The structure of carbohydrate unit B of porcine thyroglobulin

Roles of the structural units, glycotopes / mammalian N-glycans for Con A-glycan interactions, their codes, and their recognition factors

The binding property of Con A has been studied intensively and applied widely to glycoconjugates / glycobiology for over 80 years. However, its role and functional relationship of Con A with these mammalian structural units, glycotopes, N-glycan chains, as well as their polyvalent forms in N-glycoproteins involved in the Con A-glycan interactions have not been well defined and organized. In this study, the recognition factors involved in these interactions were analyzed by our well developed method- the enzyme linked lectinosorbent (ELLSA) and inhibition assay. Based on all the data obtained, it is concluded that Con A, as previously reported, has a relatively broad and wide recognition ability of the Manα1 → and Glcα1 → related glycans. It reacted not only strongly with yeast mannan and glycogens, but also bound well with a large number of mammalian N-glycans, including the N-glycans of rat sublingual gp (RSL), human Tamm-Horsfall glycoprotein (THGP), thyroglobulin and lactoferrin. The recognition specificity of Con A towards ligands, expressed by Molar Relative Potency (Molar R.P.), in a decreasing order is as follows: α1 → 3, α1 → 6 Mannopentaose (M5) and Biantennary N-linked core pentasaccharide (MDi) ≥ α1 → 3, α1 → 6 Mannotriose (M3) > Manα1 → 3Man (α1 → 3Mannobiose), Manα1 → 2Man (α1 → 2Mannobiose), Manα1 → 6Man (α1 → 6Mannobiose), Manα1 → 4Man (α1 → 4Mannobiose) > GlcNAcβ1 → 2Man (β1 → 2 N-Acetyl glucosamine-mannose) > Manα1 → /Glcα1 → > Man > Glc, while Gal / GalNAc were inactive. Furthermore, the Man related code system, in this study, is proposed to express by both numbers of Man and GlcNAcβ1 → branches (M3 to M9 / MMono to Penta etc.) and a table of three Manα1 → and Glcα1 → related biomasses of six recognition factors involved in the Con A-glycan interactions has also been demonstrated. These themes should be one of the most valuable advances since 1980s.

Capitalizing glycomic changes for improved biomarker-based cancer diagnostics

Cancer serum biomarkers are valuable or even indispensable for cancer diagnostics and/or monitoring and, currently, many cancer serum markers are routinely used in the clinic. Most of those markers are glycoproteins, carrying cancer-specific glycan structures that can provide extra-information for cancer monitoring. Nonetheless, in the majority of cases, this differential feature is not exploited and the corresponding analytical assays detect only the protein amount, disregarding the analysis of the aberrant glycoform. Two exceptions to this trend are the biomarkers α-fetoprotein (AFP) and cancer antigen 19-9 (CA19-9), which are clinically monitored for their cancer-related glycan changes, and only the AFP assay includes quantification of both the protein amount and the altered glycoform. This narrative review demonstrates, through several examples, the advantages of the combined quantification of protein cancer biomarkers and the respective glycoform analysis, which enable to yield the maximum information and overcome the weaknesses of each individual analysis. This strategy allows to achieve higher sensitivity and specificity in the detection of cancer, enhancing the diagnostic power of biomarker-based cancer detection tests.

Analysis of 2-aminopyridine labeled glycans by dual-mode online solid phase extraction for hydrophilic interaction and reversed-phase liquid chromatography

Quantitative analysis of glycans released from glycoproteins using high-performance liquid chromatography (HPLC) requires fluorescent tag labeling to enhance sensitivity and selectivity. However, the methods required to remove large amounts of excess labeling reagents from the reaction mixture are time-consuming. Furthermore, these methods, including solvent extraction and solid phase extraction (SPE), often impair quantitative analysis. Here, we developed an online sample cleanup procedure for HPLC analysis of 2-aminopyridine (AP)-labeled glycans using a six-port/two-way valve and two small columns: one packed with a strong cation exchange resin (SCX) and the other comprising ODS silica gel. AP-labeled glycans delivered from an injection port were separated from excess AP by passing through an SCX column (4.6 mm i.d., 1 cm long) regulated to 40°C. The AP-labeled glycans were trapped on an ODS column (4.6 mm i.d., 1 cm long) to further separate them from inorganic contaminants. By changing the valve position after 2 min to connect the ODS column to an analysis column, AP-labeled glycans trapped in the ODS column were eluted with an acetonitrile-containing eluent followed by hydrophilic interaction liquid chromatography (HILIC) separation on an amide column or reversed-phase mode separation on a C30 column. This method was successfully used to analyze N-linked glycans released from several glycoprotein samples.

Induction of specific adaptive immune responses by immunization with newly designed artificial glycosphingolipids

We previously found that artificial glycosphingolipids (artGSLs) containing very-long-chain fatty acids behave as strong immunogens in mice and promote the production of antibodies recognizing the oligosaccharide portion of artGSLs as the epitope. Here, we report that the oligosaccharide structure of artGSLs influences these immunogenic properties. We evaluated the antibody-inducing activity of artGSLs with different oligosaccharide structures in mice and found strong IgG-inducing activity only with an artGSL containing a core-fucosylated tetraoligosaccharide (Manβ1,4GlcNAcβ1,4[Fucα1,6]GlcNAc). To characterize the immunogenic properties of this artGSL, we analyzed various derivatives and found that the non-reducing terminal mannose structure was critical for the antibody-inducing activity. These artGSLs also exhibited IgG-inducing activity dependent on co-administration of lipid A adjuvant, but no cytokine-inducing activity similar to α-galactosylceramide was detected. Furthermore, repetitive immunization with the artGSL promoted the production of antibodies against a core-fucosylated α-fetoprotein isoform (AFP-L3) known as a hepatocellular carcinoma–specific antigen. These results indicate that the newly designed artGSLs specifically induce adaptive immune responses and promote antibody production by B cells, which can be utilized to develop anti-glycoconjugate antibodies and cancer vaccines targeting tumor-associated carbohydrate antigens.

