Concanavalin A interactions with asparagine-linked glycopeptides. Bivalency of bisected complex type oligosaccharides

Insight into Erythrina Lectins: Properties, Structure and Proposed Physiological Significance

The genus Erythrina, collectively known as “coral tree”, are pantropical plants, comprising of more than 112 species. Since the early 1980s, seven of these have been found to possess hemagglutinating activity, although not yet characterized. However, around two dozen galactose-binding lectins have been isolated and fully characterized with respect to their sugar specificity, glycoconjugates agglutination, dependence of activity on metal ions, primary and secondary structures and stability. Three lectins have been fully sequenced and the crystal structures of the two proteins have been solved with and without the haptenic sugar. Lectins isolation and characterization from most of these species usually originated from the seeds, although the proteins from other vegetative tissues have also been reported. The main objective of this review is to summarize the physicochemical and biological properties of the reported purified Erythrina lectins to date. Structural comparisons, based on available lectins sequences, are also made to relate the intrinsic physical and chemical properties of these proteins. Particular attention is also given to the proposed biological significance of the lectins from the genus Erythrina.

The Emerging Importance of IgG Fab Glycosylation in Immunity

Human IgG is the most abundant glycoprotein in serum and is crucial for protective immunity. In addition to conserved IgG Fc glycans, ∼15-25% of serum IgG contains glycans within the variable domains. These so-called "Fab glycans" are primarily highly processed complex-type biantennary N-glycans linked to N-glycosylation sites that emerge during somatic hypermutation. Specific patterns of Fab glycosylation are concurrent with physiological and pathological conditions, such as pregnancy and rheumatoid arthritis. With respect to function, Fab glycosylation can significantly affect stability, half-life, and binding characteristics of Abs and BCRs. Moreover, Fab glycans are associated with the anti-inflammatory activity of IVIgs. Consequently, IgG Fab glycosylation appears to be an important, yet poorly understood, process that modulates immunity.

Online combination of reversed-phase/reversed-phase and porous graphitic carbon liquid chromatography for multicomponent separation of proteomics and glycoproteomics samples

In this paper, we describe an online combination of reversed-phase/reversed-phase (RP-RP) and porous graphitic carbon (PGC) liquid chromatography (LC) for multicomponent analysis of proteomics and glycoproteomics samples. The online RP-RP portion of this system provides comprehensive 2-D peptide separation based on sequence hydrophobicity at pH 2 and 10. Hydrophilic components (e.g. glycans, glycopeptides) that are not retained by RP are automatically diverted downstream to a PGC column for further trapping and separation. Furthermore, the RP-RP/PGC system can provide simultaneous extension of the hydropathy range and peak capacity for analysis. Using an 11-protein mixture, we found that the system could efficiently separate native peptides and released N-glycans from a single sample. We evaluated the applicability of the system to the analysis of complex biological samples using 25 μg of the lysate of a human choriocarcinoma cell line (BeWo), confidently identifying a total of 1449 proteins from a single experiment and up to 1909 distinct proteins from technical triplicates. The PGC fraction increased the sequence coverage through the inclusion of additional hydrophilic sequences that accounted for up to 6.9% of the total identified peptides from the BeWo lysate, with apparent preference for the detection of hydrophilic motifs and proteins. In addition, RP-RP/PGC is applicable to the analysis of complex glycomics samples, as demonstrated by our analysis of a concanavalin A-extracted glycoproteome from human serum; in total, 134 potentially N-glycosylated serum proteins, 151 possible N-glycosylation sites, and more than 40 possible N-glycan structures recognized by concanavalin A were simultaneously detected.

Elucidation of N-glycosylation sites on human platelet proteins: a glycoproteomic approach

Among known platelet proteins, a prominent and functionally important group is represented by glycoprotein isoforms. They account e.g. for secretory proteins and plasma membrane receptors including integrins and glycoprotein VI as well as intracellular components of cytosol and organelles including storage proteins (multimerin 1 etc.). Although many of those proteins have been studied for some time with regard to their function, little attention has been paid with respect to their glycosylation sites. Here we report the analysis of N-glycosylation sites of human platelet proteins. For the enrichment of glycopeptides, lectin affinity chromatography as well as chemical trapping of protein bound oligosaccharides was used. Therefore, concanavalin A was used for specific interaction with carbohydrate species along with periodic acid oxidation and hydrazide bead trapping of glycosylated proteins. Derivatization by peptide:N-glycosidase F yielded deglycosylated peptides, which provided the basis for the elucidation of proteins and their sites of modification. Using both methods in combination with nano-LC-ESI-MS/MS analysis 70 different glycosylation sites within 41 different proteins were identified. Comparison with the Swiss-Prot database established that the majority of these 70 sites have not been specifically determined by previous research projects. With this approach including hydrazide bead affinity trapping, the immunoglobulin receptor G6f, which is known to couple to the Ras-mitogen-activated protein kinase pathway in the immune system, was shown here for the first time to be present in human platelets.

