Use of lectins in analysis of glycoconjugates

The use of mass spectrometry for the proteomic analysis of glycosylation

Of all protein PTMs, glycosylation is by far the most common, and is a target for proteomic research. Glycosylation plays key roles in controlling various cellular processes and the modifications of the glycan structures in diseases highlight the clinical importance of this PTM. Glycosylation analysis remains a difficult task. MS, in combination with modern separation methodologies, is one of the most powerful and versatile techniques for the structural analysis of glycoconjugates. This review describes methodologies based on MS for detailed characterization of glycoconjugates in complex biological samples at the sensitivity required for proteomic work.

High-sensitivity profiling of glycoproteins from human blood serum through multiple-lectin affinity chromatography and liquid chromatography/tandem mass spectrometry

We report here the use of high-performance lectin affinity enrichment of glycoproteins at microscale levels using a series of silica-bound lectins. The potential of this approach is being demonstrated for the glycoprotein enrichment from microliter volumes of human blood serum. Individual injections of sample to the affinity microcolumns packed with four lectin materials with different glycan specificities (Con A, SNA-I, UEA-I, PHA-L), followed by off-line reversed-phase pre-fractionation and nano-LC/MS/MS, permitted identification of 108 proteins in the lectin-bound fractions spanning a concentration dynamic range of 7-10 orders of magnitude. In contrast, multi-lectin microcolumn affinity chromatography, an alternative enrichment approach allowed identification of only 67 proteins. An attractive feature of high-performance lectin affinity chromatography at microscale levels is the substantial reduction of sample losses that are commonly experienced with extensive sample preparation needed for larger sample volumes.

Molecular forms of human prostate-specific antigen in urine of subjects with benign prostatic hyperplasia

In the present study, we examined mollecular forms of urinary prostate-specific antigen (PSA), focusing on its structural complexity in general and specifically on its microheterogeneity in relation to benign prostatic hyperplasia (BPH). Gel filtration, ion-exchange chromatography, and lectin-affinity chromatography were used to characterize PSA. In comparing the binding pattern of PSA isoforms, moderate changes were observed in the relative abundance of distinct molecular subpopulations separated on lectin-affinity columns. They may be related to alteration in the position and type of linkage of fucose or sialic acid, as well as to modification of the trimannosyl core by branching of the PSA oligosaccharide chain.

New hyphenated methodologies in high-sensitivity glycoprotein analysis

High-sensitivity glycoprotein analyses are of particular interest in modern biomedical and clinical research, as well as in the development of recombinant protein products. The evolution of new hyphenated methodologies in high-sensitivity glycoprotein analysis is highlighted in this thematic review. These methodologies include, in particular, capillary LC/MALDI/TOF/TOF MS in conjunction with online permethylation platform, and silica-based lectin microcolumns interfaced to MS. The potential of these methodologies in glycomic and glycoproteomic analysis is demonstrated for model glycoproteins as well as total glycomes and glycoproteomes derived from biological samples. Additionally, the applications of CE-MS, CEC, and nanoLC with graphitized carbon in the areas of glycomics and glycoproteomics are described.

Combining lectin microcolumns with high-resolution separation techniques for enrichment of glycoproteins and glycopeptides

Silica-based lectin microcolumns are described in this study together with the chemical procedures necessary for their preparation. The analytical merits of Canavalia ensiformis and Sambucus nigra lectins, [immobilized on activated macroporous silica], such as binding capacity, trapping reproducibility, and substrate selectivity, have been evaluated using model glycoproteins. The described microcolumns are applicable to high-pressure analytical schemes utilizing microvalving procedures, washing steps, and quantitative desorption for LC/MS analysis. The described analytical systems are amenable to the applications aiming at fractionation of complex glycopeptide mixtures and determination of the sites of glycosylation.

Core fucosylation of N-linked glycans in leukocyte adhesion deficiency/congenital disorder of glycosylation IIc fibroblasts

Leukocyte adhesion deficiency/congenital disorder of glycosylation IIc (LAD II/CDG IIc) is a genetic disease characterized by a decreased expression of fucose in glycoconjugates, resulting in leukocyte adhesion deficiency and severe morphological and neurological abnormalities. The biochemical defect is a reduced transport of guanosine diphosphate-L-fucose (GDP-L-fucose) from cytosol into the Golgi compartment, which reduces its availability as substrate for fucosyltransferases. The aim of this study was to determine the effects of a limited supply of GDP-L-fucose inside the Golgi on core fucosylation (alpha1,6-fucose linked to core N-acetylglucosamine [GlcNAc]) of N-linked glycans in LAD II fibroblasts. The results showed that, although [3H]fucose incorporation was generally reduced in LAD II cells, core fucosylation was affected to a greater extent compared with other types of fucosylation of N-linked oligosaccharides. In particular, core fucosylation was found to be nearly absent in biantennary negatively charged oligosaccharides, whereas other types of structures, in particular triantennary neutral species, were less affected by the reduction. Expression and activity of alpha1,6-fucosyltransferase (FUT8) in control and LAD II fibroblasts were comparable, thus excluding the possibility of a decreased activity of the transferase. The data obtained confirm that the concentration of GDP-L-fucose inside the Golgi can differentially affect the various types of fucosylation in vivo and also indicate that core fucosylation is not dependent only on the availability of GDP-L-fucose, but it is significantly influenced by the type of oligosaccharide structure. The relevant reduction in core fucosylation observed in some species of oligosaccharides could also provide clues for the identification of glycans involved in the severe developmental abnormalities observed in LAD II.

Molecular forms and microheterogeneity of the oligosaccharide chains of pregnancy-associated CA125 antigen

BACKGROUND

The cancer antigen CA125 has a very complex molecular architecture in terms of both protein backbone and oligosaccharide chains. In this study, we examined the molecular forms and microheterogeneity of oligosaccharide chains of pregnancy-associated CA125, as a first step towards gaining an insight into its possible involvement as a ligand in carbohydrate-dependent interactions. The glycobiochemical properties of CA125 may be of diagnostic and biomedical importance as specific markers of physiological and pathological conditions of early pregnancy, as well as targets in different therapeutic procedures.

METHODS

Pregnancy-associated CA125 was characterized by gel filtration and ion-exchange chromatography, followed by lectin-affinity chromatography with a panel of plant lectins as ligands.

RESULTS

CA125 antigen isolated from first trimester placental extract was found to be heterogeneous in respect to molecular mass and the existence of different glyco-isoforms. Thus, elution profiles from the lectin-affinity columns demonstrated molecular subpopulations bound with low, intermediate and high affinity. Under the applied experimental conditions, CA125 bound most strongly to Triticum vulgaris agglutinin (WGA) and Ricinus communis agglutinin (RCA), but low affinity interactions occurred with the other lectins tested.