The role of thyroglobulin in thyroid hormonogenesis

In humans, the thyroid hormones T₃ and T₄ are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T₄ and T₃ at distinct sites. T₄ formation involves oxidative coupling between two DIT side chains, and de novo T₃ formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T₃ formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

Large-scale quantitative isolation of pure protein N-linked glycans

Glycoproteins are biologically active proteins of which the attached glycans contribute to their biological functionality. Limited data is available on the functional properties of these N-glycans in isolation, without the protein core. Glycan release, typically performed with the PNGase F enzyme, is achieved on denatured proteins in the presence of detergents which are notoriously difficult to be completely removed. In this work we compared two methods aiming at recovering N-glycans in a high yield and at high purity from a PNGase F glycoprotein digest of bovine lactoferrin. Detergents were removed from the digest by two separate approaches. In the first approach, protein and glycans were precipitated with acetone and the detergent containing supernatant was discarded. In the second approach, detergent was removed by adsorption onto a polystyrene resin. Following detergent removal, the glycans were further purified by a sequence of solid phase extraction (SPE) steps. Both approaches for detergent removal yielded a final glycan purity above 85%. Recovery of the glycans from lactoferrin was, however, much lower when utilizing acetone precipitation versus the polystyrene resin; 52% versus 85% respectively. A more detailed analysis of the acetone precipitation step revealed a loss of shorter oligomannose structures specifically. A loss of glycans of lesser complexity (oligomannose and biantennary structures) was also observed for other glycoproteins (RNase B, porcine thyroglobulin, human lactoferrin). These results indicate that acetone precipitation, a commonly used step for small-scale glycan purification, is not suitable for all target glycoproteins. The polystyrene resin detergent removal step conserved the full N-glycan profile and could be applied to all mammalian glycoproteins tested. Using this optimized protocol, large-scale quantitative isolation of N-glycan structures was achieved with sufficient purity for functional studies.

Mosquito-larvicidal BinA toxin displays affinity for glycoconjugates: Proposal for BinA mediated cytotoxicity

Lysinibacillus sphaericus parasporal BinAB toxin displays mosquito larvicidal activity against Culex and Anopheles, but several Aedes species are refractory. Recently reported crystal structure of BinAB revealed the presence of N-terminal lectin-like domain in BinA. Hemagglutination and hemolytic activities were not observed for BinA in the present studies. We attempted to characterize carbohydrate specificity of BinA by high-throughput approaches using extrinsic fluorescence and thermofluor shift assay. A total of 34 saccharides (mono-, di- and polysaccharides, and glycoproteins) were used for initial high-throughput screening. The promising glycans were identified based on significant change in the fluorescence intensity. Surface plasmon resonance revealed differential binding of BinA with glycoproteins (fetuin, asialofetuin and thyroglobulin) and affinity for simple sugars, l-fucose and l-arabinose. In the limited carbohydrate competition assay, arabinose, fucose and fetuin inhibited BinA toxicity towards Culex larvae. This study for the first time provides direct evidence that BinA is competent to bind diverse and structurally different glycosylated proteins. This activity may be linked to its intracellular cytotoxicity, as protein N-glycosylation is thought to be critical for development and survival of insect larvae. The glycoproteins do not form stable complexes with BinA, however, as observed in the pull-down assay using affinity immobilized BinA and in native-PAGE analysis. As BinA displays only mild affinity with receptor polypeptide, we hypothesize that toxin-receptor specificity of BinA in Culex may be mediated by dual interaction of BinA with glycan core of GPI anchor and receptor polypeptide. The study shall be useful for refining strategies for improving larvicidal activity and for broadening target specificity of BinAB toxin.

Comparing MALDI-MS, RP-LC-MALDI-MS and RP-LC-ESI-MS glycomic profiles of permethylated N-glycans derived from model glycoproteins and human blood serum

The glycomic profiling of purified glycoproteins and biological specimen is routinely achieved through different analytical methods, but mainly through MS and LC-MS. The enhanced ionization efficiency and improved tandem MS interpretation of permethylated glycans have prompted the popularity of this approach. This study focuses on comparing the glycomic profiling of permethylated N-glycans derived from model glycoproteins and human blood serum using MALDI-MS as well as RP-LC-MALDI-MS and RP-LC-ESI-MS. In the case of model glycoproteins, the glycomic profiles acquired using the three methods were very comparable. However, this was not completely true in the case of glycans derived from blood serum. RP-LC-ESI-MS analysis of reduced and permethylated N-glycans derived from 250 nl of blood serum allowed the confident detection of 73 glycans (the structures of which were confirmed by mass accuracy and tandem MS), while 53 and 43 structures were identified in the case of RP-LC-MALDI-MS and MALDI-MS analyses of the same sample, respectively. RP-LC-ESI-MS analysis facilitates automated and sensitive tandem MS acquisitions. The glycan structures that were detected only in the RP-LC-ESI-MS analysis were glycans existing at low abundances. This is suggesting the higher detection sensitivity of RP-LC-ESI-MS analysis, originating from both reduced competitive ionization and saturation of detectors, facilitated by the chromatographic separation. The latter also permitted the separation of several structural isomers; however, isomeric separations pertaining to linkages were not detected.

Recognition roles of the carbohydrate glycotopes of human and bovine lactoferrins in lectin-N-glycan interactions

BACKGROUND

Lactoferrin is an iron-binding protein belonging to the transferrin family. In addition to iron homeostasis, lactoferrin is also thought to have anti-microbial, anti-inflammatory, and anticancer activities. Previous studies showed that all lactoferrins are glycosylated in the human body, but the recognition roles of their carbohydrate glycotopes have not been well addressed.

METHODS

The roles of human and bovine lactoferrins involved in lectin-N-glycan recognition processes were analyzed by enzyme-linked lectinosorbent assay with a panel of applied and microbial lectins.

RESULTS AND CONCLUSIONS

Both native and asialo human/bovine lactoferrins reacted strongly with four Man-specific lectins - Concanavalia ensiformis agglutinin, Morniga M, Pisum sativum agglutinin, and Lens culinaris lectin. They also reacted well with PA-IIL, a LFuc>Man-specific lectin isolated from Pseudomonas aeruginosa. Both human and bovine lactoferrins also recognized a sialic acid specific lectin-Sambucus nigra agglutinin, but not their asialo products. Both native and asialo bovine lactoferrins, but not the human ones, exhibited strong binding with a GalNAc>Gal-specific lectin-Wisteria floribunda agglutinin. Human native lactoferrins and its asialo products bound well with four Gal>GalNAc-specific type-2 ribosome inactivating protein family lectins-ricin, abrin-a, Ricinus communis agglutinin 1, and Abrus precatorius agglutinin (APA), while the bovine ones reacted only with APA.

