the relative abundances of these structures suggests that the catabolic pathway is not the same as the processing pathway. In contrast, the intermediates formed from the digestion of oligosaccharides derived from hybrid and complex N-glycans are completely different from any processing intermediates and also from the oligosaccharides of composition Man2-4GlcNAc that account for 80-90% of the storage products in alpha-mannosidosis. It is postulated that the structures of these major storage products arise from the action of an exo/endo-alpha(1-6)-mannosidase on the partially catabolized oligomannosides that accumulate in the absence of the main lysosomal alpha-mannosidase.

Analysis of mucin-derived oligosaccharides by medium-pressure gel-permeation and amino-plate thin-layer chromatography conducted in conjunction

Oligosaccharides present in mucin were labeled by reduction with NaB3H4 and separated by gel-permeation chromatography with a Toyopearl HW-40S column using 0.1 M pyridine acetate, pH 5.0, as the solvent. Each fraction was further analyzed by thin-layer chromatography (TLC) on a Funagel AMP plate, a glass plate precoated with 3-aminopropyl-bonded silica. Acetonitrile/10 mM triethylamine acetate (3/2, by volume) served as the solvent. The sites of oligosaccharides on the TLC plate could be determined according to size, anionic charge, and sugar composition. They could thus be "mapped" on the plate. In this manner, the distribution of oligosaccharides on bovine submaxillary mucin and rat gastric mucin was determined. Each radiolabeled oligosaccharide in newly synthesized rat gastric mucin, metabolically labeled with [14C]glucosamine or [35S]sulfate, was also identified by this method.

Glycoconjugates in storage cytosomes from ceroid-lipofuscinosis (Batten's disease) and in lipofuscin from old-age brain

The ceroid-lipofuscinoses (CL) are a group of inherited diseases characterised by the accumulation, in brain, of autofluorescent storage cytosomes which have similar histochemical staining properties to lipofuscin, the neuronal wear and tear pigment of old-age brain. The storage cytosomes stain strongly with periodic acid-Schiff reagent (PAS), indicating the presence of carbohydrate. In brain from each childhood form of CL, concentrations of phosphorylated dolichol (Dol-P) are 10- to 20- fold higher than in age-matched controls. Brain Dol-P concentrations are also increased between 2 and 5- fold in several different lipidoses and in elderly subjects. Much of the Dol-P which accumulates is located within the storage cytosomes. Dol-P constitutes 2-3% of the dry weight of storage cytosomes from juvenile and late-infantile CL, and 0.3-0.7% of storage cytosomes from infantile CL, ovine CL and of lipofuscin isolated from old age brain. The bulk of the Dol-P in CL brain and in isolated storage cytosomes is present as dolichyl pyrophosphoryl oligosaccharides (Dol-PP-OS). The constitutions of the oligosaccharide moieties differ in the various forms of the disease. Histochemical analysis of frozen sections of unfixed brain after extraction by various lipid solvents indicates that the major part of the PAS positive intraneuronal material in CL brain and in old-age brain has the extraction properties of Dol-PP-OS. Carbohydrate represents 4-7% of the dry weight of CL storage cytosomes and of lipofuscin. The major monosaccharide components are mannose, N-acetyl glucosamine, glucose and galactose. Depending on the form of the disease studied, up to 40% of this material can be accounted for by Dol-PP-OS. Polyacrylamide gel electrophoresis of storage cytosomes followed by lectin blotting demonstrates several low molecular weight components which bind concanavalin A. These do not coelute with the major protein components and may well be Dol-PP-OS. We conclude that Dol-PP-OS are concentrated in storage cytosomes in CL and are one of their major glycoconjugate components.

Analysis of dolichyl pyrophosphoryl oligosaccharides in purified storage cytosomes from ovine ceroid-lipofuscinosis

Ovine ceroid-lipofuscinosis is an inherited neurodegenerative disorder characterised by the accumulation of storage cytosomes in brain and visceral organs. Phosphorylated dolichol-containing compounds, largely in the form of dolichyl pyrophosphoryl oligosaccharides, have been shown to constitute 1-2% of the dry weight of storage cytosomes isolated from brain and pancreas, and 0.5 and 0.1% respectively of storage cytosomes isolated from liver and kidney. The carbohydrate portion of these glyconjugates in storage cytosomes isolated from brain, pancreas and liver consisted of a series of oligosaccharides of composition Man2-9GlcNAc2, with Man5-8GlcNAc2 predominating. The concentrations of dolichyl pyrophosphoryl oligosaccharides in storage cytosomes from ovine ceroid-lipofuscinosis are much higher than has been reported for endoplasmic reticulum, their normal functional location.