The role of weak protein-protein interactions in multivalent lectin-carbohydrate binding: crystal structure of cross-linked FRIL

Binding of multivalent glycoconjugates by lectins often leads to the formation of cross-linked complexes. Type I cross-links, which are one-dimensional, are formed by a divalent lectin and a divalent glycoconjugate. Type II cross-links, which are two or three-dimensional, occur when a lectin or glycoconjugate has a valence greater than two. Type II complexes are a source of additional specificity, since homogeneous type II complexes are formed in the presence of mixtures of lectins and glycoconjugates. This additional specificity is thought to become important when a lectin interacts with clusters of glycoconjugates, e.g. as is present on the cell surface. The cryst1al structure of the Glc/Man binding legume lectin FRIL in complex with a trisaccharide provides a molecular snapshot of how weak protein-protein interactions, which are not observed in solution, can become important when a cross-linked complex is formed. In solution, FRIL is a divalent dimer, but in the crystal FRIL forms a tetramer, which allows for the formation of an intricate type II cross-linked complex with the divalent trisaccharide. The dependence on weak protein-protein interactions can ensure that a specific type II cross-linked complex and its associated specificity can occur only under stringent conditions, which explains why lectins are often found forming higher-order oligomers.

The crystal structures of Man(alpha1-3)Man(alpha1-O)Me and Man(alpha1-6)Man(alpha1-O)Me in complex with concanavalin A

The crystal structures of concanavalin A in complex with Man(alpha1-6)Man(alpha1-O)Me and Man(alpha1-3)Man(alpha1-O)Me were determined at resolutions of 2.0 and 2.8 A, respectively. In both structures, the O-1-linked mannose binds in the conserved monosaccharide-binding site. The O-3-linked mannose of Man(alpha1-3)Man(alpha1-O)Me binds in the hydrophobic subsite formed by Tyr-12, Tyr-100, and Leu-99. The shielding of a hydrophobic surface is consistent with the associated large heat capacity change. The O-6-linked mannose of Man(alpha1-6)Man(alpha1-O)Me binds in the same subsite formed by Tyr-12 and Asp-16 as the reducing mannose of the highly specific trimannose Man(alpha1-3)[Man(alpha1-6)]Man(alpha1-O)Me. However, it is much less tightly bound. Its O-2 hydroxyl makes no hydrogen bond with the conserved water 1. Water 1 is present in all the sugar-containing concanavalin A structures and increases the complementarity between the protein-binding surface and the sugar, but is not necessarily a hydrogen-bonding partner. A water analysis of the carbohydrate-binding site revealed a conserved water molecule replacing O-4 on the alpha1-3-linked arm of the trimannose. No such water is found for the reducing or O-6-linked mannose. Our data indicate that the central mannose of Man(alpha1-3)[Man(alpha1-6)]Man(alpha1-O)Me primarily functions as a hinge between the two outer subsites.

Electron microscopy and x-ray diffraction studies of Lotus tetragonolobus A isolectin cross-linked with a divalent Lewisx oligosaccharide, an oncofetal antigen

The interactions of lectins with multivalent carbohydrates often leads to the formation of highly ordered cross-linked lattices that are amenable to structural studies. A particularly well ordered, two-dimensional lattice is formed from fucose-specific isolectin A from Lotus tetragonolobus cross-linked with difucosyllacto-N-neohexaose, an oligosaccharide possessing the Lewisx determinant, which is an oncofetal antigen. A combination of electron microscopy, x-ray diffraction, simulation of electron micrographs, and molecular model building was used to determine the relative positions of the tetrameric lectin and bivalent carbohydrate within the lattice. X-ray diffraction from unoriented pellets was used to determine the lattice dimensions and analysis of electron micrographs was used to determine the lattice symmetry. Molecular models of the lattice were constructed based on the known structure of the jack bean lectin concanavalin A and the high degree of sequence homology between the two lectins. Using the symmetry and dimensions of the lattice and its appearance in filtered electron micrographs, molecular models were used to determine the orientation of the lectin in the lattice, and to define the range of lectin-oligosaccharide interactions consistent with the structural data. The present study provides the first description of a highly ordered, two-dimensional, cross-linked lattice between a tetravalent lectin and a bivalent carbohydrate.