GENERAL SIGNIFICANCE

This study provides essential knowledge regarding the different roles of bioactive sites of lactoferrins in lectin-N-glycan recognition processes.

In situ fabrication of ionic polyacrylamide-based preconcentrator on a simple poly(methyl methacrylate) microfluidic chip for capillary electrophoresis of anionic compounds

A simple and efficient method was developed for fabrication of an anionic sample preconcentrator on a channel of a commercial poly(methyl methacrylate) (PMMA)-made microchip using no photolithography or etching technique. The originality of our preconcentrator is based on simple photochemical copolymerization of monomers using the following procedure: All channels of the PMMA-made microchip were filled with gel solution comprising acrylamide, N,N'-methylene-bisacrylamide, and 2-acrylamide-2-methylpropanesulfonic acid with riboflavin as a photocatalytic initiator. In situ polymerization near the cross of the sample outlet channel was performed by irradiation with an argon ion laser beam, which is also used as the light source for fluorometric detection. The electrokinetic property and electric repulsion between sample components and anionic groups on the polyacrylamide gel layer produce, trap, and concentrate anions within a few minutes at the interface of the cathodic side of the gel layer. This method displays concentration factors as high as 10 (5). The availability of ionic preconcentrator was demonstrated by applying sensitive analysis of oligosaccharides labeled with 8-aminopyrene-1,3,6-trisulfonate and some glycoproteins labeled with fluorescein isothiocyanate under various buffer systems.

VIPL has sugar-binding activity specific for high-mannose-type N-glycans, and glucosylation of the α1,2 mannotriosyl branch blocks its binding

VIP36-like protein (VIPL) was identified as an endoplasmic reticulum (ER) resident protein with homology to VIP36, a cargo receptor involved in the transport of glycoproteins within cells. Although VIPL is structurally similar to VIP36, VIPL is thought not to be a lectin, because its sugar-binding activity has not been detected in several experiments. Here, recombinant soluble VIPL proteins (sVIPL) were expressed in Escherichia coli, biotinylated with biotin ligase and oligomerized with R-phycoerythrin (PE)-labeled streptavidin (SA). As measured with flow cytometry, PE-labeled sVIPL-SA bound to deoxymannojirimycin (DMJ)- or kifunensine (KIF)- but not to swainsonine (SW)-treated HeLaS3 cells in the presence of calcium. A surface plasmon resonance analysis showed that the avidity of sVIPL was enhanced after it formed a complex with SA. The binding of PE-labeled sVIPL-SA was abrogated by endo beta-N-acetylglucosaminidase H treatment of the DMJ- or KIF-treated cells. Competition with several high-mannose-type N-glycans inhibited VIPL binding, and indicated that VIPL recognizes the Manalpha1-2Manalpha1-2Man sequence. Glucosylation of the outer mannose residue of this portion decreased the binding. Although the biochemical characteristics of VIPL are similar to those of VIP36, the sugar-binding activity of VIPL was stronger at neutral pH, corresponding to the pH in the lumen of the ER, than under acidic conditions.

Presence of beta-linked GalNAc residues on N-glycans of human thyroglobulin

Hepatic asialoglycoprotein receptor, which may mediate the clearance of circulating thyroglobulin, is known to have a high affinity for GalNAc. Recently, the receptor has been reported to be present also in the thyroid, implicating interaction with thyroglobulin. Here, mammalian thyroglobulins were analyzed for GalNAc termini by Western blotting with GalNAc-recognizing lectins labeled with peroxidase or (125)I. Wistaria floribunda lectin was found to bind human thyroglobulin and, to some extent, bovine, but not porcine thyroglobulin. After desialylation, the lectin bound all of the thyroglobulins tested. The binding was inhibited by competitive inhibitor GalNAc. Peptide N-glycanase treatment of human desialylated thyroglobulin resulted in the complete loss of reactivity with W. floribunda lectin, indicating that the binding sites are exclusively on N-glycans. The binding sites on human desialylated thyroglobulin were partly sensitive to beta-galactosidase, and the remainder was essentially sensitive to beta-N-acetylhexosaminidase. On the other hand, the binding sites of bovine and porcine desialylated thyroglobulins were totally sensitive to beta-galactosidase. Thus the lectin binds beta-Gal termini, as well as beta-GalNAc. GalNAc-specific Dolichos biflorus lectin also bound human thyroglobulin weakly. In contrast to W. floribunda lectin, desialylation diminished binding, suggesting that these two lectins recognize different GalNAc-terminated structures. Again, the binding was inhibited by GalNAc and by treatment with peptide N-glycanase. These results strongly indicate the presence of distinct GalNAc termini of N-glycans on human thyroglobulin.

Novel Carbohydrate-binding Activity of Pancreatic Trypsins to N-Linked Glycans of Glycoproteins

How glycosylation affects the reactivity of proteins to trypsin is not well understood. Bovine and porcine pancreatic trypsins were discovered to bind to alpha-Man, Neu5Acalpha2,6Galbeta1,4Glc, and alpha-galactose sequences by binding studies with biotinylated sugar-polymers. Quantitative kinetic studies supported that phenylmethylsulfonyl fluoride (PMSF)-treated trypsin binds to glycolipid analogues possessing alpha-Man or alpha-NeuAc but not to those possessing beta-galactose or beta-GlcNAc residue. Enzyme-linked immunosorbent assay (ELISA) showed that trypsin binds to six kinds of biotinylated glycoproteins possessing high mannose-type and complex-type N-glycans but not to bovine submaxillary mucin, which possesses only O-glycans. Further, the binding of trypsin to glycoproteins was differentially changed by treatments with sequential exoglycosidases, endoglycosidase H, or N-glycosidase F. Quantitative kinetic studies indicated that PMSF-treated trypsin binds with bovine thyroglobulin with the affinity constant of 10(10) m(-1), which was the highest among the glycoproteins examined, and that alpha-galactosidase treatment decreased it to 10(5) m(-1). PMSF-treated trypsin bound to other glycoproteins, including ovomucoid, a trypsin inhibitor, with the affinity constants of 10(8)-10(5) mol(-1) and were markedly changed by glycosidase treatments in manners consistent with the sugar-binding specificities suggested by ELISA. Thus, the binding site for glycans was shown to be distinct from the catalytic site, allowing trypsin to function as an uncompetitive activator in the hydrolysis of a synthetic peptide substrate. Correspondingly the carbohydrate-binding activities of trypsin were unaffected by treatment with PMSF or soybean trypsin inhibitor. The results indicate the presence of an allosteric regulatory site on trypsin that sugar-specifically interacts with glycoproteins in addition to the proteolytic catalytic site.

