Mild alkaline borohydride treatment of glycoproteins-a method for liberating both N- and O-linked carbohydrate chains

Simultaneous assay of pigments, carbohydrates, proteins and lipids in microalgae

Biochemical compositional analysis of microbial biomass is a useful tool that can provide insight into the behaviour of an organism and its adaptational response to changes in its environment. To some extent, it reflects the physiological and metabolic status of the organism. Conventional methods to estimate biochemical composition often employ different sample pretreatment strategies and analytical steps for analysing each major component, such as total proteins, carbohydrates, and lipids, making it labour-, time- and sample-intensive. Such analyses when carried out individually can also result in uncertainties of estimates as different pre-treatment or extraction conditions are employed for each of the component estimations and these are not necessarily standardised for the organism, resulting in observations that are not easy to compare within the experimental set-up or between laboratories. We recently reported a method to estimate total lipids in microalgae (Chen, Vaidyanathan, Anal. Chim. Acta, 724, 67-72). Here, we propose a unified method for the simultaneous estimation of the principal biological components, proteins, carbohydrates, lipids, chlorophyll and carotenoids, in a single microalgae culture sample that incorporates the earlier published lipid assay. The proposed methodology adopts an alternative strategy for pigment assay that has a high sensitivity. The unified assay is shown to conserve sample (by 79%), time (67%), chemicals (34%) and energy (58%) when compared to the corresponding assay for each component, carried out individually on different samples. The method can also be applied to other microorganisms, especially those with recalcitrant cell walls.

Negative ion CID fragmentation of O-linked oligosaccharide aldoses--charge induced and charge remote fragmentation

Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H](-) ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H](-) ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H](2-) ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the (0,2)A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.

Asparaginylglucose: Novel type of carbohydrate linkage

The Halobacterial cell wall glycoprotein was recently shown to contain two types of sulfated saccharides: a repetitive saccharide and a nonrepetitive saccharide composed of glucuronic acid and glucose. A new type of N-glycosidic linkage is found in this latter type of saccharide: glucose is N-glycosidically linked to the polypeptide chain through the amido nitrogen of an asparagine residue, as shown by chemical analyses, proton magnetic resonance spectroscopy, and mass spectroscopy of an isolated asparaginyl saccharide. The only N-glycosidic linkage known so far is between the amido nitrogen of asparagine and N-acetylglucosamine.

Development of a robust and high throughput method for profiling N-linked glycans derived from plasma glycoproteins by NanoLC-FTICR mass spectrometry

Recent investigations continue to emphasize the importance of glycosylation in various diseases including cancer. In this work, we present a step-by-step protocol describing a method for N-linked glycan profiling of plasma glycoproteins by nanoflow liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). A large experimental space was initially explored and is described herein. Three internal standards were spiked into the sample and provided normalization of plasma glycan abundance across different experimental conditions. Incubation methods and times and the effect of NP40 detergent on glycan abundance were explored. It was found that an 18-h incubation with no detergent led to the greatest ion abundance; however, data could be obtained in less than one day from raw plasma samples utilizing microwave irradiation or shorter incubation periods. The intersample precision of three different glycans was less than 5.5% (RSD) when the internal standards were added prior to the initial processing step. The high mass measurement accuracy (<3 ppm) afforded by the FTICR mass spectrometer provided confident identifications of several glycan species.

Development of a nanoLC LTQ orbitrap mass spectrometric method for profiling glycans derived from plasma from healthy, benign tumor control, and epithelial ovarian cancer patients

We report the development of split-less nano-flow liquid chromatography mass spectrometric analysis of glycans chemically cleaved from glycoproteins in plasma. Porous graphitized carbon operating under reverse-phase conditions and an amide-based stationary phase operating under hydrophilic interaction conditions are quantitatively compared for glycan separation. Both stationary phases demonstrated similar column efficiencies and excellent retention time reproducibility without an internal standard to correct for retention time shift. The 95% confidence intervals of the mean retention times were +/-4 s across 5 days of analysis for both stationary phases; however, the amide stationary phase was observed to be more robust. The high mass measurement accuracy of less than 2 ppm and fragmentation spectra provided highly confident identifications along with structural information. In addition, data are compared among samples derived from 10 healthy controls, 10 controls with a differential diagnosis of benign gynecologic tumors, and 10 diseased epithelial ovarian cancer patients (EOC). Two fucosylated glycans were found to be up-regulated in healthy controls and provided an accurate diagnostic value with an area under the receiver operator characteristic curve of 0.87. However, these same glycans provided a significantly less diagnostic value when used to differentiate EOC from benign tumor control samples with an area under the curve of 0.73.

Aminopeptidases and proteolipids of intestinal brush border

The presence of human blood group A determinants has been shown on the A+ rabbit intestinal brush border glycoproteins, particularly hydrolases. Sugar compositions of aminopeptidases N from A+ and A- rabbits were compatible with the presence in these molecules of eight N-linked glycans and of two O-linked glycans bearing the A determinants in A+ animals. The exact relative molecular masses of hydrophobic domain(s) of aminopeptidases N and A from pig and rabbit intestinal brush border have been determined by an isotopic dilution technique. The values obtained were compatible with the anchorage in the membrane of the monomeric rabbit enzymes, or of each subunit of the dimeric pig enzymes, by their N-terminal sequences, composed of 20-25 hydrophobic amino acids. This N-terminal hydrophobic sequence (14 residues) has been determined for rabbit aminopeptidase N. Short peptides containing approximately 60% hydrophobic amino acids have been extracted by chloroform-methanol from purified brush border and basolateral membranes of pig enterocytes. Their molecular properties were very similar to those of the aminopeptidase anchors released by trypsin treatment of detergent-extracted enzymes. However, several lines of evidence failed to support the assumption that these free hydrophobic peptides can be identified with anchors left inside the bilayer after proteolytic cleavage of surface hydrolases.