Garlic (Allium sativum) lectins bind to high mannose oligosaccharide chains

Two mannose-binding lectins, Allium sativum agglutinin (ASA) I (25 kDa) and ASAIII (48 kDa), from garlic bulbs have been purified by affinity chromatography followed by gel filtration. The subunit structures of these lectins are different, but they display similar sugar specificities. Both ASAI and ASAIII are made up of 12.5- and 11.5-kDa subunits. In addition, a complex (136 kDa) comprising a polypeptide chain of 54 +/- 4 kDa and the subunits of ASAI and ASAIII elutes earlier than these lectins on gel filtration. The 54-kDa subunit is proven to be alliinase, which is known to form a complex with garlic lectins. Constituent subunits of ASAI and ASAIII exhibit the same sequence at their amino termini. ASAI and ASAIII recognize monosaccharides in mannosyl configuration. The potencies of the ligands for ASAs increase in the following order: mannobiose (Manalpha1-3Man) < mannotriose (Manalpha1-6Manalpha1-3Man) approximately mannopentaose << Man9-oligosaccharide. The addition of two GlcNAc residues at the reducing end of mannotriose or mannopentaose enhances their potencies significantly, whereas substitution of both alpha1-3- and alpha1-6-mannosyl residues of mannotriose with GlcNAc at the nonreducing end increases their activity only marginally. The best manno-oligosaccharide ligand is Man9GlcNAc2Asn, which bears several alpha1-2-linked mannose residues. Interaction with glycoproteins suggests that these lectins recognize internal mannose as well as bind to the core pentasaccharide of N-linked glycans even when it is sialylated. The strongest inhibitors are the high mannose-containing glycoproteins, which carry larger glycan chains. Indeed, invertase, which contains 85% of its mannose residues in species larger than Man20GlcNAc, exhibited the highest binding affinity. No other mannose- or mannose/glucose-binding lectin has been shown to display such a specificity.

The glycosylated enzyme-binding assay for the study of the interaction of free and immobilized lectins with carbohydrates

The glycosylated enzymes (invertase and glucose oxidase) were used as the competitive markers for a simple and rapid determination of the lectin-saccharide interactions. The method, based on the formation of the conjugate of an appropriate glycoenzyme with the specific carbohydrate-binding lectins and the inhibition of the conjugate formation with a monosaccharide, was described. This method was used to estimate the relative carbohydrate specificity of Concanavalin A for monosaccharides derived from D-mannose. The inhibition effect of the saccharides on the formation of Concanavalin A-glycosylated enzyme precipitate was compared with their influence on the enzyme sorption on conjugate Concanavalin A-bead cellulose support. The amount of the interacting enzyme was estimated either indirectly from its concentration in a supernatant that was determined spectrophotometrically (Con A was in a free or immobilized form) or directly in the immobilized form linked to Con A-sorbent using the flow microcalorimetric method. The results obtained, using different methods, agreed in general.

A comparison of the fine saccharide-binding specificity of Dioclea grandiflora lectin and concanavalin A

The lectin from the seeds of Dioclea grandiflora (DGL) is a Man/Glc-specific tetrameric protein with physical and saccharide-binding properties reported to be similar to that of the jack bean lectin concanavalin A (ConA). Unlike other plant lectins, both DGL and ConA bind with high affinity to the core trimannoside moiety, 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, which is present in all asparagine-linked carbohydrates. In the present study, hemagglutination inhibition techniques have been used to investigate binding of DGL and ConA to a series of mono- and dideoxy analogs of methyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside and to a series of asparagine-linked oligomannose and complex oligosaccharides and glycopeptides. The results indicate that both DGL and ConA recognize epitopes on all three residues of the trimannoside: the 3-, 4-, and 6-hydroxyl groups of the alpha(1-6)Man residue, the 3-hydroxyl group of the alpha(1-3)Man residue, and the 2- and 4-hydroxyl groups of the central Man residue of the core trimannoside. However, unlike ConA, DGL does not bind to biantennary complex carbohydrates. This was confirmed by showing that biantennary complex glycopeptides do not bind to a DGL-Sepharose affinity column. Unlike ConA, DGL does not show enhanced affinity for a large N-linked oligomannose carbohydrate (Man9 glycopeptide) relative to the trimannoside. Thus, DGL and ConA share similar epitope recognition of the core trimannoside moiety. However, they exhibit differences in their fine specificities for larger N-linked oligomannose and complex carbohydrates.