Rapid and sensitive screening of N-glycans as 9-fluorenylmethyl derivatives by high-performance liquid chromatography: a method which can recover free oligosaccharides after analysis

There are a large number of labeling methods for asparagine-type oligosaccharides with fluorogenic and chromophoric reagents. We have to choose the most appropriate labeling method based on the purposes such as mass spectrometry, high-performance liquid chromatography and capillary electrophoresis. Asparagine-type glycans are released from core proteins as N-glycosylamine at the initial step of the releasing reaction when glycoamidase F is employed as the enzyme. The N-glycosylamine-type oligosaccharides thus released by the enzyme are subjected to hydrolysis or mutarotation to form free-form oligosaccharides. In the detailed studies on the enzyme reaction, we found a condition in which the released N-glycosylamine-type oligosaccharides were exclusively present at least during the course of enzyme reaction, and developed a method for in situ derivatization of the glycosylamine-type oligosaccharides with 9-fluorenylmethyl chloroformate (Fmoc-Cl). The Fmoc labeled sialo- and asialo- (or high-mannose and hybrid) oligosaccharides were successfully analyzed on an amine-bonded polymer column and amide-silica column, respectively. The present method showed approximately 5 times higher sensitivities than that using 2-aminobenzoic acid (2-AA). The separation profile was similar to that observed using 2-AA method as examined by the analyses of carbohydrate chains derived from several glycoproteins including complex-type, high-mannose type and hybrid type of N-linked oligosaccharides. The labeled oligosaccharides were stable at least for several months when stored at -20 degrees C. Furthermore, it should be emphasized that the Fmoc-derivatized oligosaccharides could be easily recovered as free reducing oligosaccharides simply by incubation with morpholine in dimethylformamide solution. We obtained a pure triantennary oligosaccharide with 3 sialic acid residues as a free reducing form from fetuin in good yield after isolation of the corresponding Fmoc oligosaccharide followed by removing reaction of the Fmoc group. The proposed method will be useful for preparation of free oligosaccharides as standard samples at pmol-nmol scale from commercially available glycoproteins.

Measurement of the carbohydrate-binding specificity of lectins by a multiplexed bead-based flow cytometric assay

Carbohydrate binding underlies many cell recognition events. Here, we describe a multiplexed glyco-bead array method for determining the carbohydrate-binding specificities of plant lectins using a bead-based flow cytometric analysis. N-glycans including high mannose, hybrid, and complex types and O-glycans from glycoproteins were immobilized on multiplexed beads, and the specificities of 13 kinds of sugar chains were monitored within 2 h in a single reaction. This strategy is easy, rapid, reproducible, and suitable for small samples and allows the reliable and simultaneous elucidation of sugar-binding properties under identical conditions.

Lectins from tropical sponges. Purification and characterization of lectins from genus Aplysina

Only a few animal phyla have been screened for the presence and distribution of lectins. Probably the most intensively studied group is the mollusk. In this investigation, 22 species from 12 families of tropical sponges collected in Los Roques National Park (Venezuela) were screened for the presence of lectins. Nine saline extracts exhibited strong hemagglutinating activity against pronase-treated hamster red blood cells; five of these reacted against rabbit red blood cells, four with trypsin-treated bovine red blood cells, and five with human red blood cells regardless of the blood group type. Extracts from the three species studied from genus Aplysina (archeri, lawnosa, and cauliformis) were highly reactive and panagglutinating against the panel of red blood cells tested. The lectins from A. archeri and A. lawnosa were purified to homogeneity by ammonium sulfate fractionation, affinity chromatography on p-aminobenzyl-beta-1-thiogalactopyranoside-agarose, and gel filtration chromatography. Both lectins exhibited a native molecular mass of 63 kDa and by SDS-polyacrylamide gel electrophoresis under reducing conditions have an apparent molecular mass of 16 kDa, thus suggesting they occur as homotetramers. The purified lectins contain 3-4 mol of divalent cation per molecule, which are essential for their biological activity. Hapten inhibition of hemagglutination was carried out to define the sugar binding specificity of the purified A. archeri lectin. The results indicate a preference of the lectin for nonreducing beta-linked d-Gal residues being the best inhibitors of red blood cells binding methyl-beta-d-Gal and thiodigalactoside (Gal beta 1-4-thiogalactopyranoside). The behavior of several glycans on immobilized lectin affinity chromatography confirmed and extended the specificity data obtained by hapten inhibition.

Selective organic precipitation/extraction of released N-glycans following large-scale enzymatic deglycosylation of glycoproteins

A major difficulty with isolating enzymatically or chemically released oligosaccharides from large-scale glycoprotein deglycosylation reactions is the time-consuming chromatography, desalting, and concentration steps required to prepare a glycan fraction of manageable proportions. To overcome these time and preparative chromatography equipment requirements, we have developed a rapid organic solvent precipitation/extraction procedure that allows sequential isolation of endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96)-released high-mannose and hybrid, peptide-N(4)-(N-acetyl-beta-glucosaminyl) Asn amidase (EC 3.5.1. 52)-released complex, and beta-eliminated O-linked glycans without the need for intermediate chromatography, desalting, or concentration steps. The method involves precipitation of protein and released glycans at -20 degrees C in 80% acetone and extraction of the glycans from the pellet with 60% aqueous methanol after each deglycosylation step. Three pools of essentially salt- and detergent-free oligosaccharides (high-mannose/hybrid, complex, and O-linked) can be isolated in a high yield in 4 days with this protocol, which has been extensively tested using bovine RNase B, human bile salt-stimulated lipase expressed in Pichia pastoris, hen ovalbumin, bovine fetuin, bovine thyroglobulin, and several invertase preparations from wild-type and mutant yeast strains.

