Concanavalin A interactions with asparagine-linked glycopeptides. The mechanisms of binding of oligomannose, bisected hybrid, and complex type carbohydrates

N-glycoproteins in Plant Cell Walls: A Survey

Cell walls are an extracellular compartment specific to plant cells, which are not found in animal cells. Their composition varies between cell types, plant species, and physiological states. They are composed of a great diversity of polymers, i.e., polysaccharides, proteins, and lignins. Cell wall proteins (CWPs) are major players involved in the plasticity of cell walls which support cell growth and differentiation, as well as adaptation to environmental changes. In order to reach the extracellular space, CWPs are transported through the secretory pathway where they may undergo post-translational modifications, including N-glycosylations on the Asn residues in specific motifs (Asn-X-Ser/Thr-X, with X≠Pro). This review aims at providing a survey of the present knowledge related to cell wall N-glycoproteins with (i) an overview of the experimental workflows, (ii) a selection of relevant articles dedicated to N-glycoproteomics, (iii) a description of the diversity of N-glycans, and (iv) a focus on the importance of N-glycans for CWP structure and/or function.

N-Glycans in Xenopus laevis testis characterised by lectin histochemistry

Analysis of glycan chains of glycoconjugates is difficult because of their considerable variety. Despite this, several functional roles for these glycans have been reported. N-Glycans are oligosaccharides linked to asparagine residues of proteins. They are synthesised in the endoplasmic reticulum (ER) in a unique way, and later modified in both the ER and Golgi apparatus, developing different oligosaccharide chains. An essential role for complex N-glycans in mammalian spermatogenesis has been reported. The aim of the present study was to analyse the N-glycans of the Xenopus laevis testis by means of lectin histochemistry. Five lectins were used that specifically recognise mannose-containing and complex glycans, namely Galanthus nivalis agglutinin (GNA) from snowdrops, concanavalin A (Con A) from the Jack bean, Lens culinaris agglutinin (LCA) from lentils and Phaseolus vulgaris erythroagglutinin (PHA-E) and P. vulgaris leukoagglutinin (PHA-L) from the common bean. GNA and Con A labelled the interstitium and most of the germ cell types, whereas LCA and PHA-E showed affinity only for the interstitium. A granular cytoplasmic region was labelled in spermatogonia and spermatocytes by GNA and PHA-L, whereas GNA and LCA labelled a spermatid region that is probably associated with the centriolar basal body of the nascent flagellum. There was no specific labelling in the acrosome. Some unexpected results were found when deglycosylative pretreatments were used: pre-incubation of tissue sections with peptide N glycosidase F, which removes N-linked glycans, reduced or removed labelling with most lectins, as expected. However, after this pretreatment, the intensity of labelling remained or increased for Con A in the follicle (Sertoli) and post-meiotic germ cells. The β-elimination procedure, which removes O-linked glycans, revealed new labelling patterns with GNA, LCA and PHA-L, suggesting that some N-glycans were masked by O-glycans, and thus they became accessible to these lectins only after removal of the O-linked oligosaccharides. The functional role of the glycan chains identified could be related to the role of N-glycans involved in mammalian spermatogenesis reported previously.

Polymer-based photocoupling agent for the efficient immobilization of nanomaterials and small molecules

A highly efficient photocoupling agent, based on perfluorophenylazide (PFPA)-conjugated polyallylamine (PAAm), was developed for the efficient immobilization of polymers, nanoparticles, graphene, and small molecules. The conjugate, PAAm-PFPA, was synthesized, and the percentage of the photoactive moiety, PFPA, can be controlled by the ratio of the two components in the synthesis. By treating epoxy-functionalized wafers with PAAm-PFPA, photoactive surfaces were generated. Compared with the PFPA surface, these polymer-based photocoupling matrix resulted in significantly enhanced immobilization efficiencies, especially for nanomaterials and small molecules. Thus, polystyrene nanoparticles (PS NPs) and alkyl-functionalized silica nanoparticles (SNPs) were successfully immobilized on the PAAm-PFPA surface, resulting in a high material density. Graphene flakes patterned on the PAAm-PFPA surface showed improved feature resolution in addition to a higher material density compared to that of flakes immobilized on the PFPA surface. Furthermore, 2-O-α-D-mannopyranosyl-D-mannopyranose (Man2) immobilized on the PAAm-PFPA surface exhibited significantly enhanced signals when treated with lectin concanavalin A (Con A).

