Characterization of the carbohydrate binding specificity of the leukoagglutinating lectin from Maackia amurensis. Comparison with other sialic acid-specific lectins

Group B Streptococcus and Streptococcus suis capsular polysaccharides induce chemokine production by dendritic cells via Toll-like receptor 2- and MyD88-dependent and -independent pathways

Streptococcus agalactiae (also known as group B Streptococcus [GBS]) and Streptococcus suis are encapsulated streptococci causing severe septicemia and meningitis. Bacterial capsular polysaccharides (CPSs) are poorly immunogenic, but anti-CPS antibodies are essential to the host defense against encapsulated bacteria. The mechanisms underlying anti-CPS antibody responses are not fully elucidated, but the biochemistry of CPSs, particularly the presence of sialic acid, may have an immunosuppressive effect. We investigated the ability of highly purified S. suis and GBS native (sialylated) CPSs to activate dendritic cells (DCs), which are crucial actors in the initiation of humoral immunity. The influence of CPS biochemistry was studied using CPSs extracted from different serotypes within these two streptococcal species, as well as desialylated CPSs. No interleukin-1β (IL-1β), IL-6, IL-12p70, tumor necrosis factor alpha (TNF-α), or IL-10 production was observed in S. suis or GBS CPS-stimulated DCs. Moreover, these CPSs exerted immunosuppressive effects on DC activation, as a diminution of gamma interferon (IFN-γ)-induced B cell-activating factor of the tumor necrosis factor family (BAFF) expression was observed in CPS-pretreated cells. However, S. suis and GBS CPSs induced significant production of CCL3, via partially Toll-like receptor 2 (TLR2)- and myeloid differentiation factor 88 (MyD88)-dependent pathways, and CCL2, via TLR-independent mechanisms. No major influence of CPS biochemistry was observed on the capacity to induce chemokine production by DCs, indicating that DCs respond to these CPSs in a patterned way rather than a structure-dedicated manner.

A simple method for assessment of human anti-Neu5Gc antibodies applied to Kawasaki disease

N-Glycolylneuraminic acid (Neu5Gc) is an immunogenic sugar of dietary origin that metabolically incorporates into diverse native glycoconjugates in humans. Anti-Neu5Gc antibodies are detected in all human sera, though with variable levels and epitope-recognition profiles. These antibodies likely play a role in several inflammation-mediated pathologies including cardiovascular diseases and cancer. In cancer, they have dualistic and opposing roles, either stimulating or repressing disease, as a function of their dose, and some of these antibodies serve as carcinoma biomarkers. Thus, anti-Neu5Gc antibodies may signify risk of inflammation-mediated diseases, and changes in their levels could potentially be used to monitor disease progression and/or response to therapy. Currently, it is difficult to determine levels of anti-Neu5Gc antibodies in individual human samples because these antibodies recognize multiple Neu5Gc-epitopes. Here we describe a simple and specific method for detection and overall estimation of human anti-Neu5Gc antibodies. We exploit the difference between two mouse models that differ only by Neu5Gc-presence (wild-type) or Neu5Gc-absence (Cmah^−/− knockout). We characterize mouse serum from both strains by HPLC, lectin and mass-spectrometry analysis and show the target Neu5Gc-epitopes. We then use Cmah^−/− knockout sera to inhibit all non-Neu5Gc-reactivity followed by binding to wild-type sera to detect overall anti-Neu5Gc response in a single assay. We applied this methodology to characterize and quantify anti-Neu5Gc IgG and IgA in sera of patients with Kawasaki disease (KD) at various stages compared to controls. KD is an acute childhood febrile disease characterized by inflammation of coronary arteries that untreated may lead to coronary artery aneurysms with risk of thrombosis and myocardial infarction. This estimated response is comparable to the average of detailed anti-Neu5Gc IgG profile analyzed by a sialoglycan microarray. Both assays revealed an elevated response in acute KD patients with normal coronaries compared to patients with aneurysm or dilated coronaries. Implications of these findings are discussed.

Lectin microarrays: concept, principle and applications

The lectin microarray is a novel platform for glycan analysis, having emerged only in recent years. Unlike other conventional methods, e.g., liquid chromatography and mass spectrometry, it enables rapid and high-sensitivity profiling of complex glycan features without the need for liberation of glycans. Target samples include an extensive range of glycoconjugates involved in cells, tissues, body fluids, as well as synthetic glycans and their mimics. Various procedures for rapid differential glycan profiling have been developed for glycan-related biomarkers. Such glycoproteomics targeting allows precise diagnosis of chronic diseases potentially related to cancer. Application of this method to evaluation of various types of stem cells resulted in the discovery of a new pluripotent cell-specific glycan marker. To explore this technology a more fundamental and extensive understanding of lectins is necessary in relation to the structural uniqueness of glycans. In this chapter, the essence of the lectin microarray is described with some focus on an evanescent-field-activated fluorescence detection principle as a system to achieve in situ (i.e., washing free) aqueous-phase observation under equilibrium conditions. The developed lectin microarray system allows even researchers with poor experience in glycan profiling to perform extensive high-throughput analysis targeting various forms of glycans and even cells.

Molecular recognition of complex-type biantennary N-glycans by protein receptors: a three-dimensional view on epitope selection by NMR

The current surge in defining glycobiomarkers by applying lectins rekindles interest in definition of the sugar-binding sites of lectins at high resolution. Natural complex-type N-glycans can present more than one potential binding motif, posing the question of the actual mode of interaction when interpreting, for example, lectin array data. By strategically combining N-glycan preparation with saturation-transfer difference NMR and modeling, we illustrate that epitope recognition depends on the structural context of both the sugar and the lectin (here, wheat germ agglutinin and a single hevein domain) and cannot always be predicted from simplified model systems studied in the solid state. We also monitor branch-end substitutions by this strategy and describe a three-dimensional structure that accounts for the accommodation of the α2,6-sialylated terminus of a biantennary N-glycan by viscumin. In addition, we provide a structural explanation for the role of terminal α2,6-sialylation in precluding the interaction of natural N-glycans with lectin from Maackia amurensis . The approach described is thus capable of pinpointing lectin-binding motifs in natural N-glycans and providing detailed structural explanations for lectin selectivity.