Structural characterization of chemically derivatized oligosaccharides by nanoflow electrospray ionization mass spectrometry

Oligosaccharides released from several glycoproteins were derivatized with either 4-aminobenzoic acid 2-(diethylamino)ethyl ester (ABDEAE) (Yoshino, K.; et al. Anal. Chem. 1995, 67, 4028-4031) or 2-aminopyridine. The resulting derivatives were analyzed on a nanoflow electrospray ionization (ESI) quadrupole-inlet time-of-flight mass spectrometer using the low-energy collision-induced dissociation technique. In the MS/MS spectra, the oxonium (b or internal series) and y series ions, which are derived from the multiply charged precursor ions, were predominant and were used for the structural readout. Some oxonium ions that were observed in the low-mass region, but that were not found in the PSD analyses (Mo, W.; et al. Anal. Chem. 1998, 70, 4520-4526), rendered a more detailed structural insight. The oxonium ions at m/z 512.2, which are derived from the fucosylated oligosaccharides of immunoglobulin Y and thyroglobulin, were observed, suggesting that fucosylation had occurred proximal to the outer nonreducing terminus. In addition, the data herein show that structural elucidation can be routinely achieved at a low sample concentration. For the case of ABDEAE derivatives, this can be achieved at the 50 fmol/microL level and with the actual sample consumption at the attomole level using nanoflow ESI MS/MS.

Structural characterisation of N-linked glycan mixtures by precursor ion scanning and tandem mass spectrometric analysis

2-Aminoacridone (2-AMAC) labelled N-linked glycan pools were analysed directly by a hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-Tof) in the precursor ion scanning and tandem mass spectrometry (MS/MS) modes. The use of a precursor ion scanning strategy on this instrument provides a rapid and sensitive method of screening glycan mixtures, without prior separation by chromatographic methods. It allows facile and preliminary characterisation of glycans into different classes, for example, high-mannose or complex glycans. Preliminary sequencing information for each glycan is obtained in the initial precursor ion scanning mode, but further sequencing information of selected glycans can be obtained using the MS/MS mode. Copyright 1999 John Wiley & Sons, Ltd.

A comparative review of the structure and biosynthesis of thyroglobulin

Thyroglobulin, the major iodoglycoprotein of the thyroid (Mr 669 kDa) has a sedimentation coefficient of 19 S and an isoelectric point (pI) of 4.4-4.7. The protein has been isolated and purified from saline extracts of the gland of several animal species, by methods such as ammonium sulfate fractionation, DEAE-cellulose chromatography and Sepharose 4B/6B gel-filtration. DEAE-cellulose chromatography of thyroglobulin from many species, by linear gradient, yielded a complex elution pattern, while camel thyroglobulin showed only a major and minor peak. As an iodoprotein, the protein has 0.1-2.0% iodine. The amino acid and iodoamino acid composition of thyroglobulins, in general, is similar. However, a high thyroxine content (15 mol/mol protein) has been noted for buffalo species. Asparagine or aspartic acid has been reported as the major N-terminal amino acid for thyroglobulins of several animal species whereas glutamic acid is the sole N-terminal amino acid for buffalo thyroglobulin. As a glycoprotein, thyroglobulin contains 8-10% total carbohydrate with galactose, mannose, fucose, N-acetyl glucosamine and sialic acid residues. The carbohydrate in the protein is distributed as two distinct units, A and B. In addition, human thyroglobulin has carbohydrate unit C. The occurrence of sulfate and phosphate as Gal-3-SO4 and Man-6-PO4, respectively, has been reported in few species. The quaternary structure of native thyroglobulin is comprised of two equal sized subunits of 330 kDa. However, the protein appears to contain 4-8 non-identical units in few species. The synthesis of thyroid hormones occurs in the matrix of the protein and is regulated by pituitary thyrotropin. The role of tyrosine residues 5 and 130 in thyroxine synthesis has been well documented.

A chromatographic and mass spectrometric strategy for the analysis of oligosaccharides: determination of the glycan structures in porcine thyroglobulin

Oligosaccharides released from porcine thyroglobulin were first derivatised with 2-aminoacridone (2-AMAC) and analysed by capillary electrophoresis to determine the complexity of this glycan pool. The same glycan mixture was then subjected to either a sialidase digest or a sialidase and fucosidase digest prior to derivatisation with 2-AMAC and analysis by normal phase high pressure liquid chromatography (HPLC). Comparison of the three chromatographic profiles with known standards allowed an initial identification of the glycan structures. The 2-AMAC derivatised glycans were then collected from HPLC for matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) analysis and the molecular weights of predicted structures were confirmed. This study demonstrates that a two enzyme array and subsequent MALDI-TOF analysis can be used successfully to assign the major glycans present in a complex mixture.

High resolution and high sensitivity methods for oligosaccharide mapping and characterization by normal phase high performance liquid chromatography following derivatization with highly fluorescent anthranilic acid

Facile labeling of oligosaccharides (acidic and neutral) in a nonselective manner was achieved with highly fluorescent anthranilic acid (AA, 2-aminobenzoic acid) (more than twice the intensity of 2-aminobenzamide, AB) for specific detection at very high sensitivity. Quantitative labeling in acetate-borate buffered methanol (approximately pH 5.0) at 80 degreesC for 60 min resulted in negligible or no desialylation of the oligosaccharides. A high resolution high performance liquid chromatographic method was developed for quantitative oligosaccharide mapping on a polymeric-NH2bonded (Astec) column operating under normal phase and anion exchange (NP-HPAEC) conditions. For isolation of oligosaccharides from the map by simple evaporation, the chromatographic conditions developed use volatile acetic acid-triethylamine buffer (approximately pH 4.0) systems. The mapping and characterization technology was developed using well characterized standard glycoproteins. The fluorescent oligosaccharide maps were similar to the maps obtained by the high pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), except that the fluorescent maps contained more defined peaks. In the map, the oligosaccharides separated into groups based on charge, size, linkage, and overall structure in a manner similar to HPAEC-PAD with contribution of -COOH function from the label, anthranilic acid. However, selectivity of the column for sialic acid linkages was different. A second dimension normal phase HPLC (NP-HPLC) method was developed on an amide column (TSK Gel amide-80) for separation of the AA labeled neutral complex type and isomeric structures of high mannose type oligosaccharides. The oligosaccharides labeled with AA are compatible with biochemical and biophysical techniques, and use of matrix assisted laser desorption mass spectrometry for rapid determination of oligosaccharide mass map of glycoproteins is demonstrated. High resolution of NP-HPAEC and NP-HPLC methods combined with mass spectrometry (MALDI-TOF) can provide an effective technology for analyzing a wide repertoire of oligosaccharide structures and for determining the action of both transferases and glycosidases.