Beta-elimination for release of O-linked glycosaminoglycans from proteoglycans

O-linked glycosaminoglycan (GAG) chains in proteoglycans are readily released from their core proteins by treatment with alkali at room temperature. This beta-elimination is the same type of reaction as that for releasing O-linked oligosaccharides from their core proteins. Under the reaction conditions described here, N-linked oligosaccharides remain attached to the core protein, but any O-linked oligosaccharides will be released along with the GAG chains. The procedure can be used to isolate the free GAG chains, the free O-linked oligosaccharides, and the core protein (which will still have any N-linked oligosaccharides that were originally present).

Beta-elimination for release of O-GalNAc-linked oligosaccharides from glycoproteins and glycopeptides

This unit describes release of oligosaccharides that are attached to polypeptides through an N-acetylgalactosamine (GalNAc) linkage to the hydroxyl groups of serine or threonine. The beta-elimination procedures described here can be used to recover the oligosaccharide chains (also called glycans) and/or identify the serine or threonine residues involved in the linkage. A beta-elimination method employing sodium borohydride (NaBH4) and alkaline conditions is described, and an alternative method is also presented in which only alkaline conditions are used without a reducing agent. Another alternative protocol uses sodium sulfite.

Challenges in the expression of disulfide bonded, threonine-rich antifreeze proteins in bacteria and yeast

Certain freeze-intolerant insects produce antifreeze proteins (AFPs) during overwintering including the spruce budworm (Choristoneura fumiferana) and yellow mealworm (Tenebrio molitor) AFP gene families. However, only a few of the isoforms, encoded by their multiple-copy gene families, have been characterized. When expressed in bacterial systems the insect AFPs have to be denatured and refolded in vitro, a procedure that is not uniformly successful, presumably due to the beta-helix structure and the requirement for disulfide bonds. In an attempt to overcome these difficulties, bacterial vectors and hosts that have been developed to produce soluble, folded proteins, as well as a yeast expression system (Pichia pastoris) were employed. Bacterial expression resulted in low quantities of active recombinant protein for certain isoforms. In contrast, both small and large-scale fermentation of recombinant AFP in Pichia yielded substantial protein production (100 mg/L) but functional ice binding activity of protein produced in three different transformed yeast strains (KM71, X33 or GS115) was low. Inappropriate O-linked glycosylation of the Thr-rich AFPs appeared to be partially reversed by mild chemical deglycosylation, but activity remained low. Substantial quantities, as well as activity were recovered when a fish AFP, with disulfide bonds, but without potential Thr glycosylation sites was expressed in the yeast system.

Matrix-assisted laser desorption/ionization mass spectrometry compatible beta-elimination of O-linked oligosaccharides

A new beta-elimination procedure has been introduced to cleave O-linked oligosaccharides from low- to sub-microgram amounts of glycoproteins prior to analysis by mass spectrometry. Borane-ammonia complex in aqueous ammonia is used as a cleaving solution alternative to the sodium borohydride/sodium hydroxide medium conventionally used in beta-elimination. The procedure results in minimum sample purification, leading to minimal sample loss and consequently an overall enhancement in sensitivity. It was applied successfully in the analysis of bovine fetuin and submaxillary mucin, as well as to a complex bile-salt-stimulated lipase glycoprotein isolated from human milk.

The nematode Caenorhabditis elegans synthesizes unusual O-linked glycans: identification of glucose-substituted mucin-type O-glycans and short chondroitin-like oligosaccharides

The free-living nematode Caenorhabditis elegans is a relevant model for studies on the role of glycoconjugates during development of multicellular organisms. Several genes coding for glycosyltransferases involved in the synthesis of N- and O-linked glycans have already been isolated, but, apart from repetitive dimers of glycosaminoglycans, no detailed structure of either type of component has been published so far. This study aimed to establish the structures of the major O-glycans synthesized by C. elegans to give an insight into the endogenous glycosyltransferase activities expressed in this organism. By the use of NMR and MS, we have resolved the sequence of seven of these components that present very unusual features. Most of them were characterized by the type-1 core substituted on Gal and/or GalNAc by (beta1-4)Glc and (beta1-6)Glc residues. Another compound exhibited the GalNAc(beta1-4)N-acetylglucosaminitol sequence in the terminal position, to which was attached a tetramer of beta-Gal substituted by both Fuc and 2-O-methyl-fucose residues. Our experimental procedure led also to the isolation of glycosaminoglycan-like components and oligomannosyl-type N-glycans. In particular, the data confirmed that C. elegans synthesizes the ubiquitous linker sequence GlcA(beta1-3)Gal(beta1-3)Gal(beta1-4)Xyl.