Lectin-based analysis of fucose and sialic acid expressions on human amniotic IgA during normal pregnancy

The sugar moiety of IgA is known to provide a link between the innate and adaptive immune systems. Terminally located glycotopes on IgA are potential ligands engaged in the interactions which may modulate the biological activities of IgA. In the present work the expressions of Maackia amurensis (MAA), Sambucus nigra (SNA), Lens culinaris (LCA), Tetragonolobus purpureus (LTA), and Ulex europaeus (UEA) reactive glycotopes on maternal plasma and amniotic IgA were evaluated in relation to the progression of a normal human pregnancy, from the 2nd trimester, throughout the 3rd trimester, perinatal period, post-date pregnancy and delivery, by lectin-IgA-ELISA, using specific biotinylated lectins. The amniotic and maternal plasma IgA concentrations and a degree of SNA and LCA reactivity of maternal plasma IgA were almost unaltered during the normal pregnancy. The amniotic IgA from the 2nd trimester was decorated by MAA-, SNA-reactive and LCA-, LTA-, and UEA-reactive glycotopes. At the turn of the 2nd and 3rd trimesters the expression of MAA-, SNA-, LTA-, and UEA-reactive glycotopes, except for LCA-reactive, increased and remained almost at unaltered levels throughout the perinatal period and delivery. However, in the post-date pregnancy the expression of LCA-, LTA-, and UEA-reactive and SNA-reactive glycotopes were significantly higher. The unique fucosylated and sialylated glycovariants of amniotic IgA associated with the progression of the normal pregnancy may illustrate a general importance of carbohydrate-lectin receptor interactions in the control and modulation of biological events to ensuring homeostasis during pregnancy, protection and well-being of fetus.

Detection of glycomic alterations induced by overexpression of p-glycoprotein on the surfaces of L1210 cells using sialic acid binding lectins

P-glycoprotein (P-gp) overexpression is the most frequently observed cause of multidrug resistance in neoplastic cells. In our experiments, P-gp was expressed in L1210 mice leukemia cells (S cells) by selection with vincristine (R cells) or transfection with the gene encoding human P-gp (T cells). Remodeling of cell surface sugars is associated with P-gp expression in L1210 cells as a secondary cellular response. In this study, we monitored the alteration of cell surface saccharides by Sambucus nigra agglutinin (SNA), wheat germ agglutinin (WGA) and Maackia amurensis agglutinin (MAA). Sialic acid is predominantly linked to the surface of S, R and T cells via α-2,6 branched sugars that tightly bind SNA. The presence of sialic acid linked to the cell surface via α-2,3 branched sugars was negligible, and the binding of MAA (recognizing this branch) was much less pronounced than SNA. WGA induced greater cell death than SNA, which was bound to the cell surface and agglutinated all three L1210 cell-variants more effectively than WGA. Thus, the ability of lectins to induce cell death did not correlate with their binding efficiency and agglutination potency. Compared to S cells, P-gp positive R and T cells contain a higher amount of N-acetyl-glucosamine on their cell surface, which is associated with improved WGA binding. Both P-gp positive variants of L1210 cells are strongly resistant to vincristine as P-gp prototypical drug. This resistance could not be altered by liberalization of terminal sialyl residues from the cell surface by sialidase.

Hypomorphic sialidase expression decreases serum cholesterol by downregulation of VLDL production in mice

Lipoprotein metabolism is an important contributing factor in the development and progression of atherosclerosis. Plasma lipoproteins and their receptors are heavily glycosylated and sialylated, and levels of sialic acids modulate their biological functions. Sialylation is controlled by the activities of sialyltranferases and sialidases. To address the impact of sialidase (neu1) activity on lipoprotein metabolism, we have generated a mouse model with a hypomorphic neu1 allele (B6.SM) that displays reduced sialidase expression and sialidase activity. The objectives of this study are to determine the impact of sialidase on the rate of hepatic lipoprotein secretion and lipoprotein uptake. Our results indicate that hepatic levels of cholesterol and triglycerides are significantly higher in B6.SM mice compared with C57Bl/6 mice; however, VLDL-triglyceride production rate is lower. In addition, B6.SM mice show significantly lower levels of hepatic microsomal triglyceride transfer protein (MTP) and active sterol-regulatory element binding protein (SREBP)-2 but higher levels of diglyceride acyltransferase (DGAT)2; these are all indicative of increased hepatic lipid storage. Rescue of sialidase activity in hypomorphic sialidase mice using helper-dependent adenovirus resulted in increased VLDL production and an increase in MTP levels. Furthermore, hypomorphic sialidase expression results in stabilization of hepatic LDL receptor (LDLR) protein expression, which enhances LDL uptake. These findings provide novel evidence for a central role of sialidase in the cross talk between the uptake and production of lipoproteins.

Targeting the glycoproteome

Despite numerous original publications describing the structural complexity of N- and O-linked glycans on glycoproteins, only very few answer the basic question of which particular glycans are linked to which amino acid residues along the polypeptide chain. Such structural information is of fundamental importance for understanding the biological roles of complex glycosylations as well as deciphering their non-template driven biosynthesis. This review focuses on presenting and commenting on recent strategies, specifically aimed at identifying the glycoproteome of cultured cells and biological samples, using targeted and global enrichment procedures and utilizing the high resolution power, high through-put capacity and complementary fragmentation techniques of tandem mass spectrometry. The goal is to give an update of this emerging field of protein and glyco-sciences and suggest routes to bridge the data gap between the two aspects of glycoprotein characteristics, i.e. glycan structures and their attachment sites.

Histochemical identification of sialylated glycans in Xenopus laevis testis

Carbohydrate chains of glycoprotein and glycosphingolipids are highly diverse molecules involved in many cell functions, including cell recognition, adhesion and signalling. Sialylated glycans are of special interest because the terminal position of sialic acid (NeuAc) in glycans linked by different ways to subterminal monosaccharides has been shown to be involved in several biological processes, as occurs with gangliosides, which have been reported as being essential in spermatogenesis in mammals. Some glycan-binding proteins, the lectins, which specifically recognize glycan sequences, have been extensively used to characterize tissue and cell carbohydrates by means of cytochemical techniques. The aim of the present work was to determine the presence of NeuAc by means of histochemical techniques in the testis of Xenopus laevis, an animal model widely used in cell and molecular biology research. However, considering that some NeuAc-binding lectins are capable of binding to N-acetylglucosamine (GlcNAc), other GlcNAc-binding lectins were also assayed. The results showed that NeuAc is mainly expressed in the interstitium, and only a weak labelling in the male germ cells was observed. Most NeuAc was located in O-linked oligosaccharides, but some masked NeuAc in N-glycans were identified in primary and secondary spermatogonia and spermatocytes. By contrast, GlcNAc was widely expressed in all germ cell types. Deglycosylative pre-treatments suggest that both N- and O-glycans and/or glycolipids could be responsible for this labelling. In addition, GlcNAc in O-linked oligosaccharides has been identified in spermatogonial cells. The acrosome of spermatids was always negative. Variations of glycan expression have been found in different cell types, suggesting that glycosylation is modified during spermatogenetic development.