Carbohydrate analysis of porcine thyroglobulin isoforms with different iodine contents

To further validate the relationship between thyroid hormone formation and the carbohydrate structure of thyroglobulin (Tg), we reinvestigated the relationship between the iodine content and the asparagine-linked oligosaccharide structures of porcine Tg. Purified porcine Tg was further separated into isoforms (Tg-F1, -F2 and -F3) with a DEAE-cellulose ion-exchange chromatography column. The iodine residues, neutral sugar and sialic acid were analyzed for the separated Tg isoforms and their asparagine-linked oligosaccharide structures were analyzed. The asparagine-linked oligosaccharides were released from Tg-F1, -F2 and -F3 by hydrazinolysis and each oligosaccharide was labeled with p-aminobenzoic acid octyl ester (ABOE). The ABOE-labeled oligosaccharides from Tg-F1, -F2 and -F3 were analyzed for their relative content in oligosaccharides of each structure type by chemical methods and DEAE- and ConA high-performance liquid chromatography (HPLC) columns. As a result, it was revealed that the Tg fraction eluted at higher ionic strength from a DEAE-cellulose column is apt to contain more of each iodoamino acid, as well as total content of iodine, larger negative zeta-potential, conforming to sialic acid content in the Tg molecule and to a higher content of di-sialo-bi-antennary complex and to high mannose type oligosaccharides. These results support the conclusion that iodine organification of the Tg molecule is correlated with asparagine-linked oligosaccharide completion.

Purification and characterization of UDP-N-acetylglucosamine: alpha1,3-D-mannoside beta1,4-N-acetylglucosaminyltransferase (N-acetylglucosaminyltransferase-IV) from bovine small intestine

A new beta1,4-N-acetylglucosaminyltransferase (GnT) which involves in branch formation of Asn-linked complex-type sugar chains has been purified 224,000-fold from bovine small intestine. This enzyme requires divalent cations, such as Mn2+, and catalyzes the transfer of GlcNAc from UDP-GlcNAc to biantennary oligosaccharide and produces triantennary oligosaccharide with the beta1-4-linked GlcNAc residue on the Manalpha1-3 arm. The purified enzyme shows a single band of Mr 58,000 and behaves as a monomer. The substrate specificity demonstrated that the beta1-2-linked GlcNAc residue on the Manalpha1-3 arm (GnT-I product) is essential for the enzyme activity. beta1-4-Galactosylaion to this essential beta1-2-linked GlcNAc residue or N-acetylglucosaminylation to the beta-linked Man residue (bisecting GlcNAc, GnT-III product) blocks the enzyme action, while beta1-6-N-acetylglucosaminylation to the Manalpha1-6 arm (GnT-V product) increases the transfer. Based on these findings, we conclude that the purified enzyme is UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,4-N-acetylglucosaminyltransferase IV (GnT-IV), that has been a missing link on biosynthesis of complex-type sugar chains.

Intracellular protein transport to the thyrocyte plasma membrane: potential implications for thyroid physiology

We present a snapshot of developments in epithelial biology that may prove helpful in understanding cellular aspects of the machinery designed for the synthesis of thyroid hormones on the thyroglobulin precursor. The functional unit of the thyroid gland is the follicle, delimited by a monolayer of thyrocytes. Like the cells of most simple epithelia, thyrocytes exhibit specialization of the cell surface that confronts two different extracellular environments-apical and basolateral, which are separated by tight junctions. Specifically, the basolateral domain faces the interstitium/bloodstream, while the apical domain is in contact with the lumen that is the primary target for newly synthesized thyroglobulin secretion and also serves as a storage depot for previously secreted protein. Thyrocytes use their polarity in several important ways, such as for maintaining basolaterally located iodide uptake and T4 deiodination, as well apically located iodide efflux and iodination machinery. The mechanisms by which this organization is established, fall in large part under the more general cell biological problem of intracellular sorting and trafficking of different proteins en route to the cell surface. Nearly all exportable proteins begin their biological life after synthesis in an intracellular compartment known as the endoplasmic reticulum (ER), upon which different degrees of difficulty may be encountered during nascent polypeptide folding and initial export to the Golgi complex. In these initial stages, ER molecular chaperones can assist in monitoring protein folding and export while themselves remaining as resident proteins of the thyroid ER. After export from the ER, most subsequent sorting for protein delivery to apical or basolateral surfaces of thyrocytes occurs within another specialized intracellular compartment known as the trans-Golgi network. Targeting information encoded in secretory proteins and plasma membrane proteins can be exposed or buried at different stages along the export pathway, which is likely to account for sorting and specific delivery of different newly-synthesized proteins. Defects in either burying or exposing these structural signals, and consequent abnormalities in protein transport, may contribute to different thyroid pathologies.

Purification and carbohydrate-binding specificity of Agrocybe cylindracea lectin

A lectin was isolated from fruiting bodies of Agrocybe cylindracea by two ion-exchange chromatographies and gel filtration on Toyopearl HW55F. The lectin was homogeneous on polyacrylamide gel electrophoresis and its molecular mass was determined to be 30000 by gel filtration, and 15000 by sodium dodecylsulfate polyacrylamide gel electrophoresis, signifying a dimeric protein. Its carbohydrate-binding specificity was investigated both by sugar-hapten inhibition of hemagglutination and by enzyme-linked immunosorbent assay. The inhibition tests showed the affinity of the lectin to be weakly directed toward sialic acid and lactose, and the enhanced affinity toward trisaccharides containing the NeuAc alpha2,3Gal beta-structure. Importantly, the lectin strongly interacted with glycoconjugates containing NeuAc alpha2,3Gal beta1,3GlcNAc-/GalNAc sequences.

Endothelial cell GlcNAc beta 1-4GlcNAc epitopes for outer membrane protein A enhance traversal of Escherichia coli across the blood-brain barrier

Inadequate knowledge of pathogenesis and pathophysiology has contributed to the high mortality and morbidity associated with neonatal Escherichia coli meningitis. We have shown previously that outer membrane protein A (OmpA) contributes to E. coli K1 membrane invasion of brain microvascular endothelial cells. In this study we report that this OmpA+ K1 E. coli invasion of brain microvascular endothelial cells was inhibited by wheat germ agglutinin and chitooligomers prepared from the polymer of 1,4-linked GlcNAc, chitin. The specificity of the interaction between OmpA and GlcNAc beta 1-4GlcNAc epitopes was verified by the demonstration that chitotriose-bound OmpA and wheat germ agglutinin-bound brain microvascular endothelial cell membrane proteins inhibit E. coli K1 invasion. Of interest, OmpA+ E. coli invasion into systemic endothelial cells did not occur, but invasion similar to that of brain microvascular endothelial cells was observed when systemic cells were treated with alpha-fucosidase, suggesting that the GlcNAc beta 1-4GlcNAc moieties might be substituted with L-fucose on these cells. More importantly, the chitooligomers prevented entry of E. coli K1 into the cerebrospinal fluid of newborn rats with experimental hematogenous E. coli meningitis, suggesting that the GlcNAc beta 1-4GlcNAc epitope of brain microvascular endothelial cells indeed mediates the traversal of E. coli K1 across the blood-brain barrier. A novel strategy with the use of soluble receptor analog(s) may be feasible in the prevention of devastating neonatal E. coli meningitis.

