Structure of the major concanavalin A reactive oligosaccharides of the extracellular matrix component laminin

Galectin-3: A factotum in carcinogenesis bestowing an archery for prevention

Cancer metastasis and therapy resistance are the foremost hurdles in oncology at the moment. This review aims to pinpoint the functional aspects of a unique multifaceted glycosylated molecule in both intracellular and extracellular compartments of a cell namely galectin-3 along with its metastatic potential in different types of cancer. All materials reviewed here were collected through the search engines PubMed, Scopus, and Google scholar. Among the 15 galectins identified, the chimeric gal-3 plays an indispensable role in the differentiation, transformation, and multi-step process of tumor metastasis. It has been implicated in the molecular mechanisms that allow the cancer cells to survive in the intravascular milieu and promote tumor cell extravasation, ultimately leading to metastasis. Gal-3 has also been found to have a pivotal role in immune surveillance and pro-angiogenesis and several studies have pointed out the importance of gal-3 in establishing a resistant phenotype, particularly through the epithelial-mesenchymal transition process. Additionally, some recent findings suggest the use of gal-3 inhibitors in overcoming therapeutic resistance. All these reports suggest that the deregulation of these specific lectins at the cellular level could inhibit cancer progression and metastasis. A more systematic study of glycosylation in clinical samples along with the development of selective gal-3 antagonists inhibiting the activity of these molecules at the cellular level offers an innovative strategy for primary cancer prevention.

Neuronally produced versican V2 renders C-fiber nociceptors IB4 -positive

A subpopulation of nociceptors, the glial cell line-derived neurotrophic factor (GDNF)-dependent, non-peptidergic C-fibers, expresses a cell-surface glycoconjugate that can be selectively labeled with isolectin B4 (IB4 ), a homotetrameric plant lectin from Griffonia simplicifolia. We show that versican is an IB4 -binding molecule in rat dorsal root ganglion neurons. Using reverse transcriptase polymerase chain reaction (RT-PCR), in situ hybridization and immunofluorescence experiments on rat lumbar dorsal root ganglion, we provide the first demonstration that versican is produced by neurons. In addition, by probing Western blots with splice variant-specific antibodies we show that the IB4 -binding versican contains only the glycosaminoglycan alpha domain. Our data support V2 as the versican isoform that renders this subpopulation of nociceptors IB4 -positive (+). A subset of nociceptors, the GDNF-dependent non-peptidergic C-fibers can be characterized by its reactivity for isolectin B4 (IB4), a plant lectin from Griffonia simplicifolia. We have previously demonstrated that versican V2 binds IB4 in a Ca2 + -dependent manner. However, given that versican is thought to be the product of glial cells, it was questionable whether versican V2 can be accountable for the IB4-reactivity of this subset of nociceptors. The results presented here prove - for the first time - a neuronal origin of versican and suggest that versican V2 is the molecule that renders GDNF-dependent non-peptidergic C-fibers IB4-positive.

An N-acetyllactosamine-specific lectin, PFA, isolated from a moth (Phalera flavescens), structurally resembles an invertebrate-type lysozyme

PFA (Phalera flavescens agglutinin) lectin purified from larvae of the lobster moth (P. flavescens) shows a strong binding ability specific to the N-acetyllactosamine (Galβ1-4GlcNAc) site. We determined the genomic and cDNA sequences of the PFA gene, which consists of five exons and spans approximately 5 kb of a genomic region. Surprisingly, the amino acid sequence (149 amino acids) was similar to invertebrate-type lysozymes and related proteins. The predicted tertiary structure of the PFA protein was similar to the lysozymes of clams such as the common orient clam (Meretrix lusoria) and Japanese littleneck (Venerupis philippinarum (Tapes japonica)). The PFA, however, lacks a catalytically essential amino acid, an Asp (D), which is one of the two important amino acids (Glu (E) and D) express the function of lysozyme. As a result, lysozyme activity assays indicated that PFA does not have lysozyme activity. Results suggest that the PFA gene evolved from a lysozyme gene through the loss of lysozyme activity sites and the acquisition of lectin activity during evolution of the genus Phalera.

Comprehensive list of lectins: origins, natures, and carbohydrate specificities

More than 100 years have passed since the first lectin ricin was discovered. Since then, a wide variety of lectins (lect means "select" in Latin) have been isolated from plants, animals, fungi, bacteria, as well as viruses, and their structures and properties have been characterized. At present, as many as 48 protein scaffolds have been identified as functional lectins from the viewpoint of three-dimensional structures as described in this chapter. In this chapter, representative 53 lectins are selected, and their major properties that include hemagglutinating activity, mitogen activity, blood group specificity, molecular weight, metal requirement, and sugar specificities are summarized as a comprehensive table. The list will provide a practically useful, comprehensive list for not only experienced lectin users but also many other non-expert researchers, who are not familiar to lectins and, therefore, have no access to advanced lectin biotechnologies described in other chapters.

Multiplex profiling of glycoproteins using a novel bead-based lectin array

Lectin array is becoming important in profiling targeted glycan/glycoprotein, but weak interaction between lectin and glycan causes low sensitivity of the approach. This study aims to develop a bead-based lectin array for improving the sensitivity of glycosylation profiling. Lectins are chemically coupled to fluorescent dye coated microbeads, and glycan-lectin recognition is carried out three dimensionally. The performance of this platform was evaluated, and the LOD of lectin Ricinus communis agglutinin 120 (RCA120) was 50 pg/mL (1 pM) of asialofetuin, providing the bead-based lectin microarray with the highest sensitivity among the reported lectin microarrays. Furthermore, multiplexed assay was performed, which allowed the simultaneous detection of multiple carbohydrate epitopes in a single reaction vessel. The glycosylation patterns of hepatocellular carcinoma associated immunoglobulin G were analyzed, and increased (α-1,6) core fucosylation and (α-2,6) sialylation patterns were observed, which may provide significant clinical evidence for disease diagnosis.