Deficits in sialylation impair podocyte maturation

The role of sialylation in kidney biology is not fully understood. The synthesis of sialoglycoconjugates, which form the outermost structures of animal cells, requires CMP-sialic acid, which is a product of the nuclear enzyme CMAS. We used a knock-in strategy to create a mouse with point mutations in the canonical nuclear localization signal of CMAS, which relocated the enzyme to the cytoplasm of transfected cells without affecting its activity. Although insufficient to prevent nuclear entry in mice, the mutation led to a drastically reduced concentration of nuclear-expressed enzyme. Mice homozygous for the mutation died from kidney failure within 72 hours after birth. The Cmas(nls) mouse exhibited podocyte foot process effacement, absence of slit diaphragms, and massive proteinuria, recapitulating features of nephrin-knockout mice and of patients with Finnish-type congenital nephrotic syndrome. Although the Cmas(nls) mouse displayed normal sialylation in all organs including kidney, a critical shortage of CMP-sialic acid prevented sialylation of nephrin and podocalyxin in the maturing podocyte where it is required during the formation of foot processes. Accordingly, the sialylation defects progressed with time and paralleled the morphologic changes. In summary, sialylation is critical during the development of the glomerular filtration barrier and required for the proper function of nephrin. Whether altered sialylation impairs nephrin function in human disease requires further study.

Histochemical analyses of anti-microbial substances in canine perianal skin with special reference to glandular structures

Circumanal glands are prominent features of the canine perianal skin, which are often located near to the sebaceous glands and apocrine glands. As the functional relevance of circumanal glands is yet unknown, we studied the localisation of sialic acids and anti-microbial substances (lysozyme, immunoglobulin A, lactoferrin, β-defensin) in these glandular structures by lectin histochemistry and immunohistochemistry. The glands exhibited a number of sialic acids that were linked to α2-6Gal/GalNAc and α2-3Galβ1-4GlcNAc. Additionally, lysozyme, lactoferrin and β-defensin could be demonstrated in the three types of skin glands, whereas IgA was only detectable in the apocrine glands. The results of the study suggest the specific significance of the circumanal glands. Independent of a certain endocrine role, their products may mainly function as protective agents to preserve the integrity of the anal region, considering that sialic acids and anti-microbial substances are important in defence mechanisms.

Glycosylation of prostate specific antigen and its potential diagnostic applications

Prostate specific antigen (PSA) assays are widely used for early detection of prostate cancer. However, those analyses are associated with considerable sensitivity and specificity problems. Several approaches have been developed to tackle this issue. PSA is a glycoprotein, which is primarily produced by the prostatic epithelial cells. Aberrant glycosylation modification of proteins is a fundamental characteristic of tumorigenesis. Study of PSA glycoforms offers interesting diagnostic perspectives. Modern technology allows us to analyze PSA glycoforms in a variety of clinical samples (serum or plasma, urine, seminal fluid, tissue). A number of novel techniques, such as lectin-based detection methods, mass spectrometry, 2-dimensional electrophoresis and capillary electrophoresis have been developed to analyze PSA glycosylation. This article reviews the technical and diagnostic aspects of PSA glycoforms.

Colonic carcinogenesis along different genetic routes: glycophenotyping of tumor cases separated by microsatellite instability/stability

Different genetic routes account for colonic carcinogenesis. However, when analyzing colon cancer specimens, separation into different groups based on genetic alterations is commonly not performed. Thus, we here initiate the comparative phenotyping considering microsatellite instability/stability for clinical specimens. The focus is given to glycan epitopes, expression of which is known to be modulated by signal-transducing proteins that act as key regulators of normal colon epithelial growth and differentiation. In addition to six plant lectins used as sensors, the presence of two adhesion/growth-regulatory galectins is studied. Overall, a considerable level of intra- and interindividual heterogeneity is revealed. Alterations in the proportion of stained cells between tumor-adjacent and malignant epithelia concerned plant lectins, which bind substituted N-glycan cores, α2,6-sialylated branch ends, core 1 O-glycans and N-acetylgalactosamine. A tendency for changes was noted between microsatellite-unstable and microsatellite-stable cases for core substitution (bisected N-glycan, presence of β1,6-branching) and status of α2,6-sialylation. Statistical significance was reached for presence of galectin-3, found to be elevated in microsatellite-stable compared to microsatellite-unstable tumors. These results emphasize the potential of distinct signaling pathways to regulate certain aspects of the glycophenotype in vivo and thus delineate a perspective to discern functionally relevant deviations in expression of endogenous lectins and their counter-receptors.

Distribution patterns of influenza virus receptors and viral attachment patterns in the respiratory and intestinal tracts of seven avian species

This study assessed the presence of sialic acid α-2,3 and α-2,6 linked glycan receptors in seven avian species. The respiratory and intestinal tracts of the chicken, common quail, red-legged partridge, turkey, golden pheasant, ostrich, and mallard were tested by means of lectin histochemistry, using the lectins Maackia amurensis agglutinin II and Sambucus nigra agglutinin, which show affinity for α-2,3 and α-2,6 receptors, respectively. Additionally, the pattern of virus attachment (PVA) was evaluated with virus histochemistry, using an avian-origin H4N5 virus and a human-origin seasonal H1N1 virus. There was a great variation of receptor distribution among the tissues and avian species studied. Both α-2,3 and α-2,6 receptors were present in the respiratory and intestinal tracts of the chicken, common quail, red-legged partridge, turkey, and golden pheasant. In ostriches, the expression of the receptor was basically restricted to α-2,3 in both the respiratory and intestinal tracts and in mallards the α-2,6 receptors were absent from the intestinal tract. The results obtained with the lectin histochemistry were, in general, in agreement with the PVA. The differential expression and distribution of α-2,3 and α-2,6 receptors among various avian species might reflect a potentially decisive factor in the emergence of new viral strains.