Matrix glycosaminoglycans in the growth phase of fibroblasts: more of the story in wound healing

BACKGROUND

Understanding wound healing and ways to accelerate the healing process includes understanding the factors that influence the synthesis of granulation tissue, which fills the wound before epithelialization. An important phase of early wound healing involves secretion of glycosaminoglycans (GAGs) by fibroblasts which form a hydrophilic matrix suitable for remodeling during healing. The complexity of GAG structure and function in the extracellular matrix (ECM) remains poorly studied in wound healing. There is no established model for cutaneous wound healing due to variations in donor age, anatomic site, or stage of organ development. Rat embryo fibroblasts (REF) developed as a model to study malignant changes in fibroblasts were used as a model for fibroblasts in early wound healing because they lack the confounding variations based on age, site, and stage present in other fibroblasts used to study early wound healing. The purpose of this study was to identify and characterize the sulfated GAGs synthesized by REF-D.

MATERIALS AND METHODS

Rat embryo fibroblasts (REF-D) were cultured in serum-based medium and radiolabeled during their growth phase with (35)S to identify the GAG chains usually associated with proteoglycans (PGs). The sites of attachment (ECM-rich) were collected with detergent in sodium acetate buffer, pH 5.8, in the presence of protease inhibitors. Sulfated molecules were collected by ion-exchange chromatography and then assayed for GAGs. Nitrous acid deamination was used to determine heparan sulfate GAGs, and chondroitinase was used for chondroitin/dermatan sulfate GAGs. The proportion of individual GAGs was expressed with respect to sulfated molecules isolated. In addition, RNA was isolated from subconfluent REF-D, and core proteins for proteoglycans (decorin, biglycan, syndecan-2, and perlecan) were assayed by reverse transcription polymerase chain reaction.

RESULTS

There were two major configurations of GAGs: free GAG chains (79.7% of sulfated molecules) and GAGs attached to the core protein of a proteoglycan (15.6%). The free GAG chains were composed of chondroitin sulfate (79.1% +/- 3.5) and heparan sulfate (28.7% +/- 2.1). In the smaller group of PGs, both heparan sulfate (94.8% +/- 7.3) and chondroitin sulfate (88.9% +/- 3.2) chains were attached to a core protein. REF-D expressed mRNA for biglycan and decorin, which are chondroitin sulfate-containing PGs. In addition, REF-D expressed mRNA for syndecan-2 and perlecan, which are PGs that contain primarily heparan sulfate chains.

CONCLUSIONS

A majority of GAG chains synthesized by subconfluent REF-D are chondroitin sulfate. A smaller proportion of chondroitin sulfate chains associate with a core protein as part of a PG (e.g., biglycan, decorin, syndecan-2). Heparan sulfate chains are also present, with a small proportion associated with a core protein (e.g., the PGs syndecan-2, perlecan). The greater presence of free GAG chains forming weak interactions with surrounding molecules may assist fibroblasts that are moving and replicating during this phase. Therefore, REF-D are particularly well suited to study early wound healing by their expression of chondroitin sulfate chains and associated PGs without the influence of donor age, stage, or anatomic site.

High prevalence of 2-mono- and 2,6-di-substituted manol-terminating sequences among O-glycans released from brain glycopeptides by reductive alkaline hydrolysis

Di- to heptasaccharides isolated from total nondialyzable brain glycopeptides after release by alkaline borohydride treatment have been subjected to mass spectrometric and nuclear magnetic resonance spectroscopic analyses supplemented by TLC-MS analyses of derived neoglycolipids. A family of Manol-terminating oligosaccharides has been revealed which includes novel sequences with a 2, 6-disubstituted Manol: In contrast to the Manol-terminating HNK-1 antigen-positive chains described previously that occur as a minor population [Yuen, C.-T., Chai, W., Loveless, R.W., Lawson, A.M., Margolis, R.U. & Feizi, T. (1997) J. Biol. Chem. 272, 8924-8931], the above oligosaccharides are abundant. The ratio of these compounds to the classical N-acetylgalactosaminitol-terminating oligosaccharides is about 1 : 3. Thus, there appears to be in higher eukaryotes a major alternative pathway related to the yeast-type protein O-mannosylation, the enzymatic basis and functional importance of which now require investigation.

Biochemical and immunological analyses of the flagellin of Clostridium tyrobutyricum ATCC 25755

The monoclonal antibody 21E7-B12 (IgG3) can be used in a direct method of Clostridium tyrobutyricum detection based on an immunoenzymatic assay. Immunoelectron microscopy demonstrated that the 21E7-B12 antibody recognized the surface-exposed epitopes on the flagellar filaments of C. tyrobutyricum. After flagellar extraction, the purified flagellin showed an apparent molecular mass of 46 kDa with an isoelectric point of 3.6. Sugar staining, mild periodate oxidation and beta-elimination experiments showed that the flagellin was glycosylated and that the 21E7-B12 epitope was located in the sugar moiety. Amino acid composition showed that the flagellar filament protein contained a high percentage of serine and threonine, while proline was absent. The first 23 residues of the N-terminal were determined and sequence homology with other flagellins was found.