Lectin histochemistry on the dorsal epidermis of the Breton dog

Expression of sugar residues and the nature of oligosaccharide linkage during keratinocyte maturation in the epidermis of the Breton dog were studied with the use of lectin histochemistry. Thirteen lectins were used. Labelling was not observed with GSA I-B4, GSA II, UEA-I, and LTA. The cytoplasm of keratinocytes reacted with PNA, HPA, Con A, and WGA from the basal layer to the granular layer. PNA and Con A showed highest reactivity in the granular cell layer. The cell surface showed increased reactivity with PNA, HPA, and WGA with maturation of keratinocytes. KOH-neuraminidase treatment (KOH-Neu) increased PNA and RCA120 staining during keratinocyte differentiation thus indicating an increase in oligosaccharides terminating with sialic acid-Galbeta(1,3)GalNAc and sialic acid-Galbeta(1,4)GlcNAc, respectively. Labelling of the glycocalyx of basal and spinous keratinocytes with SNA and MAA revealed terminal Neu5acalpha(2,6)Gal/GalNAc and Neu5acalpha(2,3)Galbeta(1,4)GlcNAc. KOH-Neu-DBA showed oligosaccharides terminating with sialic acid-GalNAcalpha(1,3)GalNAc in the spinous and granular layers. A selective glycocalyx labelling of granular keratinocytes was observed with DBA and SBA. Reactions with MAA, PNA, DBA, RCA120, SBA, HPA, and WGA disappeared after the beta-elimination reaction. Our findings indicate that Breton dog epidermis contains more O-linked than N-linked oligosaccharides and confirm that different subpopulations of keratinocytes can be distinguished by lectin histochemistry.

Crystal structure of the lectin from Dioclea grandiflora complexed with core trimannoside of asparagine-linked carbohydrates

The seed lectin from Dioclea grandiflora (DGL) has recently been shown to possess high affinity for 3, 6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranose, the core trimannoside of asparagine-linked carbohydrates, but lower affinity for biantennary complex carbohydrates. In the previous paper, the thermodynamics of DGL binding to deoxy analogs of the core trimannoside and to a biantennary complex carbohydrate were determined by isothermal titration microcalorimetry. The data suggest that DGL recognizes specific hydroxyl groups of the trimannoside similar to that of the jack bean lectin concanavalin A (ConA) (Gupta, D. Dam, T. K., Oscarson, S., and Brewer, C. F. (1997) J. Biol. Chem. 272, 6388-6392). However, the thermodynamics of DGL binding to certain deoxy analogs and to the complex carbohydrate are different from that of ConA. In the present paper, the x-ray crystal structure of DGL complexed to the core trimannoside was determined to a resolution of 2.6 A. The overall structure of the DGL complex is similar to the structure of the ConA-trimannoside complex (Naismith, J. H., and Field, R. A. (1996) J. Biol. Chem. 271, 972-976). The location and conformation of the bound trimannoside as well as its hydrogen-bonding interactions in both complexes are nearly identical. However, differences exist in the location of two loops outside of the respective binding sites containing residues 114-125 and 222-227. The latter residues affect the location of a network of hydrogen-bonded water molecules that interact with the trisaccharide. Differences in the arrangement of ordered water molecules in the binding site and/or protein conformational differences outside of the binding site may account for the differences in the thermodynamics of binding of the two lectins to deoxy analogs of the trimannoside. Molecular modeling studies suggest how DGL discriminates against binding the biantennary complex carbohydrate relative to ConA.

Identification of N- and O-linked oligosaccharides in the human epididymis

The oligosaccharide sequences of glycoconjugates in the human normal epididymis and the nature of linkages were studied with lectin histochemistry. The usual terminal sequences of oligosaccharide side chains in epithelial cell secretions were Neu5Ac2,3Galbeta1,3GalNAc; SO4Galbeta1,3GalNAc; and Galbeta1,4GlcNAc, and they were mainly found in O-linked glycoproteins. The lectin pattern of mitochondria-rich cells differed from that of principal cells.