Terminal sialic acids are an important determinant of pulmonary endothelial barrier integrity

The surface of vascular endothelium bears a glycocalyx comprised, in part, of a complex mixture of oligosaccharide chains attached to cell-surface proteins and membrane lipids. Importantly, understanding of the structure and function of the endothelial glycocalyx is poorly understood. Preliminary studies have demonstrated structural differences in the glycocalyx of pulmonary artery endothelial cells compared with pulmonary microvascular endothelial cells. Herein we begin to probe in more detail structural and functional attributes of endothelial cell-surface carbohydrates. In this study we focus on the expression and function of sialic acids in pulmonary endothelium. We observed that, although pulmonary microvascular endothelial cells express similar amounts of total sialic acids as pulmonary artery endothelial cells, the nature of the sialic acid linkages differs between the two cell types such that pulmonary artery endothelial cells express both α(2,3)- and α(2,6)-linked sialic acids on the surface (i.e., surficially), whereas microvascular endothelial cells principally express α(2,3)-linked sialic acids. To determine whether sialic acids play a role in endothelial barrier function, cells were treated with neuraminidases to hydrolyze sialic acid moieties. Disruption of cell-cell and cell-matrix adhesions was observed following neuraminidase treatment, suggesting that terminal sialic acids promote endothelial barrier integrity. When we measured transendothelial resistance, differential responses of pulmonary artery and microvascular endothelial cells to neuraminidase from Clostridium perfringens suggest that the molecular architecture of the sialic acid glycomes differs between these two cell types. Collectively our observations reveal critical structural and functional differences of terminally linked sialic acids on the pulmonary endothelium.

CHO glycosylation mutants as potential host cells to produce therapeutic proteins with enhanced efficacy

CHO glycosylation mutants, pioneered by Stanley and co-workers, have proven to be valuable tools in glycobiology and biopharmaceutical research. Here we aim to provide a summary of our efforts to isolate industrially applicable CHO glycosylation mutants, termed CHO-gmt cells, using cytotoxic lectins and zinc-finger nuclease technology. The genetic defects in the glycosylation machinery in these cells lead to the production of recombinant glycoproteins with consistent and unique glycan structures. In addition, these mutant cells can be easily adapted to serum-free medium in suspension cultures, the condition used by the biotech industry for large-scale production of recombinant therapeutics. In light of the critical impact of glycosylation on biopharmaceutical performances, namely, safety and efficacy, the CHO-gmt lines have enormous potential in producing glycoprotein therapeutics with optimal glycosylation profiles, thus, representing a panel of ideal host cell lines for producing recombinant biopharmaceuticals with improved safety profiles and enhanced efficacy.

Novel O-linked glycans containing 6'-sulfo-Gal/GalNAc of MUC1 secreted from human breast cancer YMB-S cells: possible carbohydrate epitopes of KL-6(MUC1) monoclonal antibody

Human serum Krebs von den Lugen-6 (KL-6) antigen is a MUC1 glycoprotein (KL-6/MUC1) recognized by anti-KL-6 monoclonal antibody (KL-6/mAb) and has been utilized as a diagnostic marker for interstitial pneumonia. KL-6/mAb is thought to recognize the specific glycopeptides sequence of MUC1, but the precise glycan structure of the epitope is unclear. In this study, we determined the carbohydrate structures of KL-6/MUC1 to search the carbohydrate epitopes for KL-6/mAb. KL-6/MUC1 was purified from the culture medium of human breast cancer YMB-S cells by KL-6/mAb-affinity chromatography; the O-linked glycan structures were determined in combination with paper electrophoresis, several lectin column chromatographies, sialidase digestion and methanolysis. KL-6/MUC1 contained core 1 and extended core 1 glycans modified with one or two sialic acid/sulfate residues. Based on these structures, several synthetic glycans binding to anti-KL-6/mAb were compared with one another by surface plasmon resonance. Sequentially, related radiolabeled oligosaccharides were enzymatically synthesized and analyzed for binding to a KL-6/mAb-conjugated affinity column. 3'-sialylated, 6'-sulfated LNnT [Neu5Acα2-3(SO(3)(-)-6)Galβ1-4GlcNAcβ1-3Galβ1-4Glc], 3'-sialylated, 6-sulfated core 1 [Neu5Acα2-3Galβ1-3(SO(3)(-)-6)GalNAc] and disulfated core 1 SO(3)(-)-3Galβ1-3(SO(3)(-)-6)GalNAc exhibited substantial affinity for KL-6/mAb, and 3'-sulfated core 1 derivatives [SO(3)(-)-3Galβ1-3(±Neu5Acα2-6)GalNAc] and 3'-sialylated core 1 weakly interacted with KL-6/mAb. These results indicated that the possible carbohydrate epitopes of KL-6/mAb involve not only 3'-sialylated core 1 but also novel core 1 and extended core 1 with sulfate and sialic acid residues. Epitope expressing changes with suppression or over-expression of the Gal6ST (Gal 6-O-sulfotransferase) gene, suggesting that Gal6ST is involved in the biosynthesis of the unique epitopes of KL-6/mAb.

Avian influenza viruses infect primary human bronchial epithelial cells unconstrained by sialic acid α2,3 residues

Avian influenza viruses (AIV) are an important emerging threat to public health. It is thought that sialic acid (sia) receptors are barriers in cross-species transmission where the binding preferences of AIV and human influenza viruses are sias α2,3 versus α2,6, respectively. In this study, we show that a normal fully differentiated, primary human bronchial epithelial cell model is readily infected by low pathogenic H5N1, H5N2 and H5N3 AIV, which primarily bind to sia α2,3 moieties, and replicate in these cells independent of specific sias on the cell surface. NHBE cells treated with neuraminidase prior to infection are infected by AIV despite removal of sia α2,3 moieties. Following AIV infection, higher levels of IP-10 and RANTES are secreted compared to human influenza virus infection, indicating differential chemokine expression patterns, a feature that may contribute to differences in disease pathogenesis between avian and human influenza virus infections in humans.