Isolation and characterization of ovarian cancer antigen CA 125 using a new monoclonal antibody (VK-8): identification as a mucin-type molecule

A new murine monoclonal antibody (MAb VK-8), detecting the CA 125 ovarian cancer antigen, was used to purify this antigen from OVCAR-3 ovarian cancer cells by affinity chromatography. The biochemical properties of the purified antigen are characteristic of a mucin-type glycoprotein: (1) the molecule is highly glycosylated (77% w/w), mainly with galactose, N-acetylglucosamine, and N-acetylgalactosamine, (2) the protein moiety is rich in serine, threonine and proline, (3) many of the serine and threonine residues are glycosylated, (4) the glycan chains are almost entirely O-linked, with core 2 [Galbeta1 --> 3(GlcNAcbeta1 --> 6)GalNAc] structures predominating and (5) these chains carry fucosylated Type 2 (Le(y) and Le(x) and H type 2) blood group structures. The antigen exhibited a very high m.w. (> 10(3) kDa) in aqueous buffer as well as in urea, but was degraded by proteolytic enzymes to smaller fragments that no longer reacted with the antibody. Although this result, and other immunochemical data, indicate that OC125, the original MAb to CA125, and VK-8 antibodies detect epitopes on the protein portion of the molecule, the involvement of carbohydrate cannot be ruled out. Further insight into the structure and function of the CA125 antigen will come from cloning the gene coding for the peptide backbone, and from more detailed carbohydrate structural analysis.

Comparison of O-linked carbohydrate chains in MUC-1 mucin from normal breast epithelial cell lines and breast carcinoma cell lines. Demonstration of simpler and fewer glycan chains in tumor cells

MUC-1 mucin is considered to be aberrantly glycosylated in breast, ovary, and other carcinomas in comparison with mucin from corresponding normal tissues. In order to clarify these differences in glycosylation, we have compared the O-linked carbohydrate chains from MUC-1 immunoprecipitated from [3H]GlcN-labeled breast epithelial cell lines (MMSV1-1, MTSV1-7, and HB-2) derived from cells cultured from human milk, with three breast cancer cell lines (MCF-7, BT-20, and T47D). Analysis by high pH anion chromatography showed that the normal cell lines had a higher ratio of GlcN/GalN and more complex oligosaccharide profiles than the cancer cell lines. Structural analyses were carried out on the oligosaccharides from MTSV1-7 and T47D MUC-1, and the following structures were proposed. MUC-1 from T47D had rather a simple glycosylation pattern, with NeuAcalpha2-3Galbeta1-3GalNAc-ol, Galbeta1-3GalNAc-ol, and GalNAc-ol predominating; in contrast, MUC-1 from MTSV1-7 had more complex structures, including a number of disialo, core 2 species, i.e. NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-3]GalNAc- ol and NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-4GlcNAcbet a1-3Galbeta1-3]GalNAc-ol. Double-labeling experiments with [3H]GlcN and 14C-aminoacids and analysis of GalNAc or GalNAc-ol:protein ratios in MUC-1 showed that there was also a significant difference in the degree of glycosylation of the mucin between the two cell types. We conclude that MUC-1 from breast cancer cell lines has simpler, and fewer, carbohydrate chains than MUC-1 from normal breast epithelial cells, and that these differences, combined or separately, explain the differential tumor specificity of some MUC-1 antibodies and T cells.

The elimination of O-linked glycans from glycoproteins under non-reducing conditions

A simple procedure is described for the elimination of O-linked glycans from bovine submaxillary mucin under non-reducing conditions, using triethylamine in aqueous hydrazine. The glycans were isolated as the hydrazones, which were converted to the reducing glycans by exchange with acetone in neutral aqueous solution. The glycan alditols obtained after reduction corresponded to those obtained by the reductive beta-elimination of O-glycans.

Rat sublingual gland as a model to study glandular mucous cell secretion

To study the regulation of mucous cell secretion, we have developed an in vitro cell model consisting of enzymatically dispersed mucous acinar structures (cell aggregates) from rat sublingual glands. Histological and ultrastructural evidence demonstrates that the cell aggregates are highly enriched in mucous cells, retain the morphological and ultrastructural features observed in intact glands, and undergo transition to an extensive secretory state when stimulated by 10 microM carbachol. The secretory responsiveness of the cell aggregates was verified in pharmacological studies. Carbachol stimulated secretion in a dose-dependent manner with high affinity (concentration causing half-maximal response = 0.3 microM) and was completely inhibited by atropine. Secretion was also stimulated by vasoactive intestinal peptide and substance P but not by alpha- or beta-adrenergic agonists. Biochemical characterization of secretion during nonstimulated and carbachol-stimulated conditions (after preincubation in [3H]glucosamine) demonstrated that, in response to carbachol, cell aggregates synthesized and secreted mucins which were similar to mucin glycoproteins isolated from whole glands. Collectively, our results establish that the rat sublingual cell aggregate model is a viable and pharmacologically responsive cell system to study the regulation of mucous cell secretion.

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

Enzyme degradation, high performance liquid chromatography and liquid secondary ion mass spectrometry in the analysis of glycoproteins

Analysis of small amounts of glycoproteins by high performance liquid chromatography (HPLC) and liquid secondary ion mass spectrometry (LSIMS) together with enzyme digestion has been investigated using fetuin as a model. Preliminary data indicates that 71% of the expected peptides were detected by LSIMS analysis of 200 pmol total digest. HPLC profiles of peptides and glycopeptides were obtained from 2 nmol of digest using a reversed phase (C18) column eluted in a solvent system containing TFA, water and acetonitrile. This has provided glycopeptides for subsequent oligosaccharide analysis. Strategies are reviewed for the chromatographic characterization of oligosaccharides following their release from glycopeptides by chemical and enzymatic procedures.