Observation of unique cross-linked lattices between multiantennary carbohydrates and soybean lectin. Presence of pseudo-2-fold axes of symmetry in complex type carbohydrates

The tetrameric lectin from Glycine max (soybean) (SBA) has been shown to cross-link and precipitate with N-linked multiantennary complex type oligosaccharides containing nonreducing terminal Gal residues (Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041). In the present study, negative stain electron micrographs of the precipitates of SBA with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal Gal or GalNAc residues show the presence of highly ordered cross-linked lattices for many of the complexes. The precipitates of SBA with a "bisected" and "nonbisected" N-linked biantennary complex type oligosaccharide containing Gal residues at the nonreducing termini show similar two-dimensional patterns. However, the pattern observed for the precipitates of a tetraantennary complex type oligosaccharide with SBA is distinct from those of the two biantennary carbohydrates. Furthermore, the precipitates formed between the lectin and a synthetic O-linked biantennary ("cluster") glycoside with terminal GalNAc residues show a pattern that is different from those above. Four biantennary pentasaccharide analogs of the blood group I antigen containing beta-LacNAc moieties at the 2,3-, 2,4-, 2,6-, and 3,6-positions of the core Gal also showed ordered patterns in their precipitates with SBA. X-ray crystallographic data and mixed quantitative precipitation profiles of binary mixtures of the four analogs demonstrate that each analog possesses a unique cross-linked lattice with the protein. A common structural feature of the naturally occurring and synthetic carbohydrates that show highly organized cross-linked lattices with SBA is the presence of a pseudo-2-fold axis of symmetry in each oligosaccharide relating the terminal binding epitopes on each arm. This suggests that the symmetry features of certain naturally occurring branch chain oligosaccharides facilitate formation of highly ordered, homogeneous cross-linked complexes with specific lectins.

Cytochemical characterization of oligosaccharide side chains of the glycoproteins of rat zona pellucida: an ultrastructural study

BACKGROUND

The zona pellucida (ZP), an extracellular matrix which surrounds mammalian oocytes, is formed by different glycoproteins. Several studies have revealed that carbohydrate residues present in glycoproteins of ZP play a key role in the sperm-egg recognition. However, the origin and the biochemical composition of ZP remain to be completely resolved.

METHODS

ZP glycoproteins from rat ovarian follicles were investigated at light and electron microscopic level by the application of lectins conjugated to peroxidase, digoxigenin, and colloidal gold in combination with enzyme and chemical treatment. A quantitative analysis was also performed.

RESULTS

ZP shows reactivity to WGA, DSA, LFA, AAA, RCA I, and MAA. SBA and PNA showed a variable reactivity ranging from negative to strongly positive. A uniform pattern of binding throughout ZP was observed with DSA, Con A, AAA, MAA, and LFA. However, labeling by RCA I and SBA was higher in the outer ZP while PNA and WGA showed a higher binding in the inner ZP. Lectin reactivity was detected in cortical granules, endoplasmic reticulum, Golgi apparatus, vesicles, and multivesicular bodies of oocytes.

CONCLUSIONS

ZP contained the terminal disaccharides Gal beta 1,4GlcNAc, Gal beta 1,3GalNAc, and GalNAc beta 1,3Gal and the trisaccharides Neu5Ac alpha 2, 3Gal beta 1,4GlcNAc, Neu5Ac-Gal beta 1,3GalNAc, and Neu5Ac-GalNAc beta 1,3Gal sequences. The occurrence of Fucose residues alpha 1,6 linked to the inner core region of N-linked glycoproteins of ZP was demonstrated by the use of several fucose-specific lectins. Methylation-saponification treatment in combination with lectin cytochemistry reveals that Gal, GalNAc, and polyllactosamine residues of rat ZP glycoproteins contain sulphated groups. The reactivity observed in ooplasmic vesicles was similar to that of ZP, thus suggesting that the oocyte is the site of synthesis of ZP glycoproteins.