CONCLUSIONS

The assessment of the carbohydrate composition of N- and O-glycans of pregnancy-associated CA125 was in general agreement with available data on CA125 of cancer origin. The main difference was observed in reactivity to Canavalia ensiformis agglutinin (ConA) and Phaseolus vulgaris erythroagglutinin (PHA-E) binding.

Glycosylation of urinary prostate-specific antigen in benign hyperplasia and cancer: assessment by lectin-binding patterns

OBJECTIVES

In the present study, we examined the glycosylation of urinary prostate-specific antigen (PSA) from benign prostatic hyperplasia (BPH) and prostate cancer (PCa) subjects, specifically looking at alterations in its oligosaccharide chain as a potential biomarker of these pathophysiological conditions.

DESIGN AND METHODS

First morning urine voids were collected from subjects with PCa and BPH before initiation of any treatment. Urinary PSA was characterized by ion-exchange chromatography, followed by lectin affinity chromatography on the columns using immobilized plant lectins.

RESULTS

Four isoforms of urinary PSA from both BPH and PCa samples were separated by ion-exchange chromatography. The elution profiles from lectin-affinity columns reflected molecular heterogeneity of PSA isoforms and the main differences observed were in the reactivity to Ulex europaeus agglutinin, Aleuria aurantia agglutinin, Phaseolus vulgaris erythroagglutinin and Phaseolus vulgaris leukoagglutinin.

CONCLUSIONS

The observed differences in the lectin reactivities between BPH PSA and PCa PSA may be of clinical importance in the evaluation of prostate health.

Elevation of the level and activity of acid ceramidase in Alzheimer's disease brain

Protein glycosylation modifies the processing of several key proteins involved in the molecular pathogenesis of Alzheimer's disease (AD). Aberrant glycosylation of tau and down-regulation of sialyltransferase in AD brain suggest a possible dysregulation of protein glycosylation that may play a role in AD. We therefore isolated major glycoproteins from AD brain by using lectin-affinity chromatographies and ion-exchange chromatography and further separated them using SDS-polyacylamide gel electrophoresis. Mass spectrometry analysis of 11 isolated glycoproteins led to their identification as: neuronal cell adhesion molecule, beta-globin, IgM heavy chain VH1 region precursor, contactin precursor, dipeptidylpeptidase VI, CD81 partner 3, prenylcysteine lyase, adipocyte plasma-associated protein, acid ceramidase and two novel proteins. We found that the level and activity of acid ceramidase (AC), one of the major identified human brain glycoproteins, were significantly elevated in AD brain. Immunohistochemical staining indicated that AC was located mainly in the cell bodies of neurons and colocalized with neurofibrillary tangles. Our findings suggest that AC might play a role in controlling neuronal apoptosis and that AC-mediated signalling pathways might be involved in the molecular mechanism of AD.

Chicken growth hormone: further characterization and ontogenic changes of an N-glycosylated isoform in the anterior pituitary gland

Glycosylation is one of the post-translational modifications that growth hormone (GH) can undergo. This has been reported for human, rat, mouse, pig, chicken and buffalo GH. The nature and significance of GH glycosylation remains to be elucidated. This present study further characterizes glycosylated chicken GH (G-cGH) and examines changes in the pituitary concentration of G-cGH during embryonic development and post hatching growth. G-cGH was purified from chicken pituitaries by affinity chromatography (Concanavalin A-Sepharose and monoclonal antibody bound to Sepharose). Immunoreactive G-cGH has a MW of 26 kDa or 29 kDa as determined by SDS-PAGE, respectively, under non-reducing and reducing conditions. Evidence that it is N-glycosylated comes from its susceptibility to peptide N-glycosidase F, and its resistance to O-glycosidase. Based on the ability of G-cGH to bind Concanavalin A or wheat germ agglutinin but not other lectins and its susceptibility to peptide N-glycosidase F, a hybrid or biantennary type glycopeptide (GlcNac2, Man) structure is proposed. Some G-cGH can be observed in the pituitary at most ages examined (from 15-day embryo to adult). Moreover, electron microscopy revealed the presence of both immuno-reactive GH and Concanavalin A-reactive sites in the same secretory granules in the somatotrope. There were marked changes in the level and relative proportion of G-cGH in the pituitary gland during development and growth, the proportion of G-cGH rising during late embryonic development (e.g., between 15 and 18 days of development) and with further increases between 9 weeks and 15 weeks old. G-cGH was able to bind to chicken liver membrane preparations with less affinity than non-glycosylated monomer; on the other hand, however, G-cGH stimulated cell proliferation on Nb2 lymphoma bioassay whereas the non-glycosylated monomer was uncapable to do it.

Differentiation of Fonsecaea pedrosoi mycelial forms into sclerotic cells is induced by platelet-activating factor

Platelet-activating factor (PAF) has been shown to induce the differentiation of several cell types. In this work, we evaluated the effects of PAF on the formation of sclerotic cells of Fonsecaea pedrosoi, the major causative agent of chromoblastomycosis. Cell differentiation was evaluated by light and electron microscopy, which showed that treatment of mycelial forms with PAF results in the generation of sclerotic bodies with typical morphological characteristics. Biochemical features of PAF-induced sclerotic cells were also analyzed and compared with those from sclerotic forms induced by propranolol, a previously described differentiating agent of F. pedrosoi. Chemical analyses of lipid and carbohydrate components from PAF- or propranolol-induced sclerotic bodies revealed that palmitic, stearic, oleic and linoleic acids were the major fatty acid components, while glucose, mannose, galactose and rhamnose were detected as the principal sugar constituents in these cells. Surface carbohydrate components of PAF- and propranolol-induced sclerotic cells were also evaluated, by flow cytometry analysis with twelve different lectins. The profile of reactivity of PAF- or propranolol-induced fungal cells with lectins was also very similar. Hydrolysis of the synthetic substrate p-nitrophenylphosphate by fungal cells demonstrated that the addition of PAF or propranolol to the mycelial cultures similarly promotes a significant increase in ecto-phosphatase activity. These results indicate that the differentiation of F. pedrosoi mycelial cells induced by PAF generates authentic sclerotic forms, as confirmed by the analysis of morphological and biochemical attributes. Since PAF is synthesized in normal conditions by the human host, these observations may have a correlation with the differentiation of F. pedrosoi in vivo.