Characterization of glycoproteins in the epithelial cells of human and other mammalian gallbladder. A review

The mammalian gallbladder mucosa is lined by a simple columnar epithelium. Typical surface epithelial cells (principal cells) contain short microvilli, secretory granules, dense bodies, mitochondria and Golgi apparatus. Dense bodies are thought to be lysosomes. Secretory granules contain mucous glycoproteins which are released to the lumen by exocytosis. Oligosaccharide side chains of mucous glycoproteins may provide a favorable environment for nucleation of cholesterol in gallstone formation; therefore they have been studied during the past decades. Histochemical techniques allow the in situ identification of carbohydrates at both the cellular and subcellular levels. The oligosaccharide chains of principal cell mucous glycoproteins have been studied by classical histochemical techniques (PAS, alcian blue, HID, etc). These techniques indicate that mammalian gallbladder mucous glycoproteins are heavily sulphated, whereas sialic acid residues are scarce. Neutral mucins have not been described in the mammalian gallbladder. Electron microscopic studies have located the oligosaccharide chains in secretory granules and Golgi apparatus. More recently, lectins (molecules which specifically recognize and bind with different saccharides or saccharide sequences) have been applied for the intracellular localization of carbohydrate residues. Lectin histochemistry has detected fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues in mucous granules, Golgi apparatus and apical membrane of human principal cells. Mannose residues were observed only in dense bodies. The combined use of deglycosylation procedures and lectin histochemistry has revealed a variety of terminal sequences in oligosaccharide chains of gallbladder mucous glycoproteins: Neu5Ac(alpha 2-3)Gal(beta 1-3)GalNAc, Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc and Gal(beta 1-4)GlcNAc. This technology also suggested the occurrence of N-linked oligosaccharides in the dense bodies of principal cells. Mucous granules mainly contained mucin-type O-linked oligosaccharides although some N-linked chains have also been detected. Gallstone formation is probably a complex process depending on multiple factors. Mucous glycoproteins are one of the factors involved in this process. Histochemical methods offer an excellent research tool for the characterization of glycoproteins in the epithelial cells of the gallbladder, thus contributing to the elucidation of the pathophysiology of gallstone formation.

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.

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.

Subcellular characterization of glycoproteins in the principal cells of human gallbladder. A lectin cytochemical study

Gallbladder mucus is mainly composed of glycoproteins, which seem to play a critical role in cholesterol nucleation during gallstone formation. The biosynthetic pathway and sequential processing as well as the characterization of the oligosaccharide side-chains of human gallbladder secretory glycoproteins have not been completely defined. The aim of the present study is the subcellular characterization of the glycoproteins in the principal cells of human gallbladder. Principal cells of normal human gallbladder were studied by means of a variety of cytochemical techniques, including lectin histochemistry, enzyme and chemical treatments, immunocytochemistry and lectin-gold technology. Fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues were detected in mucous granules, Golgi apparatus and apical membrane of principal cells. Mannose residues were only observed in dense bodies. Oligosaccharide side-chains of the glycoproteins contained in the biliary mucus are synthesized in the Golgi apparatus of the principal cells of the gallbladder epithelium and are also contained in the mucous granules of these cells. Terminal N-acetylneuraminic acid(alpha 2-3)galactose(beta 1-3)N-acetylgalactosamine, N-acetylneuraminic acid(alpha 2-3)galactose(beta 1-4)N-acetylglucosamine and galactose(beta 1-4)N-acetylglucosamine sequences are contained in the oligosaccharide chains of gallbladder mucus glycoproteins. The dense bodies detected in the cytoplasm of the principal cells contained N-linked glycoproteins. Mucin-type O-linked glycoproteins were the main components of the mucous granules although some N-linked chains were also detected.

Development of concanavalin A-enzyme immunosorbent assay for glycated haptoglobin using polyclonal and monoclonal antibodies

Two-site lectin-haptoglobin-enzyme immunosorbent assay (L-Hp-ELISA), is described. Haptoglobin binding to Concanavalin A, immobilized to polystyrene microtiter plate, was estimated by anti-haptoglobin polyclonal and monoclonal antibodies conjugated with horse-radish peroxidase. The range of haptoglobin binding to Concanavalin A, measured by the L-Hp-ELISA was 25 to 300 ng/ml using polyclonal, and 50 to 600 ng/ml using monoclonal anti-haptoglobin antibodies, respectively.