Observation of unique cross-linked lattices between multiantennary carbohydrates and soybean lectin. Presence of pseudo-2-fold axes of symmetry in complex type carbohydrates

The tetrameric lectin from Glycine max (soybean) (SBA) has been shown to cross-link and precipitate with N-linked multiantennary complex type oligosaccharides containing nonreducing terminal Gal residues (Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041). In the present study, negative stain electron micrographs of the precipitates of SBA with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal Gal or GalNAc residues show the presence of highly ordered cross-linked lattices for many of the complexes. The precipitates of SBA with a "bisected" and "nonbisected" N-linked biantennary complex type oligosaccharide containing Gal residues at the nonreducing termini show similar two-dimensional patterns. However, the pattern observed for the precipitates of a tetraantennary complex type oligosaccharide with SBA is distinct from those of the two biantennary carbohydrates. Furthermore, the precipitates formed between the lectin and a synthetic O-linked biantennary ("cluster") glycoside with terminal GalNAc residues show a pattern that is different from those above. Four biantennary pentasaccharide analogs of the blood group I antigen containing beta-LacNAc moieties at the 2.3-, 2.4-, 2.6-, and 3.6-positions of the core Gal also showed ordered patterns in their precipitates with SBA. X-ray crystallographic data and mixed quantitative precipitation profiles of binary mixtures of the four analogs demonstrate that each analog possesses a unique cross-linked lattice with the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural analysis of the carbohydrate chain of glycopeptides isolated from Robinia pseudoacacia seed lectins

Robinia pseudoacacia seeds contain lectins which are closely related. Pronase digestion of the dimeric and tetrameric lectins, RPA1 and RPA3, gave glycopeptides. The structure of the oligosaccharide was determined by 1H NMR spectroscopy and carbohydrate determination as alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-[alpha-D-Manp+ ++-(1-->6)]-beta- D-Manp-(1-->4)-beta-D-GlcpNAc-(1-->4)-[alpha-L-Fucp-(1-->3)] -beta-D-GlcpNAc - (1-->4)-Asn. It appears that the 34-kDa constitutive polypeptide of RPA1 contains 4-5 carbohydrate chains whereas the 30.5-kDa and 29-kDa subunits of RPA3 contain two and one oligosaccharide chains, respectively.

Formation of homogeneous carbohydrate-lectin cross-linked precipitates from mixtures of D-galactose/N-acetyl-D-galactosamine-specific lectins and multiantennary galactosyl carbohydrates

Quantitative precipitation studies have shown that the Man/Glc-specific lectin concanavalin A (ConA) forms homogeneous (homopolymeric) cross-linked precipitates with individual asparagine-linked oligomannose and bisected hybrid-type glycopeptides in the presence of binary mixtures of the carbohydrates [Bhattacharyya, L., Khan, M. I. & Brewer, C. F. (1988) Biochemistry 27, 8762-8767]. The results indicate that the ConA-glycopeptide precipitates are highly organized cross-linked lattices that are unique for each carbohydrate. Using similar techniques, the present study shows that the Gal-specific lectins from Erythrina indica and Ricinus communis (agglutinin I) form homogeneous cross-linked complexes with individual carbohydrates in binary mixtures of triantennary and tetraantennary complex-type oligosaccharides with terminal Gal residues. Conversely, binary mixtures of Gal/GalNAc-specific lectins from E. indica, Erythrina cristagalli, Erythrina flabelliformis, R. communis, soybean (Glycine max), and Wistaria floribunda (tetramer) in the presence of a naturally occurring or synthetic branched-chain oligosaccharide with terminal GalNAc or Gal residues provide evidence for the formation of separate cross-linked lattices between each lectin and the carbohydrate. The present results therefore demonstrate the formation of homogeneous lectin-carbohydrate cross-linked lattices in (a) a mixture of branched-chain complex-type oligosaccharides in the presence of a specific Gal/GalNAc-binding lectin, and (b) a mixture of lectins with similar physicochemical and carbohydrate binding properties in the presence of an oligosaccharide. These findings show that lectin-carbohydrate cross-linking interactions provide a high degree of specificity which may be relevant to their biological functions as receptors.

Interaction of linear manno-oligosaccharides with three mannose-specific bulb lectins. Comparison with mannose/glucose-binding lectins