Colorimetric determination of N-acetylhexosamine-terminating O-glycosidically linked saccharides in mucins and glycoproteins

A sensitive colorimetric assay for detecting mucins and glycoproteins rich in O-glycosidically linked saccharides is reported. The method combines the susceptibility of N-acetylgalactosamine terminating O-glycosidically linked saccharides to beta-elimination with the Morgan-Elson reaction for N-acetylhexosamines with free reducing ends. All mucin and mucin-type glycoproteins but none of the serum-type glycoproteins tested resulted in characteristic color production. All mucins tested gave linear responses in the range 5 to 200 micrograms and the assay was also adapted to the microscale involving the use of 96-well microtiter plates. The microassay in which the volumes of samples and reagents are scaled down 2.5-fold was particularly useful in monitoring of mucins, in the presence of other glycoconjugates, in large numbers of samples obtained during fractionation procedures. Cesium chloride, cesium bromide, potassium thiocyanate, and various detergents do not interfere with the colorimetric determination. Guanidine hydrochloride, cesium trifluoroacetate, and beta-mercaptoethanol decreased color by 30 to 45%; however, the interference was not serious to prevent the use of the method for detection of mucins in their presence. The use of the method for the specific detection of mucin during fractionation by gel filtration and density gradient centrifugation of cystic fibrosis sputum samples is demonstrated.

Sialyltransferases of developing rat brain

The activity of four different sialyltransferases acting on N- or O-linked chains of glycoproteins was studied in brains of 19 days-old embryos, 1-day-old newborns and adult rats. By using asialofetuin, fetuin and N-acetyllactosamine as acceptors, it has been possible to measure independently the following enzyme activities: CMP-NeuAc:Gal beta 1-3GalNAc alpha(2-3)-sialyltransferase (EC 2.4.99.4), CMP-NeuAc:Gal beta 1-4GlcNAc alpha(2-3)-sialyltransferase (EC 2.4.99.6), CMP-NeuAc:Gal beta 1-4GlcNAc alpha(2-6)-sialyltransferase (EC 2.4.99.1) and CMP-NeuAc:NeuAc alpha 2-3Gal beta 1-3GalNAc alpha(2-6)-sialyltransferase (EC 2.4.99.7). The specific activity of the first three enzymes which act on asialylated acceptors showed a 2.6-fold decrease in a parallel manner after ontogenic development, while the activity of NeuAc alpha 2-3Gal beta 1-3GalNAc alpha(2-6)-sialyltransferase was four times lower in adult than in embryonic brain, showing a stronger dependence on ontogenic development. Despite the higher level of sialyltransferases able to act on glycoproteins, in fetal brain these glycoproteins do not contain a higher amount of sialic acid.

Human yolk-sac tumor antigen 2G10: biochemical characterization and significance as a serum antigen

The biochemical characterization of human yolk-sac tumor (YST) antigen 2G10, detected by monoclonal antibody (MAb) M912-2G10, was studied. Previous results indicated that glycolipids having a non-reducing terminal N-acetyllactosamine structure were the epitope of 2G10 on human erythrocytes. In this study, the glycoprotein nature of 2G10 on the infantile embryonal carcinoma line, MTE, was investigated. 2G10 activity, measured by a new enzyme-linked immunosorbent assay (2G10-ELISA), was recovered in residual fractions of MTE from which glycolipids were removed. Chromatographically, 3H-galactose-labelled 2G10 on MTE had a molecular weight (mw) of about 580 kDa, which decreased after pronase or alkaline-borohydride treatment. Our results indicate the glycoprotein nature of 2G10 on MTE. Furthermore, 2G10, both on erythrocytes and on MTE, was sensitive to galactosidase but not to neuraminidase and fucosidase, suggesting that terminal galactose is involved in the antigenic structure. It was also found by 2G10-ELISA that 2G10 sheds from tumor cells. Shedding occurs in nude mice transplanted with MTE as well as in patients with germ-cell tumors (GCTs). The serum level of 2G10 in non-tumor patients was low, but high levels were detected in patients with YSTs and with GCTs having YST components. Immunohistochemically, the presence of 2G10-positive YST components was shown in patients who had high serum levels of 2G10. Sera from other urogenital and childhood solid tumors did not have elevated 2G10. The mw of shed 2G10 was lower than that of 2G10 on the cell surfaces. Our results clearly indicate the usefulness of serum 2G10 as a tumor marker for GCTs having YST components.