Small-scale analysis of O-linked oligosaccharides from glycoproteins and mucins separated by gel electrophoresis

A technique with subpicomolar sensitivity was developed for analyzing O-linked oligosaccharides released from glycoproteins separated by gel electrophoresis. The protocol involves gel electrophoresis, electroblotting to poly-(vinylidene fluoride) membrane, reductive beta-elimination, and analysis of released oligosaccharides by liquid chromatography coupled to negative ion electrospray mass spectrometry. It was also found that N-linked oligosaccharides could be recovered under the same conditions, found both as free oligosaccharides and as distinct glycopeptides created from reductive cleavage of the protein backbone, giving some information on site-specific glycosylation. The method was used to demonstrate that the difference between human alpha-2HS-glycoprotein isoforms separated by 2D-gel electrophoresis was partially due to sialylation of both O-linked and N-linked oligosaccharides. It was also shown that both acidic and neutral oligosaccharides could be recovered and analyzed simultaneously from high molecular mass (200,000-5,000,000 Da) highly glycosylated mucin glycoproteins collected from small intestine and saliva and separated by sodium dodecyl sulfate-agarose/polyacrylamide composite gels. Mass spectrometric data not only gave information about the mass distribution of the heterogeneous mixtures of oligosaccharides from [M - xH](x-) ions but also gave information about the isomeric heterogeneity of the oligosaccharides from their resolution by porous graphitized carbon chromatography. Tandem mass spectrometry was explored as a technique for distinguishing between oligosaccharide isomers with different sequences and also between oligosaccharides with the same sequence but with different linkage configurations.

Genetically altered mice with different sialyltransferase deficiencies show tissue-specific alterations in sialylation and sialic acid 9-O-acetylation

Glycan chains on glycoconjugates traversing the Golgi apparatus are often terminated by sialic acid residues, which can also be 9-O-acetylated. This process involves competition between multiple Golgi enzymes. Expression levels of Golgi enzyme mRNAs do not always correlate with enzyme activity, which in turn cannot accurately predict glycan sequences found on cell surfaces. Here we examine the cell type-specific expression of terminal glycans in tissues of normal mice in comparison with animals deficient in ST6Gal-I (transfers alpha2-6-linked sialic acid to Galbeta1-4GlcNAc) or ST3Gal-I (transfers alpha2-3-linked sialic acid to Galbeta1-3GalNAc). Tissues of ST6Gal-I null mice showed minimal binding of an alpha2-6-sialic acid-specific lectin, indicating that no other enzyme generates Siaalpha2-6Galbeta1-4GlcNAc and that Siaalpha2-6GalNAc (sialyl-Tn) is rare in mice. However, exposed Galbeta1-4GlcNAc termini were only moderately increased, indicating that these can be partially capped by other enzymes. Indeed, Galalpha1-3Galbeta1-4GlcNAc and Fucalpha1-2Galbeta1-4GlcNAc termini were enhanced in some tissues. Many tissues of ST3Gal-I null animals showed increases in Galbeta1-3GalNAc termini, and some increases in poly-N-acetyllactosamines. However, overall expression of alpha2-3-linked sialic acid was selectively reduced only in a few instances, indicating that other ST3Gal enzymes can generate this linkage in most tissues. Highly selective losses of 9-O-acetylation of sialic acid residues were also observed, with ST6Gal-I deficiency causing loss on endothelium and ST3Gal-I deficiency giving a marked decrease on CD4(+) lymphocytes. These data demonstrate selective regulation of sialylation and 9-O-acetylation, point to cell types with potential physiological defects in null animals, and show in vivo evidence for competition between Golgi enzymes.

Congenital disorders of glycosylation type Ig is defined by a deficiency in dolichyl-P-mannose:Man7GlcNAc2-PP-dolichyl mannosyltransferase

Type I congenital disorders of glycosylation (CDG I) are diseases presenting multisystemic lesions including central and peripheral nervous system deficits. The disease is characterized by under-glycosylated serum glycoproteins and is caused by mutations in genes encoding proteins involved in the stepwise assembly of dolichol-oligosaccharide used for protein N-glycosylation. We report that fibroblasts from a type I CDG patient, born of consanguineous parents, are deficient in their capacity to add the eighth mannose residue onto the lipid-linked oligosaccharide precursor. We have characterized cDNA corresponding to the human ortholog of the yeast gene ALG12 that encodes the dolichyl-P-Man:Man(7)GlcNAc(2)-PP-dolichyl alpha6-mannosyltransferase that is thought to accomplish this reaction, and we show that the patient is homozygous for a point mutation (T571G) that causes an amino acid substitution (F142V) in a conserved region of the protein. As the pathological phenotype of the fibroblasts of the patient was largely normalized upon transduction with the wild type gene, we demonstrate that the F142V substitution is the underlying cause of this new CDG, which we suggest be called CDG Ig. Finally, we show that the fibroblasts of the patient are capable of the direct transfer of Man(7)GlcNAc(2) from dolichol onto protein and that this N-linked structure can be glucosylated by UDP-glucose:glycoprotein glucosyltransferase in the endoplasmic reticulum.

Microscale nonreductive release of O-linked glycans for subsequent analysis through MALDI mass spectrometry and capillary electrophoresis

A new beta-elimination-based procedure has been devised for a microscale release of O-linked oligosaccharides from glycoproteins. Unlike the conventional Carlson degradation, which leads to formation of alditols, the procedure reported here renders the reducing end intact. Conversion of the liberated oligosaccharides to glycosylamines in ammonia medium is followed by the production of the reducing oligosaccharides through the addition of boric acid. The quantitatively generated oligosaccharides with the reducing end can subsequently be derivatized with a fluorophoric reagent for capillary electrophoresis or, alternatively, analyzed through MALDI mass spectrometry. The microscale version of these chemical steps permits us to investigate structurally O-linked oligosaccharides at very low levels.

Human T cell activation induces the expression of a novel CD45 isoform that is analogous to murine B220 and is associated with altered O-glycan synthesis and onset of apoptosis

Activated T cells undergo changes during their transition to T cell blasts and, subsequently, via a phase of anergy, to apoptosis. For example, activated murine T cell blasts express the B-cell-specific CD45R isoform, B220, a marker also present on T cells in mice and humans with defective Fas-mediated apoptosis in vivo, suggesting a role for B220 up-regulation in the transition of activation to apoptosis. Human T cells, activated in vitro with superantigens and mitogens, also express B220 as they undergo blastogenesis and cell cycle progression. B220 expression peaks on T cells undergoing apoptosis. CD43-hexasaccharide glycoform expression and lectin binding profiles indicate that B220 expression is reflective of altered O-linked glycan biosynthesis found in specific T cell subsets transitioning through the phases of proliferation, anergy, and apoptosis. Potential implications of these alterations include changes in lymphocyte adhesion and trafficking and homeostasis through altered sensitivity to Fas-dependent and independent pathways of apoptosis.