Galectins as tools for glycan mapping in histology: comparison of their binding profiles to the bovine zona pellucida by confocal laser scanning microscopy

Gene divergence has given rise to the galectin family of mammalian lectins. Since selective binding to distinct β-galactosides underlies the known bioactivities of galectins, they could find application in cyto- and histochemistry. The pertinent question on the characteristics of their individual reactivity profiles therefore needs to be answered. Toward this end, comparative studies of a panel of galectins in defined systems are required. We here characterise the staining profiles of seven human lectins as well as five natural derivatives originating from proteolytic truncation and serine phosphorylation and one engineered variant. As test system, bovine germinal vesicle oocytes with their glycoprotein envelope (zona pellucida), which presents bi- to tetraantennary complex-type N-glycans with N-acetyllactosamine repeats and core fucosylation, were processed. Technically, confocal laser scanning microscopy was used, first with plant lectins to map the sialylation status. Hereby, α2,3/6-sialylation was detected in the superficial filamentous meshwork of the zona pellucida, while sialic acid-free glycan chains were found to characterise the main inner part of the compact layer of the zona pellucida. Galectin staining was specific and non-uniform. Significant differences in reactivity were detected for the superficial filamentous meshwork and the compact layer of the zona pellucida between galectins-1 to -4 versus galectins-8 and -9. The typical staining profiles intimate a spatially organised display of N-glycans in the different layers of the zona pellucida, underscoring the potential of galectins as cyto- and histochemical tools. Our results encourage further comparative analysis and research to trace the underlying structural and/or topological properties.

The infection of chicken tracheal epithelial cells with a H6N1 avian influenza virus

Sialic acids (SAs) linked to galactose (Gal) in α2,3- and α2,6-configurations are the receptors for avian and human influenza viruses, respectively. We demonstrate that chicken tracheal ciliated cells express α2,3-linked SA, while goblet cells mainly express α2,6-linked SA. In addition, the plant lectin MAL-II, but not MAA/MAL-I, is bound to the surface of goblet cells, suggesting that SA2,3-linked oligosaccharides with Galβ1–3GalNAc subterminal residues are specifically present on the goblet cells. Moreover, both α2,3- and α2,6-linked SAs are detected on single tracheal basal cells. At a low multiplicity of infection (MOI) avian influenza virus H6N1 is exclusively detected in the ciliated cells, suggesting that the ciliated cell is the major target cell of the H6N1 virus. At a MOI of 1, ciliated, goblet and basal cells are all permissive to the AIV infection. This result clearly elucidates the receptor distribution for the avian influenza virus among chicken tracheal epithelial cells and illustrates a primary cell model for evaluating the cell tropisms of respiratory viruses in poultry.

Interaction and uptake of exosomes by ovarian cancer cells

BACKGROUND

Exosomes consist of membrane vesicles that are secreted by several cell types, including tumors and have been found in biological fluids. Exosomes interact with other cells and may serve as vehicles for the transfer of protein and RNA among cells.

METHODS

SKOV3 exosomes were labelled with carboxyfluorescein diacetate succinimidyl-ester and collected by ultracentrifugation. Uptake of these vesicles, under different conditions, by the same cells from where they originated was monitored by immunofluorescence microscopy and flow cytometry analysis. Lectin analysis was performed to investigate the glycosylation properties of proteins from exosomes and cellular extracts.

RESULTS

In this work, the ovarian carcinoma SKOV3 cell line has been shown to internalize exosomes from the same cells via several endocytic pathways that were strongly inhibited at 4°C, indicating their energy dependence. Partial colocalization with the endosome marker EEA1 and inhibition by chlorpromazine suggested the involvement of clathrin-dependent endocytosis. Furthermore, uptake inhibition in the presence of 5-ethyl-N-isopropyl amiloride, cytochalasin D and methyl-beta-cyclodextrin suggested the involvement of additional endocytic pathways. The uptake required proteins from the exosomes and from the cells since it was inhibited after proteinase K treatments. The exosomes were found to be enriched in specific mannose- and sialic acid-containing glycoproteins. Sialic acid removal caused a small but non-significant increase in uptake. Furthermore, the monosaccharides D-galactose, α-L-fucose, α-D-mannose, D-N-acetylglucosamine and the disaccharide β-lactose reduced exosomes uptake to a comparable extent as the control D-glucose.

CONCLUSIONS

In conclusion, exosomes are internalized by ovarian tumor cells via various endocytic pathways and proteins from exosomes and cells are required for uptake. On the other hand, exosomes are enriched in specific glycoproteins that may constitute exosome markers. This work contributes to the knowledge about the properties and dynamics of exosomes in cancer.

Lectin microarrays for glycomic analysis

Glycomics is the study of comprehensive structural elucidation and characterization of all glycoforms found in nature and their dynamic spatiotemporal changes that are associated with biological processes. Glycocalyx of mammalian cells actively participate in cell-cell, cell-matrix, and cell-pathogen interactions, which impact embryogenesis, growth and development, homeostasis, infection and immunity, signaling, malignancy, and metabolic disorders. Relative to genomics and proteomics, glycomics is just growing out of infancy with great potential in biomedicine for biomarker discovery, diagnosis, and treatment. However, the immense diversity and complexity of glycan structures and their multiple modes of interactions with proteins pose great challenges for development of analytical tools for delineating structure function relationships and understanding glyco-code. Several tools are being developed for glycan profiling based on chromatography, mass spectrometry, glycan microarrays, and glyco-informatics. Lectins, which have long been used in glyco-immunology, printed on a microarray provide a versatile platform for rapid high throughput analysis of glycoforms of biological samples. Herein, we summarize technological advances in lectin microarrays and critically review their impact on glycomics analysis. Challenges remain in terms of expansion to include nonplant derived lectins, standardization for routine clinical use, development of recombinant lectins, and exploration of plant kingdom for discovery of novel lectins.

The sialome--far more than the sum of its parts

The glycome is defined as the glycan repertoire of cells, tissues, and organisms, as found under specified conditions. The vastly diverse glycome is generated by a nontemplate driven biosynthesis, which is indirectly encoded in the genome, and very dynamic. Due to this overwhelming diversity, glycomic analysis must be approached at different hierarchical levels of complexity. In this review five such levels of complexity and the experimental approaches used for analysis at each level are discussed for a subclass of the glycome: the sialome. The sialome, in analogy to the canopy of a forest, covers the cell membrane with diverse array of complex sialylated structures. Sialome complexity includes modification of sialic acid core structure (the leaves and flowers), the linkage to the underlying sugar (the stems), the identity, and arrangement of the underlying glycans (the branches), the structural attributes of the underlying glycans (the trees), and finally, the spatial organization of the sialoglycans in relation to components of the intact cell surface (the forest). Understanding the full complexity of the sialome thus requires combined analyses at multiple levels, that is, the sialome is far more than the sum of its parts.