Identification of a human monocyte antigen (Mo3e) associated with cellular activation and lymphokine responsiveness

A murine monoclonal IgM antibody recognizes an antigen (Mo3e) found on the surface of human peripheral blood monocytes stimulated with phorbol 12-myristate 13-acetate (PMA), lipopolysaccharide and muramyl dipeptide and blocks the monocyte response to migration inhibitory factor (MIF). We utilized Western blot and immunoprecipitation analyses of whole cell lysates to investigate the biochemical nature of this monocyte antigen. Two distinct bands (75 kDa and 50 kDa) were detected by anti-Mo3e after monocyte lysates were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transblotted onto nitrocellulose paper. Stimulation of monocytes with PMA resulted in a marked increase in the amount of the 50-kDa species. Immunoprecipitation of Mo3e from lysates of surface-iodinated cells demonstrated one broad band at 55-80 kDa which increased after PMA stimulation. The epitope identified by anti-Mo3e was resistant to 2-mercaptoethanol and heat treatment (100 degrees C/5 min) and was sensitive to trypsin or papain treatment. Two-dimensional SDS-PAGE analysis revealed that the 75-kDa species has an isoelectric point of 7.0 and the 50-kDa species is more acidic with an isoelectric point of 5.3. These results indicate that anti-Mo3e antibody defines unique monocyte proteins that may play a role as suggested by previous studies, in monocyte activation and responsiveness to MIF.

The effect of alkaline borohydride treatment on N-linked carbohydrates of glycoproteins

The effects of treatments of the glycoprotein ribonuclease-B, the proteins ribonuclease-A and myoglobin, and the glyco-amino acid GlcNAc beta(1-N)Asn with alkali, alkaline sodium borohydride, and aqueous sodium borohydride were systematically studied as a function of the concentration of the reagents, the temperature, and the length of the treatment. High-field 1H-NMR spectroscopy, chromatographic methods and amino-acid analysis were used to characterize products of the treatments of the various compounds. Our results indicate that mild alkaline borohydride treatment, as well as aqueous borohydride treatment alone, is capable of extensively degrading polypeptides and of partially releasing the N-linked glycans from ribonuclease-B. Initially, glycopeptides are produced, the peptide portion of which consists of several amino acids, which are further hydrolyzed to yield a mixture of glyco-asparagines and oligosaccharide-alditols in the ratio of approximately 4:1. Strong alkaline borohydride treatment of ribonuclease-B is capable of completely releasing the N-linked carbohydrates as oligosaccharide-alditols.

Parasite glycoconjugates: towards the exploitation of their structure

The parasitic protozoa express many unusual complex carbohydrates at the cell surface in the form of glycoproteins and glycophospholipids. In several cases, such molecules have been shown to be involved in parasite survival, infectivity and host-cell recognition. The carbohydrate chains of these glycoconjugates are often highly immunogenic, and can in some cases elicit protective immunity. The immunogenicity of some parasite glycans is a function of their unusual chemical structure as compared with mammalian glycans. This suggests differences in the glycosylation pathways between host and parasite due to their evolutionary distance. This article describes how a combination of biophysical and biochemical techniques can be used to determine the primary and three-dimensional structures of parasite carbohydrate and how this information might be exploited towards the development of new selective chemotherapeutic agents and synthetic vaccines.

Studies on the isolation and composition of human ocular mucin

A method for the isolation and purification of human ocular mucin from the brief saline extract of human ocular mucus is reported. Initial purification of ocular mucin was achieved by sequential chromatography of the saline-soluble mucus extract from an individual donor's mucus pool on columns of Sephadex G-50 and Sepharose CL-4B. A portion of such mucin isolate was subjected to quantitative analysis of the O-seryl (threonyl)-N-acetylgalactosaminyl linkage, characteristic of mucins, by alkaline beta-elimination and tritiated borohydride reduction. Following Bio-Gel P-2 filtration, the mucin isolate whose cleaved oligosaccharides contained tritiated galactosaminitol greater than 0.5 microCi mg-1, a value that represents at least 64% of that observed for bovine and ovine submaxillary reference mucins, was considered to be mucin-rich. These isolates were subjected to further purification on Sephacryl S-500 and DEAE-Trisacryl M column chromatographies. The purified mucin had a minimum molecular weight of 120 kDa. It consisted of 25-30% protein and 54-55% carbohydrate. Its amino acid and carbohydrate compositions are characteristic of a mucin structure. The purity of the mucin was verified by SDS-gradient PAGE. Upon isoelectric focusing, polydispersity/microheterogeneity were exhibited in the pI range 5.0-6.6.

Analysis of IgG glycopeptides by alkaline borate gel filtration chromatography

A protocol for the characterization of IgG glycopeptides is described. Central to this scheme is the novel application of an alkaline borate buffer to gel filtration chromatography. The use of this buffer significantly enhances the resolution of glycopeptides. Furthermore, it results in the separation of a unique size class of glycopeptides derived from IgG secreted by murine hybridomas. Although predominantly neutral, these glycopeptides differ both qualitatively and quantitatively by lectin affinity chromatography from the other glycopeptides which are presumably derived from the Fc portion of IgG.