TcR-alpha/beta(+) CD4(-)CD8(-) T cells in humans with the autoimmune lymphoproliferative syndrome express a novel CD45 isoform that is analogous to murine B220 and represents a marker of altered O-glycan biosynthesis

Autoimmune lymphoproliferative syndrome (ALPS), caused by inherited defects in apoptosis secondary to mutations in genes encoding Fas/CD95/APO-1 and Fas ligand (Fasl)/CD95L, is characterized by nonmalignant lymphadenopathy and splenomegaly, increased T cell receptor alpha/beta(+) CD4(-)CD8(-) T cells (alpha/beta(+) double-negative T cells [alpha/beta(+)-DNT cells]), autoimmunity, hypergammaglobulinemia, and cytokine abnormalities. The alpha/beta(+)-DNT cells are immunophenotypically and functionally similar to alpha/beta(+)-DNT cells that accumulate in lpr and gld mice, which bear genetic mutations in Fas and FasL. In these mice, alpha/beta(+)-DNT cells express the B-cell-specific CD45R isoform B220. We show that alpha/beta(+)-DNT cells of ALPS patients, with either Fas or FasL mutations, also express B220. In addition, also similar to LPR/gLD mice, they have an unusual population of B220-positive CD4(+) T cells. B220 expression, together with our finding of characteristic lectin binding profiles, demonstrates that cell surface O-linked glycoproteins have undergone specific modifications, which may have consequences for lymphocyte trafficking, cell-cell interactions, and access to alternative apoptosis pathways.

Sugar-lectin interactions investigated through affinity capillary electrophoresis

The affinity interactions of Concanavalin A (Con A) with various saccharide oligomers (dextrins, dextrans, and selected N-linked glycans from various glycoproteins) have been investigated through a capillary electrophoresis approach. Con A has shown a notable binding discrimination between the alpha-1,6-linked dextran and alpha-1,4-linked dextrin oligomers. Both the binding capacity and binding discrimination appear to decrease with an increase in sugar chainlength. While the core structure of N-linked glycans is deemed to be responsible for the overall binding of various glycans to Con A, the presence of mannose units at the non-reducing ends was found to be very beneficial to the affinity interaction with Con A. Finally, a connection between the glycan-lectin interaction and glycoprotein-lectin interaction has also been suggested.

An arabinogalactan protein(s) is a key component of a fraction that mediates local intercellular communication involved in tracheary element differentiation of zinnia mesophyll cells

Local intercellular communication is involved in tracheary element (TE) differentiation of zinnia (Zinnia elegans L.) mesophyll cells and mediated by a proteinous macromolecule, which was designated xylogen. To characterize and isolate xylogen, a bioassay system to monitor the activity of xylogen was developed, in which mesophyll cells were embedded in microbeads of agarose gel at a low (2.0-4.3x10(4) cells ml(-1)) or high density (8.0-9.0x10(4) cells ml(-1)) and microbeads of different cell densities were cultured together in a liquid medium to give a total density of 2.1-2.5x10(4) cells ml(-1). Without any additives, the frequency of TE differentiation was much smaller in the low-density microbeads than in the high-density microbeads. This low level of TE differentiation in the low-density microbeads was attributable to the shortage of xylogen. When cultures were supplemented with conditioned medium (CM) prepared from zinnia cell suspensions undergoing TE differentiation, the frequency of TE differentiation in the low-density microbeads increased remarkably, indicating the activity of xylogen in the CM. The xylogen activity in CM was sensitive to proteinase treatments. Xylogen was bound to galactose-specific lectins such as Ricinus communis agglutinin and peanut agglutinin, and precipitated by beta-glucosyl Yariv reagent. These results indicate that xylogen is a kind of arabinogalactan protein.

Studies on the structure of a lithium-treated soybean pectin: characteristics of the fragments and determination of the carbohydrate substituents of galacturonic acid

Two galacturonic-acid-containing polysaccharide fractions (ChSS and P) were isolated from soybean meal and subjected to lithium treatment. The fragments obtained were analyzed by using monosaccharide and methylation analyses, and NMR spectroscopy. Lithium degradation of ChSS, followed by sodium borodeuteride reduction, hydrolysis, sodium borohydride reduction, and acetylation afforded alditol acetates, of which the labeled ones reflected residues linked to GalA. As followed from quantifications of the labeled and non-labeled alditols from each constituent monosaccharide by GLC-EIMS, 6 mol% of Ara, 22 mol% of Fuc, 13 mol% of Gal, 53 mol% of Rha, and 57 mol% of Xyl are glycosidically linked to GalA. Analysis of the lithium-treated polymer revealed that it contains arabinogalactan side chains linked to Rha O-4, which consist of a beta-(1 --> 4)-linked galactan substituted with highly branched arabinan chains. On average, an arabinogalactan chain contains up to 29 Gal and 25 Ara residues. Surface plasmon resonance was used to determine conditions for affinity chromatography. Furthermore, this technique confirmed the presence of terminal alpha-Fuc residues in ChSS. Polysaccharide P turned out to be relatively resistant to lithium degradation.

One-step synthesis of biotinyl photoprobes from unprotected carbohydrates

A simple and versatile approach for the preparation of carbohydrate photoprobes has been developed. By a single-step reaction at 37 degrees C, a biotinylated carbene-generating unit was introduced to the reducing end of unprotected carbohydrates. Micromole quantities of N-acetyllactosamine, Lewis X trisaccharide, and sialyl Lewis X tetrasaccharide were easily converted to their biotinylated photoreactive analogues, which enabled the nonradioisotopic chemiluminescent detection of the photolabeled products. Thus, a sequence of lectin photoaffinity labeling, from the probe synthesis to the detection of labeled protein, was readily accomplished within one week. Our strategy may be applicable to any aldehyde-bearing ligand.

Binding of Clostridium botulinum C2 toxin to asparagine-linked complex and hybrid carbohydrates

Clostridium botulinum C2 toxin is a binary toxin composed of an enzymatic subunit (C2I) capable of ADP-ribosylating actin and a binding subunit (C2II) that is responsible for interaction with receptors on eukaryotic cells. Here we show that binding of C2 toxin depends on the presence of asparagine-linked carbohydrates. A recently identified Chinese hamster ovary cell mutant (Fritz, G., Schroeder, P., and Aktories, K. (1995) Infect. Immun. 63, 2334-2340) was found to be deficient in N-acetylglucosaminyltransferase I. C2 sensitivity of this mutant was restored by transfection of an N-acetylglucosaminyltransferase I cDNA. C2 toxin sensitivity was reduced after inhibition of alpha-mannosidase II. In contrast, Chinese hamster ovary cell mutants deficient in sialylated (Lec2) or galactosylated (Lec8) glycoconjugates showed an increase in toxin sensitivity compared with wild-type cells. Our results show that the GlcNAc residue linked beta-1,2 to the alpha-1,3-mannose of the asparagine-linked core structure is essential for C2II binding to Chinese hamster ovary cells.