Decrease of sialic acid residues as an eat-me signal on the surface of apoptotic lymphocytes

The silent clearance of apoptotic cells is essential for cellular homeostasis in multicellular organisms, and several mediators of apoptotic cell recognition have been identified. However, the distinct mechanisms involved are not fully deciphered yet. We analyzed alterations of the glycocalyx on the surfaces of apoptotic cells and its impact for engulfment. After apoptosis induction of lymphocytes, a decrease of α2,6-terminal sialic acids and sialic acids in α2,3-linkage with galactose was observed. Similar changes were to be found on the surface of apoptotic membrane blebs released during early stages of apoptosis, whereas later released blebs showed no impaired, but rather an increased, exposure of sialic acids. We detected an exposure of fucose residues on the surface of apoptotic-cell-derived membrane blebs. Cleavage by neuraminidase of sialic acids, as well as lectin binding to sialic acids on the surfaces, enhanced the engulfment of apoptotic cells and blebs. Interestingly, even viable lymphoblasts were engulfed in an autologous cell system after neuraminidase treatment. Similarly, the engulfment of resting apoptotic lymphocytes was augmented after neuraminidase treatment. However, the engulfment of resting viable lymphocytes was not significantly enhanced after neuraminidase treatment. Our findings support the importance of the glycocalyx, notably the terminal sialic acids, in the regulation of apoptotic cell clearance. Thus, depending on cell type and activation status, changes in surface glycosylation can either directly mediate cellular engulfment or enhance phagocytosis by cooperation with further engulfment signals.

Glycosylation and sialylation of macrophage-derived human apolipoprotein E analyzed by SDS-PAGE and mass spectrometry: evidence for a novel site of glycosylation on Ser290

Apolipoprotein E (apoE) is a 34-kDa glycoprotein secreted from various cells including hepatocytes and macrophages and plays an important role in remnant lipoprotein clearance, immune responses, Alzheimer disease, and atherosclerosis. Cellular apoE and plasma apoE exist as multiple glycosylated and sialylated glycoforms with plasma apoE being less glycosylated/sialylated than cell-derived apoE. Some of the glycan structures on plasma apoE are characterized; however, the more complicated structures on plasma and cellular/secreted apoE remain unidentified. We investigated glycosylation and sialylation of cellular and secreted apoE from primary human macrophages by one- and two-dimensional gel electrophoresis and mass spectrometry. Our results identify eight different glycoforms with (HexNAc)(2)-Hex(2)-(NeuAc)(2) being the most complex glycan detected on Thr(194) in both cellular and secreted apoE. Four additional glycans were identified on apoE(283-299), and using beta-elimination/alkylation by methylamine in vitro, we identified Ser(290) as a novel site of glycan attachment. Comparison of plasma and cellular/secreted apoE from the same donor confirmed that cell-derived apoE is more extensively sialylated than plasma apoE. Given the importance of the C terminus of apoE in regulating apoE solubility, stability, and lipid binding, these results may have important implications for our understanding of apoE biochemistry.

Peptide sugar mimetics prevent HIV type 1 replication in peripheral blood mononuclear cells in the presence of HIV-positive antiserum

Cells of the immune system express a number of receptors that bind carbohydrate ligands. We questioned whether peptide mimetics of these ligands will activate phagocytic cells and thereby enhance an antiviral response. Short peptide sequences were identified by computational modeling of docking to glycan-specific lectins, selected as receptor analogs, and incorporated into quadravalent structures by peptide synthesis. A peptide with the sequence HPSLK bound to several lectins specific for monosaccharides and to lectins specific for Neu5Ac-Gal-containing complex glycans, whereas a longer sequence, NPSHPLSG, bound only lectins specific for the more complex glycans. In cultures of peripheral blood mononuclear cells (PBMCs) these peptides stimulated phagocytosis of opsonized microspheres. The peptides inhibited replication of HIV-1 in PBMC cultures by 20-80% at concentrations between 1 nM and 1 muM but inhibited replication 100% in the presence of diluted HIV-positive antiserum that alone inhibited replication by 30%. HPSLK caused about 50% loss of viability of cells at 1 mM, a concentration 10(6)-fold higher than an effective inhibitory concentration, but no toxicity was observed with NPSHPLSG. These results demonstrated that peptidomimetics of glycan ligands of cellular receptors are effective in activating phagocytosis, which may be a factor in providing complete inhibition of HIV-1 replication in vitro.

Fut2-null mice display an altered glycosylation profile and impaired BabA-mediated Helicobacter pylori adhesion to gastric mucosa

Glycoconjugates expressed on gastric mucosa play a crucial role in host-pathogen interactions. The FUT2 enzyme catalyzes the addition of terminal alpha(1,2)fucose residues, producing the H type 1 structure expressed on the surface of epithelial cells and in mucosal secretions of secretor individuals. Inactivating mutations in the human FUT2 gene are associated with reduced susceptibility to Helicobacter pylori infection. H. pylori infects over half the world's population and causes diverse gastric lesions, from gastritis to gastric cancer. H. pylori adhesion constitutes a crucial step in the establishment of a successful infection. The BabA adhesin binds the Le(b) and H type 1 structures expressed on gastric mucins, while SabA binds to sialylated carbohydrates mediating the adherence to inflamed gastric mucosa. In this study, we have used an animal model of nonsecretors, Fut2-null mice, to characterize the glycosylation profile and evaluate the effect of the observed glycan expression modifications in the process of H. pylori adhesion. We have demonstrated expression of terminal difucosylated glycan structures in C57Bl/6 mice gastric mucosa and that Fut2-null mice showed marked alteration in gastric mucosa glycosylation, characterized by diminished expression of alpha(1,2)fucosylated structures as indicated by lectin and antibody staining and further confirmed by mass spectrometry analysis. This altered glycosylation profile was further confirmed by the absence of Fucalpha(1,2)-dependent binding of calicivirus virus-like particles. Finally, using a panel of H. pylori strains, with different adhesin expression profiles, we have demonstated an impairment of BabA-dependent adhesion of H. pylori to Fut2-null mice gastric mucosa, whereas SabA-mediated binding was not affected.