Structural studies on oncofetal carbohydrate antigens (Ca 19-9, Ca 50, and Ca 125) carried by O-linked sialyloligosaccharides on human amniotic mucins

Mucins were extracted from human amniotic fluid in the presence of 45% vol. phenol and separated from the bulk of smaller-sized glycoproteins by exclusion on Sephacryl S400. The mucin-fraction FW, which still contained a minute proportion of mannose, strongly expressed oncofetal antigens recognized by monoclonal antibodies C 50, NS 19-9, OC 125, Leu M1, 49 H 8, and 115 C 2. The structures of the respective mucin-linked saccharides responsible for Ca 50-, Ca 19-9-, and Lea-related antigenic activities were analyzed before or after reductive beta-elimination from sialylglycoproteins, and purification of the derived alditols by gel-permeation chromatography on Bio-Gel P-4 or high performance liquid chromatography. Two ubiquitous (FW2, FW3) and three novel oligosaccharide alditols (FW5) were characterized by f.a.b.- and e.i.-m.s., combined with methylation analysis and chromium trioxide oxidation. The OC 125 epitope on mucin-carried O-glycans was destroyed during reductive cleavage of the saccharides, indicating a conformational involvement of the reducing terminal residue and its mode of conjugation to the protein. Exoglycosidase treatment of the mucin-bound antigen revealed that the epitope structure of OC 125 includes terminal beta-D-galactosyl groups, and terminal sialyl groups that are almost inaccessible to Vibrio cholerae sialidase digestion.

A polysaccharide from Streptococcus sanguis 34 that inhibits coaggregation of S. sanguis 34 with Actinomyces viscosus T14V

Coaggregation between Actinomyces viscosus T14V and Streptococcus sanguis 34 depends on interaction of a lectin on A. viscosus T14V with a cell surface carbohydrate on S. sanguis 34. This carbohydrate was isolated, and its chemical makeup was established. The carbohydrate remained attached to S. sanguis 34 cells through extraction with Triton X-100 and treatment with pronase. It was cleaved from the cell residue by autoclaving and purified by differential centrifugation and column chromatography on DEAE-Sephacel and Sephadex G-75. The polysaccharide contained phosphate which was neither inorganic nor monoester. Treatment with NaOH-NaBH4, followed by Escherichia coli alkaline phosphatase, or with 48% HF at 4 degrees C, followed by NaBH4, yielded inorganic phosphate and oligosaccharide alditols. Therefore, the polysaccharide is composed of oligosaccharide units joined together by phosphodiester bridges. The structure and stereochemistry of the main oligosaccharide alditol was established previously (F. C. McIntire, C. A. Bush, S.-S. Wu, S.-C. Li, Y.-T. Li, M. McNeil, S. Tjoa, and P. V. Fennessey, Carbohydr. Res. 166:133-143). Permethylation analysis, 1H and 31P nuclear magnetic resonance studies on the whole polysaccharide revealed the position of the phosphodiester linkages. The polysaccharide is mainly a polymer of (6) GalNAc(alpha 1-3)Rha(beta 1-4)Glc(beta 1-6)Galf(beta 1-6)GalNAc(beta 1- 3)Gal(alpha 1)-OPO3. It reacted as a single antigen with antiserum to S. sanguis 34 cells and was a potent inhibitor of coaggregation between A. viscosus T14V and S. sanguis 34. Quantitative inhibition of precipitation assays with oligosaccharides, O-allyl N-acetylgalactosaminides, and simple sugars indicated that specific antibodies were directed to the GalNAc end of the hexasaccharide unit. In contrast, coaggregation was inhibited much more effectively by saccharides containing betaGalNAc. Thus, the specificity of the A. viscosus T14V lectin is strikingly different from that of antibodies directed against the S. sanguis 34 polysaccharide.

Expression of mouse embryonic epitope TEC-2 on human carcinoma-derived cell lines and characterization of its glycoprotein carriers

Monoclonal antibody TEC-02, raised against mouse embryonal carcinoma cells, has been shown to react with murine preimplantation embryos and with a very limited number of adult mouse tissues. The target epitope, TEC-2, is a carbohydrate carried in mouse embryonal carcinoma cells by large glycoprotein-bound glycan. We report here the expression of TEC-2 epitope on human carcinoma-derived cell lines, HeLa and HS, and the properties of its carbohydrate carriers. Immunolabeling of Nonidet P-40 lysates of HeLa cells separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that TEC-2 antigens are polydispersed glycoconjugates of high molecular weight (mostly above 100,000). TEC-2 antigens detected by the two-site sandwich assay, in which the antigen is immobilized and detected with the same antibody, had a slightly higher molecular weight than those detected by the solid-phase assay. This suggests heterogeneity in the number of TEC-2 epitopes per carrier molecule. When the cells were lysed by Triton X-114 and the detergent and aqueous phases were separated by warming and centrifugation, most of the TEC-2 antigenic activity was found in the aqueous phase. TEC-2 antigens isolated by indirect precipitation from [3H]galactose-labeled HeLa cells were degraded by extensive pronase digestion or mild alkaline treatment to glycopeptides or oligosaccharides of low molecular weight. Thus, TEC-2 epitope in human HeLa cells is carried by carbohydrates of only several monosaccharide units. TEC-02 antibody was also found to bind to Tamm-Horsfall glycoprotein isolated from human urine and its binding was enhanced by desialylation. Combined data indicate that TEC-02 antibody recognizes the GalNAc beta 1----4Gal beta 1----4 structure which may be carried on different types of molecule, according to the site of their synthesis.