Binding studies on the combining site of a GalNAc alpha 1-->-specific lectin with Thomsen-Friedenreich activity prepared from green marine algae Codium fragile subspecies tomentosoides

The combining site of a GalNAc alpha 1-->-specific lectin (CFT) with Thomsen-Friedenreich (T, Gal beta 1-->3-GalNAc alpha 1-->Ser/Thr) activity, purified from the subspecies tomentosoides of green marine algae Codium fragile was studied by quantitative precipitin and precipitin-inhibition assays. Of 27 glycoforms tested, Tn (GalNAc alpha 1-->Ser/Thr) glycoprotein from armadillo submandibular glands, and asialo porcine submandibular glycoprotein, which contains T, Tn and GalNAc alpha 1-->3Gal(A) sequences, completely precipitated the lectin added, and less than 1 microgram glycoprotein was required to precipitate 50% 4.7 micrograms lectin nitrogen. However, CFT precipitated negligibly with Pneumococcus type-XIV polysaccharide and asialo human alpha 1-acid glycoprotein, that contain exclusively the human blood-type-II precursor sequence (II, Gal beta 1-->4GlcNAc) at the nonreducing ends. Among the sugar inhibitors tested, the human blood A-active trisaccharide [Ah, GalNAc alpha 1-->3 (LFuc alpha 1-->2)Gal] was the best inhibitor; it was about twice as active as the T disaccharide. Oligosaccharides without GalNAc alpha 1--> as part of their sequences were inactive, indicating that the acetamido group at C2 of galactose is essential for binding and that GalNAc is the main contributor in the T sequence for binding. From the data provided, it is clear that the combining site of CFT requires an alpha-anomer of GalNAc and recognizes Ah, internal GalNAc alpha 1--> of T and Tn determinants of glycans, but not the blood group I/II (Gal beta 1-->3/4GlcNAc) sequences. Consequently, CFT is a useful reagent for detecting GalNAc alpha 1-->-containing glycoconjugates.

Selective reentry of recycling cell surface glycoproteins to the biosynthetic pathway in human hepatocarcinoma HepG2 cells

Return of cell surface glycoproteins to compartments of the secretory pathway has been examined in HepG2 cells comparing return to the trans-Golgi network (TGN), the trans/medial- and cis-Golgi. Transport to these sites was studied by example of the transferrin receptor (TfR) and the serine peptidase dipeptidylpeptidase IV (DPPIV) after labeling these proteins with the N-hydroxysulfosuccinimide ester of biotin on the cell surface. This experimental design allowed to distinguish between glycoproteins that return to these biosynthetic compartments from the cell surface and newly synthesized glycoproteins that pass these compartments during biosynthesis en route to the surface. Reentry to the TGN was measured in that surface glycoproteins were desialylated with neuraminidase and were monitored for resialylation during recycling. Return to the trans-Golgi was traced measuring the transfer of [3H]fucose residues to recycling surface proteins by fucosyltransferases. To study return to the cis-Golgi, surface proteins were metabolically labeled in the presence of the mannosidase I inhibitor deoxymannojirimycin (dMM). As a result surface proteins retained N-glycans of the oligomannosidic type. Return to the site of mannosidase I in the medial/cis-Golgi was measured monitoring conversion of these glycans to those of the complex type after washout of dMM. Our data demonstrate that DPPIV does return from the cell surface not only to the TGN, but also to the trans-Golgi thus linking the endocytic to the secretory pathway. In contrast, no reentry to sites of mannosidase I could be detected indicating that the early secretory pathway is not or is only at insignificant rates accessible to recycling DPPIV. In contrast to DPPIV, TfR was very efficiently sorted from endosomes to the cell surface and did not return to the TGN or to other biosynthetic compartments in detectable amounts, indicating that individual surface proteins are subject to different sorting mechanisms or sorting efficiencies during recycling.

Characterization of carbohydrate binding proteins in Trypanosoma cruzi

Trypanosoma cruzi is an obligatory intracellular protozoan parasite that causes Chagas' disease in humans and invades a great variety of mammalian cells. The nature of the ligand(s) and receptor components in both T. cruzi and target cells remains controversial, although it seems to involve an interaction with oligosaccharides. In an attempt to identify possible ligands on the parasite, we have searched for the presence of carbohydrate binding proteins (CBPs) in T. cruzi. By fluorescence-activated cell sorter analysis using a panel of fluoresceinated glyco- and neoglycopeptides with well characterized glycans, the presence of at least two different CBPs was identified on the surface of T. cruzi epimastigotes and trypomastigotes. The specificity of binding of the two CBPs seems to be mediated by galactose and mannose residues. The mannose- and galactose-mediated CBPs from epimastigotes and trypomastigotes were purified to homogeneity by affinity chromatography on immobilized thyroglobulin and identified as 60-70-kDa glycoproteins. Purified CBPs were able to specifically bind with high affinity to murine and human macrophages as well as other cell types susceptible to infection by T. cruzi but not to fat or neuronal cells. This binding was inhibited by the corresponding ligands. Moreover, the mannose-mediated CBP binding was completely abolished by alpha-mannosidase treatment of the cells. These results suggest a possible role for the CBPs in the recognition events between the parasite and target cells and/or in the interaction of the epimastigotes with the insect gut cells.

Fast purification of Phaseolus vulgaris isolectins

Phytohemagglutinin from red kidney bean has been purified by affinity chromatography on a human alpha 1-acid glycoprotein Sepharose 4B column. Further purification of the hemagglutinin's five isolectins was achieved on a Mono S column with an 86% protein recovery. Each sequentially eluted isolectin from the ion exchange column displayed either hemagglutinating or mitogenic activity. The main activity of each fraction was the result of the combination of varying proportions of the L and E subunits.