Lectinochemical characterization of a GalNAc and multi-Galbeta1-->4GlcNAc reactive lectin from Wistaria sinensis seeds

An agglutinin that has high affinity for GalNAcbeta1-->, was isolated from seeds of Wistaria sinensis by adsorption to immobilized mild acid-treated hog gastric mucin on Sepharose 4B matrix and elution with aqueous 0.2 M lactose. The binding property of this lectin was characterized by quantitative precipitin assay (QPA) and by inhibition of biotinylated lectin-glycan interaction. Of the 37 glycoforms tested by QPA, this agglutinin reacted best with a GalNAcbeta1-->4 containing glycoprotein (GP) [Tamm-Horsfall Sd(a+) GP]; a Galbeta1-->4GlcNAc containing GP (human blood group precursor glycoprotein from ovarian cyst fluid and asialo human alpha1-acid GP) and a GalNAcalpha1-->3GalNAc containing GP (asialo bird nest GP), but poorly or not at all with most sialic acid containing glycoproteins. Among the oligosaccharides tested, GalNAcalpha1-->3GalNAcbeta1-->3Galalpha1-->4Galbeta 1-->4Glc (Fp) was the most active ligand. It was as active as GalNAc and two to 11 times more active than Tn cluster mixtures, Galbeta1--> 3/4GlcNAc (I/II), GalNAcalpha1-->3(L-Fucalpha1-->2)Gal (Ah), Galbeta1-->4Glc (L), Galbeta1-->3GalNAc (T) and Galalpha1--> 3Galalpha-->methyl (B). Of the monosaccharides and their glycosides tested, p-nitrophenyl betaGalNAc was the best inhibitor; it was approximately 1.7 and 2.5 times more potent than its corresponding alpha anomer and GalNAc (or Fp), respectively. GalNAc was 53.3 times more active than Gal. From the present observations, it can be concluded that the Wistaria agglutinin (WSA) binds to the C-3, C-4 and C-6 positions of GalNAc and Gal residues; the N-acetyl group at C-2 enhances its binding dramatically. The combining site of WSA for GalNAc related ligands is most likely of a shallow type, able to recognize both alpha and beta anomers of GalNAc. Gal ligands must be Galbeta1-->3/4GlcNAc related, in which subterminal beta1-->3/4 GlcNAc contributes significantly to binding; hydrophobicity is important for binding of the beta anomer of Gal. The decreasing order of the affinity of WSA for mammalian structural carbohydrate units is Fp >/= multi-II > monomeric II >/= Tn, I and Ah >/= E and L > T > Gal.

Characterization of the carbohydrate binding specificity and kinetic parameters of lectins by using surface plasmon resonance

An accurate, rapid, and sensitive method for characterizing the carbohydrate binding properties of lectins using a BIAcore apparatus and the detection method of surface plasmon resonance is described. As a model study, the sialic acid binding lectins from Sambucus nigra and Maackia amurensis, which are specific for the epitopes Neu5Ac(alpha2-6)Gal and Neu5Ac(alpha2-3)Gal, respectively, were chosen as suitable candidates. Two systems, one for the analysis of oligosaccharides and the other for glycoproteins, were developed after a rigorous analysis and evaluation of such parameters as binding conditions, buffers, and regeneration conditions. The systems take into account nonspecific binding, using the respective denatured lectin as negative blank, and avoid loss of activity: regeneration of the surface using either 10 mM NaOAc (pH 4.3) buffer (oligosaccharide system) or 20 mM HCl (glycoprotein system). The specificity of the lectins is well illustrated, while the kinetics parameters are shown to be sensitive to subtle changes in the recognized epitopes, and to be affected by steric hindrance. Surface plasmon resonance is a suitable technique for the analysis and characterization of lectins.

Leukocyte adhesion deficiency II syndrome, a generalized defect in fucose metabolism

Leukocyte adhesion deficiency II has been described in only 2 patients; herein we report extensive investigation of another patient. The physical stigmata were detected during prenatal ultrasonographic investigation. Sialyl-Lewis X (sLex) was absent from the surface of polymorphonuclear neutrophils, and cell binding to E- and P-selectin was severely impaired, causing an immunodeficiency. The elevation of peripheral neutrophil counts occurred within several days after birth. A severe hypofucosylation of glycoconjugates bearing fucose in different glycosidic links was present in all cell types investigated, demonstrating that leukocyte adhesion deficiency II is not only a disorder of leukocytes but a generalized inherited metabolic disease affecting the metabolism of fucose.

Preparation and isolation of neoglycoconjugates using biotin-streptavidin complexes

Glycoproteins commercially available in multi-gram quantities, were used to prepare milligram amounts of neoglycoproteins. The glycoproteins bromelain and bovine gamma-globulin were proteolyzed to obtain glycopeptides or converted to a mixture of glycans through hydrazinolysis. The glycan mixture was structurally simplified by carbohydrate remodeling using exoglycosidases. Glycopeptides were biotinylated using N-hydroxysuccinimide activated-long chain biotin while glycoprotein-derived glycans were first reductively aminated with ammonium bicarbonate and then biotinylated. The resulting biotinylated carbohydrates were structurally characterized and then bound to streptavidin to afford neoglycoproteins. The peptidoglycan component of raw, unbleached heparin (an intermediate in the manufacture of heparin) was similarly biotinylated and bound to streptavidin to obtain milligram amounts of a heparin neoproteoglycan. The neoglycoconjugates prepared contain well defined glycan chains at specific locations on the streptavidin core and should be useful for the study of protein-carbohydrate interactions and affinity separations.

Lectin from Beauveria bassiana mycelium recognizes Thomsen-Friedenreich antigen and related structures

A lectin was isolated from the mycelium of the stationary growing enthomopathogenic fungus Beauveria bassiana by extraction, chromatography on QAE-Sephadex A-25, salt precipitation, and hydrophobic chromatography on Phenyl-Sepharose 4B. The Beauveria bassiana lectin (BBL) is a 15 kDa glycoprotein rich in hydrophobic amino acids, without detectable amount of methionine. It contains 12.6% of carbohydrates including galactose and mannose. Isoelectric point was found at pH 7.1. The lectin is stable between pH 6 and 11, and at temperature under 50 degrees C. The activity of the lectin was not dependent on with Ca++, Mn++, Mg++ cations and was apparently not blood group ABO specific. The hemagglutination caused by the lectin was inhibited by alpha lactose (Gal beta 1-->4 Glc alpha), but not by beta lactose (Gal beta 1-->4 Glc beta). In direct ELISA the BBL preferentially reacted with some glycoproteins carrying O-linked sugar structure Gal beta 1-->3 GalNAc: strongly with human glycophorin A and weaker with mouse glycophorin, fetuin, IgA, ovine submaxillary mucin. On the other hand BBL did not react in direct ELISA with N-glycoproteins (alpha 1-acid glycoprotein, haptoglobin, fibronectin), however, N-glycoproteins could act as inhibitors of lectin-glycophorin A interaction. We observed also weak interaction with asialo-Tamm-Horsfall N-glycoprotein having unusual large, branched N-glycans with outer GalNAc beta 1-->4Gal sequence. Moreover, the interaction of BBL with highly sialylated preparations of glycoproteins was weaker than with asialo forms. Presented results indicate that BBL exhibits sugar binding specificity towards glycotope corresponding to Thomsen-Friedenreich antigen and its related sequences: Gal beta 1-->3 GalNAc > Neu Ac alpha 2-3 Gal beta 1-->3 (Neu Ac alpha 2-6) GalNAc > Gal beta 1-->4 Glc alpha.