Three new mannose-binding lectins, isolated from daffodil (NPA), amaryllis (HHA), and snowdrop (GNA) bulbs, are capable of precipitating with a linear mannopentaose (Man alpha 1-3Man alpha 1-3Man alpha 1-3Man alpha 1-2Man). NPA and HHA reacted strongly with the mannopentaose whereas GNA gave a precipitate only at concentrations greater than 500 microM. A phosphate group at C-6 of the nonreducing terminal mannosyl group prevented precipitation in all three cases. The reduced (NaBH4) mannopentaose, Man4Man-ol, did not precipitate with GNA or NPA, but was active with HHA. This activity was lost when Man4Man-ol was converted (NaIO4 then NaBH4; mild acid hydrolysis of the reduced product) into trisaccharide derivatives. With alpha-D-Manp-OMe the three lectins gave UV difference spectra having large positive peaks at 292-293 and 283-284 nm, and a small positive peak at 275 nm, characteristic of tryptophanyl and tyrosyl residues. The association constants for the interaction with alpha-D-Manp-OMe were very low (NPA, 86; HHA, 66; and GNA, 41 M-1), but the lectins bound methyl (1----3)-alpha-mannobioside with increased affinity (K for NPA 540, for HHA 2400, and for GNA 200 M-1). The bulb lectins lack binding sites for hydrophobic ligands, as judged by their failure to interact with the fluorescent probes 8-anilino-1-napthalenesulfonic acid (ANS) and 6-p-toluidino-2-naphthalenesulfonic acid (TNS).

Interactions of five D-mannose-specific lectins with a series of synthetic branched trisaccharides

The interaction of a series of synthetic, branched trisaccharides with five D-mannose-specific lectins was studied by precipitation-inhibition assay. The branched methyl alpha-D-mannotrioside, alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-alpha-D-Man pOMe, the best inhibitor of the Con A-Dextran interaction, was 42 times more potent than alpha-D-ManpOMe, and 3-6 times more potent than the two trisaccharides substituted with D-glucosyl groups, and 8-15 times those with D-galactosyl groups. Surprisingly, methyl O-alpha-D-mannopyranosyl-(1----3)-alpha-D-mannopyranoside was bound to Con A 8-fold more avidly than methyl alpha-D-mannopyranoside. However, the related pea lectin (PSA) was singularly different from Con A in its carbohydrate-binding activity, showing no significantly enhanced binding to any of the sugars examined. The trisacchrides containing terminal, nonreducing, (1----3)-linked alpha-D-mannopyranosyl groups, i.e., alpha-D-Manp-(1----3)-[alpha-D-Glep-(1----6)]alpha-D-Manp OMe, alpha-D-Manp-(1----3)]-alpha-D-Galp-(1----6)]-alpha-D-ManpOMe++ +, and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-alpha-D-Man pOMe, were the best inhibitors of the snowdrop lectin (GNA)-D-mannan precipitation system. On the other hand, all branched trisaccharides exhibited very similar inhibitory potencies toward the daffodil lectin (NPA)-D-mannan interaction, whereas alpha-D-Manp-(1----3)-[alpha-D-Galp-(1----6)]-alpha-D-ManpOMe++ + and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-alpha-D-Man pOMe were somewhat better inhibitors than the other branched trisaccharides of the amaryllis lectin (HHA)-D-mannan precipitation reaction. (ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of concanavalin A with glycoproteins. A quantitative precipitation study of concanavalin A with the soybean agglutinin

Certain oligomannose-type glycopeptides have been previously shown to be bivalent for binding to concanavalin A and capable of precipitating the lectin by forming homogeneous cross-linked lattices [L. Bhattacharyya, M. I. Khan, and C.F. Brewer, Biochemistry, 27 (1988) 8762-8767]. In the present study, the effect of protein environment on the binding properties of an oligomannose-type oligosaccharide has been examined through quantitative precipitation analysis of the interactions of concanavalin A (Con A) with the soybean (Glycine max) agglutinin (SBA), which is a tetrameric glycoprotein possessing a single Man9-oligomannose chain per monomer. The results showed that SBA forms two different types of cross-linked complexes with tetrameric Con A, depending on the relative ratio of the two molecules in solution. At a concentration of one equivalent or less, SBA forms a 1:1 complex with Con A. At concentrations exceeding one equivalent, SBA forms a 2:1 complex with Con A. However, SBA forms only 1:1 cross-linked complexes with dimeric forms of Con A, such as acetyl- and succinyl-Con A. The results demonstrated that the total valency of the carbohydrate of SBA is a function of both the quaternary structure of Con A, as well as the relative ratio of SBA to Con A. In addition, the individual Man9-oligosaccharide, which as a glycopeptide is bivalent for binding to Con A, expresses univalency when present on the protein matrix of SBA.