Biochemistry and lectin binding properties of mammalian salivary mucous glycoproteins

The molecules responsible for the highly viscous properties of mucus are secretory glycoproteins referred to as mucins. Salivary mucins are characterized by a high sugar to protein ratio and are of a broad range of molecular weight from 7 x 10(4) to millions. With a few exceptions, they contain up to 30% of hexosamine (galactosamine and glucosamine), 8-33% of sialic acid, trace to 15% of galactose or fucose and little or no mannose. The size of carbohydrate side chains of these glycoproteins ranges from one to about fifteen units of sugar. These carbohydrate side chains are usually O-glycosidically linked through N-acetylgalactosamine to a peptidyl serine or threonine. In some instances, ester sulfate groups, mainly on N-acetylglucosamine, are also a structural feature. In many of these glycoproteins, the saccharide sequence is the same as that which determines the specificity of blood groups. Carbohydrate sequence analysis shows that salivary mucins exhibit considerable polydispersity, great diversity and remarkable structural flexibility not only among animal species but also within the same mucin molecule. Based on their lectin-binding ability, they can be used for purification of lectins, and lectins coupled to resin may be useful for the isolation of mucin-type glycoproteins. The epithelial mucous secretions modulate oral microbial flora; many secretory components serve as lectin-receptors for the attachment of microbes. The judicious use of lectins with widely differing binding characteristics has already been valuable in the in situ localization of salivary glycoproteins, in elucidating structural details, recording sugar density within a given tissue section, and defining host-parasite interactions. It is hoped that their use, together with monoclonal antibody (158) and tissue culture techniques (159, 160) will further clarify the roles of individual secretory mucous glycoproteins in health and disease.

High-performance liquid chromatographic analysis of galactosamine, glucosamine, glucosaminitol, and galactosaminitol

Both N-acetylgalactosamine and N-acetylglucosamine covalently link oligosaccharides to peptide in glycoproteins. In order to identify the N-acetylhexosamine involved in this linkage, the corresponding hexosaminitol generated by alkaline borohydride treatment must be determined. An HPLC method modified from the Waters PICO-TAG amino acid analysis procedure is described. Phenylisothiocarbamyl derivatives of galactosamine, glucosamine, glucosaminitol, galactosaminitol, and the internal standard, p-aminophenyl-beta-D-galactoside, are eluted from the Waters PICO-TAG column at 3.9, 4.3, 6.9, 8.1, and 10.1 min, respectively. The standard curves for the hexosamines and hexosaminitols are linear between 1 and 75 nmol. In addition to p-aminophenyl-beta-D-galactoside, several synthetic hexosamines and hexosaminitols can be employed as internal standard. These include 3-allosamine, 3-glucosamine, allosamine, 3-allosaminitol, mannosaminitol, and allosaminitol, which are eluted at 3.1, 3.4, 4.8, 6.4, 7.4, and 7.8 min, respectively. The analysis time is 15 min but can be shortened to 10 min if only hexosamines are to be analyzed and either 3-glucosamine or 3-allosamine is used as the internal standard. This rapid method is superior to previous methods for the analysis of hexosamines in glycoconjugates and hexosaminitols generated from glycoconjugates following alkaline borohydride treatment.

The structures of N- and O-glycosidic carbohydrate chains of a chondroitin sulfate proteoglycan isolated from the media of the human aorta

A large Mr chondroitin sulfate proteoglycan was extracted from the media of human aorta under dissociative conditions and purified by density-gradient centrifugation, ion-exchange chromatography, and gel filtration chromatography. Removal of a contaminating dermatan sulfate proteoglycan was accomplished by reduction, alkylation and rechromatography on the gel filtration column. After chondroitinase ABC treatment, the proteoglycan core was separated from a residual heparan sulfate proteoglycan by a third gel filtration chromatography step. As assessed by radioimmunoassay, the isolated proteoglycan core was free of link protein, but possessed epitopes that were recognized by antisera against the hyaluronic acid binding region of bovine cartilage proteoglycan as well as those that were weakly recognized by anti-keratan sulfate antisera. Following beta-elimination of the protein core, the liberated low Mr oligosaccharides were partially resolved by Sephadex G-50 chromatography, and their primary structure was determined by 500-MHz1H NMR spectroscopy in combination with compositional sugar analysis. The N-glycosidic carbohydrate chains, which were obtained as glycopeptides, were all biantennary glycans containing NeuAc and Fuc; microheterogeneity in the NeuAc----Gal linkage was detected in one of the branches. The N-glycosidic glycans have the following overall structure: (Formula: see text). The majority of the O-glycosidic carbohydrate chains bound to the protein core were found to be of the mucin type. They were obtained as glycopeptides and oligosaccharide alditols, and possessed the following structures: NeuAc alpha(2----3)Gal beta(1----3)GalNAc-ol, [NeuAc alpha(2----3)Gal beta(1----3)[NeuAc alpha(2----6)]GalNAc-ol, and NeuAc alpha-(2----3) Gal beta(1----3)[NeuAc alpha(2----3)Gal beta(1----4)GlcNAc beta(1----6)] GalNAc-ol. The remainder of the O-glycosidic carbohydrate chains bound to the isolated proteoglycan were the hexasaccharide link regions of the chondroitin sulfate chains that remained after chondroitinase ABC treatment of the native molecule. These latter glycans, which were obtained as oligosaccharide alditols, had the following structure (with GalNAc free of sulfate or containing sulfate bound at either C-4 or C-6): delta 4,5GlcUA beta(1----3)GalNAc beta(1----4)GlcUA beta(1----3)Gal beta(1----3)Gal beta(1----4)Xyl-ol.