Characterization of isolectins in Tetracarpidium conophorum seeds (Nigerian walnut)

A lectin preparation obtained from Tetracarpidium conophorum (Nigerian walnut) by affinity chromatography of seed extracts on lactose-agarose has been shown to contain two components by gel filtration on Sephadex G150. The larger component Tetracarpidium conophorum agglutinin I (TCAI) is a disulphide-bonded 70 kDa homodimer whereas the second component TCAII is a 34 kDa monomeric protein. Amino terminal aminoacid sequencing shows identity in TCAI and TCAII for the first fifteen residues after which the sequences diverge. The N-terminal sequences of TCAI and TCAII show identity with sequences in the B-chains of ricin and Ricinus communis agglutinin I (RCAI) in eleven of the initial fifteen residues. Thereafter TCAI appears to be homologous to the ricin B chain whereas TCAII is more homologous with the B chain of RCAI. A limited screening of the carbohydrate-binding specificity of TCAII by affinity chromatography of defined oligosaccharides on TCAII Sepharose columns shows that the binding specificity reported earlier for affinity purified Tetracarpidium conophorum isolectins (Sato S, Animashaun T, Hughes RC (1991) J Biol Chem 266:11485-94) reflects the binding properties of TCAII which is the major isolectin in unfractionated lectin preparations.

Interaction of immobilized recombinant mouse C-type macrophage lectin with glycopeptides and oligosaccharides

Inflammatory and tumoricidal macrophages express galactose- and N-acetylgalactosamine-specific Ca(2+)-dependent lectins on their surfaces. This lectin is a family member of membrane-bound C-type animal lectins and consists of 304 amino acid residues (molecular weight 34,595). In the present study, expression vectors containing a nucleotide sequence corresponding to the carbohydrate-binding domain of mouse macrophage lectin cDNA have been prepared. The carbohydrate-binding specificity of the recombinant macrophage lectin expressed in Escherichia coli was investigated by comparing elution profiles of various glycopeptides having defined carbohydrate structures on immobilized lectins. When elution profiles of high mannose-type and complex-type Asn-linked carbohydrate chains were compared, the degree of retardation from immobilized macrophage lectin column was in the order tetraantennary complex-type with terminal galactosyl residues > triantennary complex-type with terminal galactosyl residues > biantennary complex-type with terminal galactosyl residues > high mannose-type glycopeptides. N-Terminal octapeptides from human glycophorin A that bore three NeuAc alpha 2-3Gal beta 1-3(NeuAc alpha 2-6)GalNAc serine/threonine-linked tetrasaccharide chains and their sequentially deglycosylated derivatives were also applied to this column. Glycopeptides carrying three constitutive GalNAc-Ser/Thr(Tn-antigen) had the strongest affinity, whereas those with fully sialylated carbohydrate tetrasaccharide chains showed weak interaction. The association kinetics of Asn-linked glycopeptides from bovine asialofetuin to recombinant macrophage lectin was determined by surface plasmon resonance spectroscopy. The results indicate k(assoc) value of 1.63 x 10(4) M-1 s-1. The calculated value for Ka was 6.20 x 10(7) M.

Strong affinity of Maackia amurensis hemagglutinin (MAH) for sialic acid-containing Ser/Thr-linked carbohydrate chains of N-terminal octapeptides from human glycophorin A

The interaction of the Maackia amurensis hemagglutinin (MAH) with various glycopeptides and oligosaccharides was investigated by means of immobilized lectin affinity chromatography. An amino terminal octapeptide obtained from human glycophorin A having three Neu5Ac alpha 2-->3Gal beta 1-->3(Neu5Ac alpha 2-->6)GalNAc tetrasaccharide chains, designated as CB-II, was found to have an extremely strong affinity for MAH. Therefore, it is strongly suggested that hemagglutination by MAH was caused by its interaction with Ser/Thr-linked carbohydrate chains of human glycophorin A on erythrocyte membranes.

Two-dimensional mapping of N-glycosidically linked asialo-oligosaccharides from glycoproteins as reductively pyridylaminated derivatives using dual separation modes of high-performance capillary electrophoresis

N-Glycosidically linked oligosaccharides were released from glycoproteins by digestion with trypsin followed by hydrazinolysis and subsequently re-N-acetylated and reductively pyridylaminated. Derivatives of sialic acid-containing oligosaccharides were further desialylated with neuraminidase. The final derivatives of asialo-oligosaccharides were analyzed by capillary zone electrophoresis in two carriers, an acidic phosphate buffer and an alkaline borate buffer. The former carrier allowed direct zone electrophoresis as cationic immonium ions, accordingly size-dependent separation, whereas the latter realized indirect electrophoresis as anionic borate complexes, i.e., separation based on the structural variation in outermost monosaccharide residues. Two-dimensional plots of relative mobilities of the derivatives in these dual separation modes to reductively pyridylaminated glucose provided a good tool for identification of oligosaccharides.

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.

The combination of normal phase with reversed phase high performance liquid chromatography for the analysis of asparagine-linked neutral oligosaccharides labelled with p-aminobenzoic ethyl ester

We have developed a novel approach for the analysis of asparagine-linked neutral oligosaccharides derived from glycoproteins. The oligosaccharides are labelled with p-aminobenzoic ethyl ester and the derivatives are separated on two high performance liquid chromatographic columns, one containing amide-silica and the other containing octadecyl-silica. The elution positions of 39 different ABEE-oligosaccharides on the two columns were plotted on a two-dimensional map. Unique non-overlapping positions of these oligosaccharides demonstrate that this technology would be useful for the identification of Asn-linked oligosaccharides at high sensitivity.

Purification and characterization of Canavalia gladiata agglutinin

A lectin from Japanese jack bean (Canavalia gladiata agglutinin, CGA) was purified by affinity chromatography on a maltamyl-Sepharose column. On sodium dodecyl sulfate-poly(acrylamide) gel electrophoresis, CGA was shown to have a protein subunit with a mol. wt. of 30,000. CGA has an amino acid composition similar to that of Concanavalin A. The lectin activity of CGA could be detected not only by hemagglutination assay with trypsinized human erythrocytes but also by the binding assay with intact horseradish peroxidase. The binding method could determine CGA in a concentration ranging from 50 to 500 ng/mL. The quantitative-inhibition studies of the binding indicated that CGA has sugar-binding specificities similar to those of concanavalin A.