Differences in expression of oligosaccharide determinants by phenotypically distinct sublines of the Dunning 3327 rat prostate cancer

Oligosaccharides expressed by the 3327-H and 3327-MAT LyLu sublines of the Dunning rat prostate cancer model have been compared in formalin-fixed and routinely paraffin-embedded tumour tissues. Binding by lectins of defined specificity has been employed to identify expression of seven oligosaccharide structures by primary and metastatic prostatic carcinoma cells. Neuraminidase digestion was employed to reveal determinants masked by sialic acid. The presence of core Man alpha 1----3(Man alpha 1----6)Man beta 1----4GlcNAc beta 1----4 determinants recognised by Con-A (Canavalia ensiformis) confirmed expression of complex-type glycoconjugates by plasma membrane and cytoplasmic components of the 3327-H tumour but only by cytoplasmic determinants within 3327 MAT LyLu variant tumour-cells. The only other oligosaccharide freely expressed by either tumour-subline was (GlcNAc beta 1----4GlcNAc beta 1----4-)n, recognised by WGA (Triticum vulgaris). Prior to neuraminidase digestion, PNA (Arachis hypogaea) (which identifies Type I oligosaccharides: Gal beta 1----3GalNAc-) bound to pseudoluminal membranes of the 3327-H tumour. However, ECG (Erythrina cristagalli) (which identifies type II oligosaccharides: Gal beta 1----4GlcNAc-) did not bind to this tumour. Unmasked Type I (Gal beta 1----3GalNAc-) and Type II (Gal beta 1----4GlcNAc-) oligosaccharides were not identified in the MAT-LyLu variant. After neuraminidase digestion, PNA-binding was identified along pseudoluminal plasma membranes within 3327-H tumours but only within the cytoplasm of 3327-MAT LyLu primary and metastatic tumour cells. Following neuraminidase digestion, ECG-binding was observed along pseudoluminal plasma membranes of 3327-H tumours and heterogeneously within the cytoplasm of primary, but not metastatic 3327-MAT LyLu tumours. Terminal alpha/beta GalNAc- residues recognised by SBA (Glycine max) were not freely expressed by either subline. These structures were readily detected along luminal membranes of 3327-H cells and weakly detected within the cytoplasm of primary but not metastatic MAT 3327-LyLu tumour cells following neuraminidase digestion. Fucosylated Type II structures Fuc alpha 1----2Gal(GalNAc)-), recognised by UEA-1 (Ulex europaeus-1) and GalNAc alpha 1----3GalNAc- structures recognised by DBF (Dolichos biflorus) were not identified as a component of either tumour subline. The different patterns of oligosaccharide expression, identified by lectin-binding, clearly differentiated between the two tumour sublines and distinguished them from normal prostatic epithelium. The Dunning 3327 rat prostatic cancer sublines offer a useful model with which to examine the relationship between cell-surface oligosaccharide structures and phenotypic variants within a defined tumour-cell population.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of oligosaccharide determinants expressed by prostatic glandular epithelium of the normal adult rat

Normal prostates from Copenhagen/Fischer F1 hybrid rats were removed at 14 month of age. After routine formalin fixation and paraffin embedding, the expression of seven oligosaccharide structures by prostatic epithelial cells was assessed by an examination of lectin binding sites before and after neuraminidase digestion. Con-A bound to plasma membranes as well as the cytoplasm of all cells, thus confirming the presence of complex-type glycoconjugates. However, only two other oligosaccharides, apart from Con-A, were freely expressed on epithelial luminal plasma membranes. These were the Type I structure (Gal beta 1----3GalNAc-) identified by PNA-binding and (GlcNAc beta 1----4GlcNAc beta 1----4-)n identified by WGA. PNA, WGA, UEA-1 and SBA bound to the cytoplasm of almost all epithelial cells, although their intracellular distribution was not identical. DBF binding was not identified. ECG bound to only a very few cells and then only after digestion with neuraminidase when it was localised to the cytoplasm. Following removal of sialic acid groups by neuraminidase digestion, PNA-binding became more prominent, SBA-binding appeared localized to paranuclear intracellular vesicles and WGA binding sites were abolished. This study has now characterized the major oligosaccharide determinants expressed by rat normal prostatic epithelial cells and provides a baseline against which alterations occurring during ontogenesis and oncogenesis may be compared.