Cell surface sialic acid and the regulation of immune cell interactions: the neuraminidase effect reconsidered

It has been known for over a decade that sialidase (neuraminidase) treatment could substantially enhance the capacity of resting B cells to stimulate the proliferation of allogeneic and antigen specific, syngeneic T cells. Thus, cell-surface sialic acid was implicated as a potential modulator of immune cell interaction. However, little progress has been made in either identifying explicit roles for sialic acid in this system or in hypothesizing mechanisms to explain the "neuraminidase effect." Here we show for the first time that cell surface sialic acid on medium incubated B cells blocks access to costimulatory molecules on the B cell surface, and that this is the most likely explanation for the neuraminidase effect. Further, we show that it is likely to be upregulation of ICAM-1 and its subsequent engagement of LFA-1 rather than loss of cell surface sialic acid that in part regulates access to CD86 and other costimulatory molecules. However, we cannot exclude a role for CD86-bound sialic acid on the B cell in modulating binding to T cell CD28. Because sialidase treatment of resting B cells but not resting T cells enables T cell activation, we suggest that sialidase treatment may still be an analogue for an authentic step in B cell activation, and show that for highly activated B cells (activated with polyclonal anti-IgM plus INF-gamma) there is specific loss 2, 6-linked sialic acid. Potential roles for sialic acid in modulating B cell/T cell collaboration are discussed.

Mouse C127 cells transfected with fucosyltransferase fuc-TIII express masked Lewisx but not Lewisx antigen

To study human alpha1,3/1,4fucosyltransferase (Fuc-TIII) as an alpha1,3 fucosyltransferase, we constructed two cell clones, C127-FT and C127-T-FT, by transfecting cDNA in parental (C127) or Polyoma T antigen expressing (C127-T) mouse cells, respectively. Both C127-FT and C127-T-FT clones express high levels of a fucosyltransferase activity kinetically similar to Fuc-TIII and an RNA that is amplified by a Fuc-TIII-specific oligonucleotide primer pair after reverse transcription. Clone C127-FT is Lewisxpositive, by flow cytometry, only after alpha-galactosidase or sialidase treatment, and releases [3H]Fuc N-glycans which efficiently bind to immobilized Griffonia simplicifolia I and Sambucus nigra lectins. Immunoblotting confirms that C127-FT glycoproteins acquire Lewisxreactivity only after specific deglycosylation, and shows that a small subset of Griffonia simplicifolia I isolectin B4reactive glycoproteins bears masked Lewisx, suggesting fine substrate recognition by Fuc-TIII. Moreover, transient transfection of H type alpha1, 2fucosyltransferase in clone C127-T-FT directs synthesis of Lewisyantigen, as detected by flow cytometry. Results indicate that Fuc-TIII expressed in C127 cells synthesizes masked Lewisxantigen while Lewisxantigen is not detectable.

Structural requirements of carbohydrates to bind Agaricus bisporus lectin

Galbeta1-3GalNAc (T-disaccharide) and related molecules were assayed to describe the structural requirements of carbohydrates to bind Agaricus bisporus lectin (ABL). Results provide insight into the most relevant regions of T-disaccharide involved in the binding of ABL. It was found that monosaccharides bind ABL weakly indicating a more extended carbohydrate-binding site as compared to those involvedin the T-disaccharide specific lectins such as jacalin and peanut agglutinin. Lacto-N-biose (Galbeta1-3GlcNAc) unlike T-disaccharide, is unable to inhibit the ABL interaction, thus showing the great importance of the position of the axial C-4 hydroxyl group of GalNAc in T-disaccharide. This finding could explain the inhibitory ability of Galbeta1-6GlcNAc and lactose because C-4 and C-3 hydroxyl groups of reducing Glc, respectively, occupy a similar position as reported by conformational analysis. From the comparison of different glycolipids bearing terminal T-disaccharide bound to different linkages, it can be seen than ABL binding is even more impaired by an adjacent C-6 residual position than by the anomeric influence of T-disaccharide. Furthermore, the addition of beta-GlcNAc to the terminal T-disaccharide in C-3 position of Gal does not affect the ABL binding whereas if an anionic group such as glucuronic acid is added to C-3, the binding is partially affected. These findings demonstrate that ABL holds a particular binding nature different from that of other T-disaccharide specific lectins.

Simplified procedure for fractionation and structural characterisation of complex mixtures of N-linked glycans, released from HIV-1 gp120 and other highly glycosylated viral proteins

HIV-1 gp120 is heavily glycosylated containing 24 N-glycosylation sites, and this makes elucidation of the significance of glycans at individual glycosylation sites a difficult task. A procedure is described where a complex mixture of biologically radiolabelled glycans of gp120, derived from a relatively small number of virus-infected cells may be characterized by a combination of N-glycanase release, single lectin separation, and normal phase HPLC (NP-HPLC). The method was applied in analysis of three N-linked glycosylation sites essential for the in vivo priming of T-cells, specific for an epitope in their vicinity (Sjölander, S., Bolmstedt, A., Akerblom, 1996. Virology 215, 124-133.). The carbohydrate compositions of wild type gp120 and of mutant variants gp120 lacking one, two, or all of these three active N-linked glycans were analysed. Cells were infected with r-vaccinia virus expressing wild-type gp120 or mutated gp120, or were infected with HIV-1BRU (wild type) or mutant virus variants. HIV-1 glycoproteins were purified by immunosorbent affinity chromatography and released glycans were separated on lectins, then analysed with NP-HPLC. Our data showed that the structural composition of glycans occupying two of the three glycosylation sites was heterogeneous but the site located adjacent to the T-cell epitope was equipped with one large, high mannose-type structure (> 11 units) with the capacity to cover a substantial part of the gp120 surface.