Terminal monosaccharide screening of synovial immunoglobulins G and A for the early detection of rheumatoid arthritis

The expressions of some terminal glycotopes of synovial immunoglobulins G, A, and M were analysed in relation to rheumatoid arthritis (RA) progression defined according to early and advanced radiological changes in patients' hands. The relative amounts of terminal monosaccharides were determined by lectin-immunoblotting of immunoglobulin preparations using appropriate lectins able to recognize alpha2,6-linked (Sambucus nigra agglutinin) and alpha2,3-linked (Maackia amurensis agglutinin) sialic acid, galactose (Ricinus communis agglutinin I), N-acetylglucosamine (Griffonia simplicifolia agglutinin II) as well as alpha1,6-linked (Aleuria aurantia lectin), alpha1,3-linked (Lotus tetragonolobus agglutinin), and alpha1,2-linked (Ulex europaeus agglutinin) fucose. The results indicate differences between early and advanced RA stages in the terminal sugar exposition of synovial IgG and IgA, but not IgM. The galactose-deficient glycotope with exposed N-acetylglucosamine of the synovial 33.1-kDa IgG fragment appeared exclusively in the early stage of RA. In contrast, this glycotope of intact synovial IgG and IgA was present in both groups, although with higher proportions in advanced RA. The proportions of the sialyl and fucosyl determinants of intact synovial A and G immunoglobulins were clearly lower in the early RA group than in the advanced. The analysis of terminal oligosaccharide exposition in IgG, IgG fragments, and IgA present in the synovial fluid of RA patients might be applicable as a stage-specific marker in the diagnosis and therapy of RA patients.

Fabrication and characterization of a sialoside-based carbohydrate microarray biointerface for protein binding analysis with surface plasmon resonance imaging

Monitoring multiple biological interactions in a multiplexed array format has numerous advantages. However, converting well-developed surface chemistry for spectroscopic measurements to array-based high-throughput screening is not a trivial process and often proves to be the bottleneck in method development. This paper reports the fabrication and characterization of a new carbohydrate microarray with synthetic sialosides for surface plasmon resonance imaging (SPRi) analysis of lectin-carbohydrate interactions. Contact printing of functional sialosides on neutravidin-coated surfaces was carried out and the properties of the resulting elements were characterized by fluorescence microscopy and atomic force microscopy (AFM). Sambucus nigra agglutinin (SNA) was deposited on four different carbohydrate functionalized surfaces and differential binding was analyzed to reveal affinity variation as a function of headgroup sialic acid structures and linking bonds. SPRi studies indicated that this immobilization method could result in high quality arrays with RSD < 5% from array element to array element, superior to the conventional covalent linkage used for protein cholera toxin (CT) in a comparison experiment, which yields nonuniform array elements with RSD > 15%. Multiplexed detection of SNA/biotinylated sialoside interactions on arrays up to 400 elements has been performed with good data correlation, demonstrating the effectiveness of the biotin-neutravidin-based biointerface to control probe orientation for reproducible and efficient protein binding to take place. Additionally, the regeneration of the array surface was demonstrated with a glycine stripping buffer, rendering this interface reusable. This in-depth study of array surface chemistry offers useful insight into experimental conditions that can be optimized for better performance, allowing many different protein-based biointeractions to be monitored in a similar manner.

The repertoire of glycan determinants in the human glycome

The number of glycan determinants that comprise the human glycome is not known. This uncertainty arises from limited knowledge of the total number of distinct glycans and glycan structures in the human glycome, as well as limited information about the glycan determinants recognized by glycan-binding proteins (GBPs), which include lectins, receptors, toxins, microbial adhesins, antibodies, and enzymes. Available evidence indicates that GBP binding sites may accommodate glycan determinants made up of 2 to 6 linear monosaccharides, together with their potential side chains containing other sugars and modifications, such as sulfation, phosphorylation, and acetylation. Glycosaminoglycans, including heparin and heparan sulfate, comprise repeating disaccharide motifs, where a linear sequence of 5 to 6 monosaccharides may be required for recognition. Based on our current knowledge of the composition of the glycome and the size of GBP binding sites, glycoproteins and glycolipids may contain approximately 3000 glycan determinants with an additional approximately 4000 theoretical pentasaccharide sequences in glycosaminoglycans. These numbers provide an achievable target for new chemical and/or enzymatic syntheses, and raise new challenges for defining the total glycome and the determinants recognized by GBPs.

Glycoproteomics for prostate cancer detection: changes in serum PSA glycosylation patterns

Currently, serum prostate-specific antigen (PSA) is used for the early detection of prostate cancer despite its low specificity in the range of 4-10 ng/mL. Because aberrant glycosylation is a fundamental characteristic of tumor genesis, the objective of this study was to investigate whether changes in PSA glycosylation may be used to improve the cancer specificity of PSA. We developed five lectin immunosorbant assays to analyze the glycosylation patterns of PSA in serum. Each assay sandwiches serum PSA between a PSA monoclonal antibody and a biotinylated lectin and then tags the biotin complex using a streptavidin SULFO TAG for electrochemiluminescence detection. Low limits of detection (0.04-1.35 ng/mL), good reproducibility (%CVs < 10%), and direct analysis of PSA glycosylation in sera suggest these assays may have a potential role in improving PSA's cancer specificity. Clinical performance was evaluated in 52 human subjects (26 cancer and 26 noncancer). ROC analysis showed that the total SNA assay (AUC = 0.71) appeared to perform better than percent free PSA (AUC = 0.54) in its diagnostic gray zone between 10 and 20% in a subset of 21 subjects. A separate study of 16 additional subjects showed similar findings.

Compensation of loss of protein function in microsatellite-unstable colon cancer cells (HCT116): a gene-dependent effect on the cell surface glycan profile

Tumors that display a high level of microsatellite instability (MSI-H) accumulate somatic frameshift mutations in several genes. The compensation of this loss of function by transfection represents a suitable approach to tie respective gene deficiency to alterations in cellular characteristics. In view of the emerging significance of cell surface glycans as biochemical signals for presentation/activity of various receptors/integrins and for susceptibility to adhesion/growth-regulatory tissue lectins, we examined the glycophenotype in the MSI-H colon cancer cell line HCT116 for activin type 2 receptor (ACVR2), absent in melanoma 2 (AIM2), and transforming growth factor beta-type 2 receptor (TGFBR2) known to be associated with MSI colorectal carcinogenesis. A panel of probes specific for functional carbohydrate epitopes including human lectins was used to trace changes in cell surface levels, thereby initiating glycan analysis related to MSI. In particular, the presence of core substitutions and branching in N-glycans, the sialylation status of N- and O-glycans, and the presence of Le(a/x)-epitopes were profiled. Transient transfection affected the glycophenotype, depending on the nature of the gene and the probe. The TGFBR2 presence reduced binding of probes specific for a core substitution and increased branch length in N-glycosylation, even reaching a P-value of 0.0016. ACVR2/AIM2 influenced core 1 mucin-type O-glycosylation differentially, upregulation by ACVR2, and downregulation by AIM2. These alterations of cell surface glycosylation by gene products that are not directly associated with the machinery for glycan generation direct attention to pursue analysis of glycosylation in MSI tumor cells on the level of target glycoproteins and open the way for functional studies.