Interactions of concanavalin A with asparagine-linked glycopeptides. Structure/activity relationships of the binding and precipitation of oligomannose and bisected hybrid-type glycopeptides with concanavalin A

We have recently demonstrated that certain oligomannose and bisected hybrid-type glycopeptides are bivalent for concanavalin A (ConA) binding and that they can precipitate the lectin [Bhattacharyya, L., Ceccarini, C., Lorenzoni, P & Brewer, C. F. (1987) J. Biol. Chem. 262, 1288-1293]. Two protein-binding sites on each glycopeptide were identified: one on the alpha(1-6) arm of the core beta-mannose residue which binds with high affinity (primary site); the other on the alpha(1-3) arm of the core beta-mannose residue which binds with lower affinity (secondary site). In the present study, we have investigated the relationship between the structures of the primary sites of oligomannose-type glycopeptides and their affinities for ConA. Two mechanisms of binding at the primary sites of oligomannose-type glycopeptides have been identified which account for the 3000-fold increase in affinity of a Man9 glycopeptide relative to that of methyl alpha-D-mannopyranoside. Changes in the structures and affinities of both the primary and secondary sites are observed to influence the precipitation activities of the glycopeptides. These findings have important consequences for the specificity of ConA binding in solutions containing mixtures of the carbohydrates.

Binding and precipitating activities of Erythrina lectins with complex type carbohydrates and synthetic cluster glycosides. A comparative study of the lectins from E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica

Erythrina lectins possess similar structural and carbohydrate binding properties. Recently, tri- and tetra-antennary complex type carbohydrates with non-reducing terminal galactose residues have been shown to be precipitated as tri- and tetravalent ligands, respectively, with certain Erythrina lectins [Bhattacharyya L, Haraldsson M, Brewer CF (1988) Biochemistry 27:1034-41]. The present work describes a comparative study of the binding and precipitating activities of four Erythrina lectins, viz., E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica, with multi-antennary complex type carbohydrates and synthetic cluster glycosides. The results show that though their binding affinities are very similar, the Erythrina lectins show large differences in their precipitating activities with the carbohydrates. The results also indicate significant dependence of the precipitating activities of the lectins on the core structure of the carbohydrates. These findings provide a new dimension to the structure-activity relationship of the lectins and their interactions with asparagine-linked carbohydrates.

Formation of homogeneous cross-linked lattices between oligomannose type glycopeptides and concanavalin A

Certain oligomannose type glycopeptides have previously been shown to be bivalent for binding to concanavalin A, and to give quantitative precipitation profiles with the protein that consist of single peaks which correspond to the binding stoichiometry of glycopeptide to protein monomer (1:2) (Bhattacharyya, L., Ceccarini, C., Lorenzoni, P., and Brewer, C.F. (1987) J. Biol. Chem. 262, 1288-1293). In the present study, equimolar mixtures of two oligomannose type glycopeptides, a Man-6 and a Man-9 glycopeptide, gives a quantitative precipitation profile which shows two protein peaks. Each glycopeptide was radiolabelled with 3H or 14C, and the the precipitation profiles of the individual glycopeptides in the mixture determined. The results show that the radioactivity profile of the Man-6 glycopeptide corresponds to the first protein peak, while the radioactivity profile of the Man-9 glycopeptide corresponds to the second protein peak. The results indicate that each glycopeptide forms a unique homogeneous cross-linked lattice with the lectin which excludes the lattice of the other glycopeptide.

Binding and precipitation of lectins from Erythrina indica and Ricinus communis (agglutinin I) with synthetic cluster glycosides

We recently reported that tri- and tetraantennary complex type oligosaccharides with nonreducing terminal galactose residues and the triantennary asialofetuin glycopeptide can bind and precipitate certain galactose specific lectins (L. Bhattacharyya, and C.F. Brewer (1986) Biochem. Biophys. Res. Commun. 141, 963-967; L. Bhattacharyya, M. Haraldsson, and C.F. Brewer (1988) Biochemistry 27, 1034-1041). The present study investigates the binding interactions of two of these lectins, those from Erythrina indica and Ricinus communis (Agglutinin I), with mono-, bi-, and triantennary synthetic cluster glycosides, which have little structural resemblance to complex type oligosaccharides other than they possess nonreducing terminal galactose residues (R.T. Lee, P. Lin, and Y.C. Lee (1984) Biochemistry 23, 4255-4261). The enhanced affinities of the bi- and triantennary glycosides relative to the monoantennary glycoside for the two lectins are consistent with an increase in the probability of binding due to multiple binding residues in the multiantennary glycosides. The triantennary glycoside is capable of precipitating the two lectins, and quantitative precipitation data indicate that it is a trivalent ligand. The results show that the binding and precipitation activities of complex type oligosaccharides with these lectins is due solely to the presence of multiple terminal galactose residues and not to the overall structures of the oligosaccharides.