Glycoaffinity chromatography and biological recognition

The potential of bioaffinity chromatography as a tool for study of biological recognition mechanisms is gaining increasing recognition. Biochromatographic methods allow the separation of proteins according to both the structure of their polypeptidic chain and their post-translational modifications. Among the various post-translational modifications which proteins undergo, glycosylation has conducted to the development of original methods (glycotechnologies). This review discusses the applications of glycotechnologies in bioaffinity chromatography, and particularly the use of biochromatography to elucidate mechanisms involved in glycobiology.

A study of glycoconjugates in nasopharyngeal carcinoma with correlation to clinical transformation

Little is known about the glycoconjugate changes in human nasopharyngeal epithelium following neoplastic changes. Glycoconjugate histochemistry (Glycine maximus (SBA), Griffonia simplicifolia II (GSA-II), Ulex europaeus (UEA-I), Arachis hypogaea (PNA) and Canavalia ensiformis (ConA)) were performed on the following nasopharyngeal biopsies: 10 adenoid tissues (benign controls), 10 chronic inflammation, 20 squamous metaplasia, 20 undifferentiated carcinoma and 5 squamous cell carcinoma. These results were correlated with the clinical transformations findings. Strong ConA and PNA staining (after neuraminidase treatment (NA)) characterized a subpopulation of squamous metaplasia subjects who later transformed to nasopharyngeal carcinoma. Strong ConA and PNA (before and after NA) depicted the majority of undifferentiated carcinoma subjects having local recurrence following irradiation therapy. In squamous metaplasia, ConA and PNA (after NA) staining may serve as a warning sign for neoplastic changes. Strong stainings for ConA and PNA (before and after NA) in undifferentiated carcinoma subjects may predict a risk for local recurrence.

An IgG monoclonal antibody against Dictyostelium discoideum glycoproteins specifically recognizes Fucalpha1,6GlcNAcbeta in the core of N-linked glycans. Localized expression of core-fucosylated glycoconjugates in human tissues

Core fucosylation of N-linked oligosaccharides (GlcNAcbeta1, 4(Fucalpha1,6)GlcNAcbeta1-Asn) is a common modification in animal glycans, but little is known about the distribution of core-fucosylated glycoproteins in mammalian tissues. Two monoclonal antibodies, CAB2 and CAB4, previously raised against carbohydrate epitopes of Dictyostelium discoideum glycoproteins (Crandall, I. E. and Newell, P. C. (1989) Development 107, 87-94), specifically recognize fucose residues in alpha1,6-linkage to the asparagine-bound GlcNAc of N-linked oligosaccharides. These IgG3 antibodies do not cross-react with glycoproteins containing alpha-fucoses in other linkages commonly seen in N- or O-linked sugar chains. CAB4 recognizes core alpha1,6 fucose regardless of terminal sugars, branching pattern, sialic acid linkage, or polylactosamine substitution. This contrasts to lentil and pea lectins that recognize a similar epitope in only a subset of these structures. Additional GlcNAc residues found in the core of N-glycans from dominant Chinese hamster ovary cell mutants LEC14 and LEC18 progressively decrease binding. These antibodies show that many proteins in human tissues are core-fucosylated, but their expression is localized to skin keratinocytes, vascular and visceral smooth muscle cells, epithelia, and some extracellular matrix-like material surrounding subpopulations of lymphocytes. The availability of these antibodies now allows for an extended investigation of core fucose epitope expression in development and malignancy and in genetically manipulated mice.

Engineering proteins that bind to cell surface carbohydrates

Carbohydrate residues covalently linked to plasma membrane proteins and lipids often provide specific markers at the cell surface. Traditionally such carbohydrate structures have been identified using antibodies and lectins. However problems of affinity and lack of specificity have restricted their usefulness. Protein engineering offers a way round these difficulties. In the case of some specialised cell surface carbohydrate structures, such as polysialic acid, enzymes may be useful analytical tools. Endosialidases specific for polysialic acid have recently been cloned and sequenced.

Study of the enzymatic transformation of fluorescently labeled oligosaccharides in human epidermoid cells using capillary electrophoresis with laser-induced fluorescence detection

Isomeric oligosaccharides of both beta Gal(1-->3)beta GlcNAc (type I) series and beta Gal(1-->4)beta GlcNAc (type II) series were studied by using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. A mixture of phenylboronic acid and sodium tetraborate was used in the CE running buffers to improve the electrophoretic separation of the oligosaccharides. Both series of the tetramethylrhodamine (TMR)-labeled substrates [beta Gal(1-->3)beta GlcNAc-O-TMR and beta Gal(1-->4)beta GlcNAc-O-TMR) and their potential enzymatic products were baseline resolved using CE. The high resolution provided by CE and the excellent detection limit (8.10(-23) mol, or 50 molecules) by LIF allowed for the determination of minor enzyme products in the presence of excess unreacted substrate. The action of competing enzymes acting on the common type I sequence was monitored after the incubation of human epidermoid carcinoma cells (A431) with a fluorescent substrate (beta Gal(1-->3)beta GlcNAc-O-TMR). The CE-LIF analyses showed the formation of both synthetic and hydrolytic products, suggesting the actions of glycosyltransferases and glycosidases in the cells.

New approaches in clinical chemistry: on-line analyte concentration and microreaction capillary electrophoresis for the determination of drugs, metabolic intermediates, and biopolymers in biological fluids

The use of capillary electrophoresis (CE) for clinically relevant assays is attractive since it often presents many advantages over contemporary methods. The small-diameter tubing that holds the separation medium has led to the development of multicapillary instruments, and simultaneous sample analysis. Furthermore, CE is compatible with a wide range of detectors, including UV-Vis, fluorescence, laser-induced fluorescence, electrochemistry, mass spectrometry, radiometric, and more recently nuclear magnetic resonance, and laser-induced circular dichroism systems. Selection of an appropriate detector can yield highly specific analyte detection with good mass sensitivity. Another attractive feature of CE is the low consumption of sample and reagents. However, it is paradoxical that this advantage also leads to severe limitation, namely poor concentration sensitivity. Often high analyte concentrations are required in order to have injection of sufficient material for detection. In this regard, a series of devices that are broadly termed 'analyte concentrators' have been developed for analyte preconcentration on-line with the CE capillary. These devices have been used primarily for non-specific analyte preconcentration using packing material of the C18 type. Alternatively, the use of very specific antibody-containing cartridges and enzyme-immobilized microreactors have been demonstrated. In the current report, we review the likely impact of the technology of capillary electrophoresis and the role of the CE analyte concentrator-microreactor on the analysis of biomolecules, present on complex matrices, in a clinical laboratory. Specific examples of the direct analysis of physiologically-derived fluids and microdialysates are presented, and a personal view of the future of CE in the clinical environment is given.