High expression of alpha 2, 3-linked sialic acid residues is associated with the metastatic potential of human gastric cancer

BACKGROUND

Sialic acid, as a terminal saccharide residue on cell surface glycoconjugates, plays an important role in a variety of biological processes. However, the precise nature of the molecules in gastric cancers has not been unveiled nor documented to be of clinical relevance. Herein, we measured the expression of alpha 2, 3-linked sialic acid residues by using a specific lectin as well as the potential of invasion and metastasis of gastric cancer was analyzed.

METHODS

The expression of alpha 2, 3-linked sialic acid residues in 100 cases of gastric cancer samples was evaluated using Maackia amurensis leukoagglutinin (MAL) histochemical staining analysis. The assays of cytochemical staining and flow cytometry were employed to determine the MAL positive cells in the gastric cancer cell lines. The activities of invasion and migration were evaluated using the assays of cell adhesion and transwell chamber.

RESULTS

The staining of MAL in gastric cancer tissues showed that high levels of alpha 2, 3-linked sialic acid residues were closely associated with the invasive depth (P=0.0003) and lymph node metastasis (P=0.0441). In gastric adenocarcinoma cell lines, SGC-7901, the highly metastatic cell line, displayed the most positive reaction with MAL among the selected cell lines. The potential of invasion and migration was confirmed using the assays of adhesion and transwell chamber that SGC-7901 exhibited the high activity of adhesion to extracellular matrix (ECM) and penetration to Matrigel.

CONCLUSION

These results suggested that high level of alpha 2, 3-linked sialic acid residues was associated with metastatic potential of gastric cancer cells.

Glycoprofiling of the Human Salivary Proteome

Glycosylation is important for a number of biological processes and is perhaps the most abundant and complicated of the known post-translational modifications found on proteins. This work combines two-dimensional polyacrylamide gel electrophoresis (2-DE) and lectin blotting to map the salivary glycome, and mass spectrometry to identity the proteins that are associated with the glycome map. A panel of 15 lectins that recognize six sugar-specific categories was used to visualize the type and extent of glycosylation in saliva from two healthy male individuals. Lectin blots were compared to 2-D gels stained either with Sypro Ruby (protein stain) or Pro-Q Emerald 488 (glycoprotein stain). Each lectin shows a distinct pattern, even those belonging to the same sugar-specific category. In addition, the glycosylation profiles generated from the lectin blots show that most of the salivary proteins are glycosylated and that the pattern is more widespread than is demonstrated by the glycoprotein stained gel. Finally, the co-reactivity between two lectins was measured to determine the glycan structures that are most and least often associated with one another along with the population variation of the lectin reactivity for 66 individuals.

The Golgi CMP-sialic acid transporter: A new CHO mutant provides functional insights

A CHO mutant line, MAR-11, was isolated using a cytotoxic lectin, Maackia amurensis agglutinin (MAA). This mutant has decreased levels of cell surface sialic acid relative to both wild-type CHO-K1 and Lec2 mutant CHO cells. The CMP-sialic acid transporter (CMP-SAT) gene in the MAR-11 mutant cell has a C-T mutation that results in a premature stop codon. As a result, MAR-11 cells express a truncated version of CMP-SAT which contains only 100 amino acids rather than the normal CMP-SAT which contains 336 amino acids. Biochemical analyses indicate that recombinant interferon-gamma (IFN-gamma) produced by the mutant cells lack sialic acid. Using MAR-11 as host cells, an EPO/IEF assay for the structure-function study of CMP-SAT was developed. This assay seems more sensitive than previous assays that were used to analyze sialylation in Lec2 cells. Cotransfection of constructs that express CMP-SAT into MAR-11 cells completely converted the recombinant EPO to a sialylation pattern that is similar to the EPO produced by the wild-type CHO cells. Using this assay, we showed that CMP-SAT lacking C-terminal 18 amino acids from the cytosolic tail was able to allow high levels of EPO sialylation. Substitution of the Gly residues with Ile in three different transmembrane domains of CMP-SAT resulted in dramatic decreases in transporter's activity. The CMP-SAT only lost partial activity if the same Gly residues were substituted with Ala, suggesting that the lack of side chain in Gly residues in the transmembrane domains is essential for transport activity.

Surface plasmon resonance study of protein-carbohydrate interactions using biotinylated sialosides

Lectins are carbohydrate binding proteins found in plants, animals, and microorganisms. They serve as important models for understanding protein-carbohydrate interactions at the molecular level. We report here the fabrication of a novel sensing interface of biotinylated sialosides to probe lectin-carbohydrate interactions using surface plasmon resonance spectroscopy (SPR). The attachment of carbohydrates to the surface using biotin-NeutrAvidin interactions and the implementation of an inert hydrophilic hexaethylene glycol spacer (HEG) between the biotin and the carbohydrate result in a well-defined interface, enabling desired orientational flexibility and enhanced access of binding partners. The specificity and sensitivity of lectin binding were characterized using Sambucus nigra agglutinin (SNA) and other lectins including Maackia amurensis lectin (MAL), concanavalin A (Con A), and wheat germ agglutinin (WGA). The results indicate that alpha2,6-linked sialosides exhibit high binding affinity to SNA, while alteration in sialyl linkage and terminal sialic acid structure compromises the affinity by a varied degree. Quantitative analysis yields an equilibrium dissociation constant (KD) of 777 +/- 93 nM for SNA binding to Neu5Ac alpha2,6-LHEB. Transient SPR kinetics confirms the K D value from the equilibrium binding studies. A linear relationship was obtained in the 10-100 microg/mL range with limit of detection of approximately 50 nM. Weak interactions with MAL, Con A, and WGA were also quantified. The control experiment with bovine serum albumin indicates that nonspecific interaction on this surface is insignificant over the concentration range studied. Multiple experiments can be performed on the same substrate using a glycine stripping buffer, which selectively regenerates the surface without damaging the sialoside or the biotin-NeutrAvidin interface. This surface design retains a high degree of native affinity for the carbohydrate motifs, allowing distinction of sialyl linkages and investigation pertaining to the effect of functional group on binding efficiency. It could be easily modified to identify and quantify binding patterns of any low-affinity biologically relevant systems, opening new avenues for probing carbohydrate-protein interactions in real time.