Glycosylation of bile-salt-stimulated lipase from human milk: comparison of native and recombinant forms

Bile-salt-stimulated lipase (BSSL) is an enzyme present in human milk. BSSL is important for fat digestion in infants. It contains one site for N-glycosylation and a serine/threonine-rich domain which is highly O-glycosylated. Both N- and O-linked sugar chains were studied on native BSSL from three donors and compared to the glycosylation of recombinant BSSL produced in Chinese hamster ovary or mouse fibroblast (C-127) cell lines. The carbohydrate composition of oligosaccharides was mapped using sugar and methylation analyses, enzyme-linked immunosorbant assay, and different separation techniques. Native BSSL was found to be highly glycosylated (19-26%). It contained a high amount of fucosylated oligosaccharides and expressed both Lewis a and Lewis b blood group antigens. None of the recombinant BSSL forms contained fucose. N-linked structures on native BSSL were identified as mainly mono- and disialylated biantennary complex type structures with or without fucose substitution. High-pH anion-exchange chromatography analysis indicated that the recombinant forms of BSSL contained similar types of N-glycan structures differing mainly in their content of sialic acid and by the absence of fucose residues. Native BSSL contained predominantly large O-linked oligosaccharides. This was in contrast to the recombinant forms of BSSL which contained mainly short type O-glycans with a high content of sialic acid. Interestingly, the estimated number of O-glycans attached to native BSSL was lower than that for the recombinant forms.

Purification and analysis of a polydnavirus gene product expressed using a poly-histidine baculovirus vector

The VHv1.1 polydnavirus gene has been implicated in suppressing the encapsulation response in parasitized insects [Li and Webb (1994) J. Virol. 68, 7482-7489]. In order to characterize this gene product and to further our analysis of its immunosuppressive function, we expressed the VHv1.1 using a custom-designed C-terminal poly-histidine baculovirus vector which allows for high expression and single-step purification of the protein. The 34 kDa VHv1.1 protein was expressed in baculovirus-infected cell cultures and in H. virescens larvae. Highly enriched preparations of the secreted VHv1.1 protein were obtained after affinity chromatography using a NTA-(Ni2+) resin. Characterization with purified preparations of the VHv1.1 protein established that the protein is N-glycosylated, containing glycogroups which are PNGase F-sensitive but Endo H-resistant. The recombinant VHv1.1 protein bound to hemocytes in vitro and in vivo and was endocytosed in a manner similar to the native protein produced in CsPDV-infected larvae.

Developmental regulation of a pregnancy-specific oligosaccharide structure, NeuAcalpha2,6GalNAcbeta1,4GlcNAc, on select members of the rat placental prolactin family

Successful pregnancy is dependent upon an array of signaling proteins secreted by the trophoblast cells of the placenta. Among these is a group of proteins related to pituitary prolactin, known as the prolactin/growth hormone family. These proteins are expressed at specific times during gestation and synthesized in distinct trophoblast cell types in the rat placenta. We report here that select members of this family, prolactin-like protein (PLP-A), PLP-B, PLP-C, decidual/trophoblast PRP, and placental lactogen I variant, only which are expressed in the spongiotrophoblast, late in rat placental development bear Asn-linked oligosaccharides terminating with NeuAcalpha2,6GalNAcbeta1,4GlcNAcbeta-R. This reflects the concurrent expression of these prolactin/growth hormone family members with the peptide-specific beta1,4GalNAc-transferase and an alpha2,6-sialyltransferase, which can add sialic acid to terminal beta1,4-linked GalNAc. We have determined that at least one of the prolactin-like proteins, PLP-A, is recognized by the protein-specific GalNAc-transferase. The presence of NeuAcalpha2, 6GalNAcbeta1,4GlcNAcbeta-R on only a limited number of glycoproteins synthesized by the spongiotrophoblasts between mid gestation and birth reflects the need for both the GalNAc-transferase and the peptide recognition determinant for efficient addition of GalNAc. Thus, expression of the GalNAc-transferase and specific members of the prolactin/growth hormone family is developmentally regulated in the rat placenta, suggesting a physiological role for the terminal NeuAcalpha2,6GalNAcbeta1,4GlcNAcbeta-R sequence on Asn-linked oligosaccharides of these proteins.

Immobilized Lotus tetragonolobus agglutinin binds oligosaccharides containing the Le(x) determinant

A defined set of oligosaccharides and glycopeptides containing alpha-linked fucose were used to examine the specificity of the immobilized fucose-binding lectin Lotus tetragonolobus agglutinin (LTA1), also known as lotus lectin. Glycans containing the Lewis x determinant (Le(x)) Gal beta 1-4[Fuc alpha 1-3]GlcNAc beta 1-3-R were significantly retarded in elution from high density LTA-Emphaze columns. The lectin also bound the fucosylated lacdiNAc trisaccharide GalNAc beta 1-4[Fuc alpha 1-3]GlcNAc. The lectin did not bind glycans containing either sialylLe(x) or VIM-2 determinants, nor did it bind the isomeric Le(x), Gal beta 1-3[Fuc alpha 1-4]GlcNAc-R. Although 2'-fucosyllactose Fuc alpha 1-2Gal beta 1-4Glc) was retarded in elution from the columns, larger glycans containing the H-antigen Fuc alpha 1-2Gal beta 1-3(4)GlcNAc-R interacted poorly with immobilized LTA. Our results demonstrate that immobilized LTA is effective in isolating glycans containing the Le(x) antigen and is useful in analyzing specific fucosylation of glycoconjugates.

Purification and characterization of Kurloff cell sialoglycoproteins with acid phosphatase activity

The major alpha 2-6 sialoglycoproteins in detergent-extracts of Kurloff cells were purified by anion-exchange and Sambucus nigra agglutinin-affinity chromatographies. The similar ultrastructural localisations of (1) S. nigra agglutinin-gold conjugates and (2) acid phosphatase activities on the Kurloff body and particularly on its myelin figures indicated that the major alpha 2-6 sialoglycoproteins of the Kurloff cell had acid phosphatase activity. Two-dimensional electrophoresis showed that these tartrate-sensitive phosphatases corresponded to 2 acidic (pI 3.4-3.7) polypeptides of 36 and 34 kDa. Hydrolysis with peptide-N-glycosidases F gave a 33 kDa apoprotein rich in alanine, glutamic acid, tyrosine and lysin. A lectin-affinity study demonstrated that they contained hybrid type bisected and fucosylated N-linked oligosaccharides. Cytotoxic properties were previously attributed to Kurloff cells and other studies suggested that not only acid phosphatases but also alpha 2-6-linked sialic acid residues themselves may participate in natural killer activity.