Structural characterization of N-linked oligosaccharides of laminin from rat kidney: changes during diabetes and modulation by dietary fiber and butyric acid

Carbohydrates of laminin, a family of large multidomain glycoproteins, have been implicated in various cellular activities including maintaining the protein structure, its function and also basement membrane integrity. During the course of our investigation, we observed that purified laminin from kidneys of control, diabetic, and dietary fiber- and butyric acid-treated diabetic rats showed differences in binding to extracellular matrix components. This prompted us to determine whether there are structural changes in laminin oligosaccharides. In this study, we have characterized a few major N-linked oligosaccharides isolated from purified laminin in various experimental groups, viz. normal, diabetic and diabetic rats fed with dietary fiber and butyric acid. Sugar composition, as identified by GLC, revealed the presence of mannose, galactose and N-acetylglucosamine. In order to study fine structures of the oligosaccharides, N-linked oligosaccharides of laminin were released by Peptide-N-glycosidase F digestion, end-labeled with 2-anthranilic acid and fractionated by lectin affinity chromatography. Furthermore, structural elucidation carried out by MALDI-TOF MS/MS analysis showed variations in the oligosaccharide sequence of laminin during diabetes which were altered by the feeding of dietary fiber and butyric acid.

Chemo-enzymatic synthesis of poly-N-acetyllactosamine (poly-LacNAc) structures and their characterization for CGL2-galectin-mediated binding of ECM glycoproteins to biomaterial surfaces

Poly-N-acetyllactosamine (poly-LacNAc) structures have been identified as important ligands for galectin-mediated cell adhesion to extra-cellular matrix (ECM) proteins. We here present the biofunctionalization of surfaces with poly-LacNAc structures and subsequent binding of ECM glycoproteins. First, we synthesized beta-GlcNAc glycosides carrying a linker for controlled coupling onto chemically functionalized surfaces. Then we produced poly-LacNAc structures with defined lengths using human beta1,4-galactosyltransferase-1 and beta1,3-N-acetylglucosaminyltransferase from Helicobacter pylori. These compounds were also used for kinetic characterization of glycosyltransferases and lectin binding assays. A mixture of poly-LacNAc-structures covalently coupled to functionalized microtiter plates were identified for best binding to our model galectin His(6)CGL2. We further demonstrate for the first time that these poly-LacNAc surfaces are suitable for further galectin-mediated binding of the ECM glycoproteins laminin and fibronectin. This new technology should facilitate cell adhesion to biofunctionalized surfaces by imitating the natural ECM microenvironment.

Paracoccin, a GlcNAc-binding lectin from Paracoccidioides brasiliensis, binds to laminin and induces TNF-α production by macrophages

Paracoccidioides brasiliensis components interact with host cells and can influence the pathogenesis of paracoccidioidomycosis (PCM). Among the components released by P. brasiliensis, gp 43 and a heavily glycosylated antigen with MM>160 kDa are the most recognized by serum antibodies from patients with PCM. In order to isolate the high MM glycoconjugate, we carried out affinity chromatography of a crude exoantigen preparation on immobilized jacalin. The bound fraction (JBE, jacalin binding exoantigen) consisted of a major antigen of high MM and frequently of an additional 70-kDa minor protein. This protein, designated paracoccin, exhibited selective binding to immobilized GlcNAc, a property that was used for its purification. The structural data of paracoccin obtained by mass spectrometry of tryptic peptides did not match any known protein. Anti-paracoccin serum localized the lectin on the surface of P. brasiliensis yeasts, especially in the budding regions. Paracoccin was able to interact with laminin in a dose-dependent manner. This interaction was inhibited by GlcNAc, followed by D-glucose and D-mannose, but not by D-galactose, N-acetyl-galactosamine or L-fucose. Interestingly, paracoccin induced both resident and elicited mouse peritoneal cavity macrophages to release high and persistent levels of TNF-alpha in vitro, a fact that was associated with high nitric oxide production in elicited cells. Because binding to laminin can favor yeast adhesion and invasion of host tissues, and overproduction of NO has been associated with suppression of cell immunity, paracoccin is suggested to play an important role in PCM pathogenesis.

Evanescent-field fluorescence-assisted lectin microarray: a new strategy for glycan profiling

Glycans have important roles in living organisms with their structural diversity. Thus, glycomics, especially aspects involving the assignment of functional glycans in a high-throughput manner, has been an emerging field in the postproteomics era. To date, however, there has been no versatile method for glycan profiling. Here we describe a new microarray procedure based on an evanescent-field fluorescence-detection principle, which allows sensitive, real-time observation of multiple lectin-carbohydrate interactions under equilibrium conditions. The method allows quantitative detection of even weak lectin-carbohydrate interactions (dissociation constant, K(d) > 10(-6) M) as fluorescent signals for 39 immobilized lectins. We derived fully specific signal patterns for various Cy3-labeled glycoproteins, glycopeptides and tetramethylrhodamine (TMR)-labeled oligosaccharides. The obtained results were consistent with the previous reports of glycoprotein and lectin specificities. We investigated the latter aspects in detail by frontal affinity chromatography, another profiling method. Thus, the developed lectin microarray should contribute to creation of a new paradigm for glycomics.

A heterogeneous immunofluorescence staining for laminin-1 and related basal lamina molecules in the dorsal root ganglia following constriction nerve injury

The bodies of primary sensory neurons and their satellite glial cells (SGCs) are limited by the basal laminae from extracellular matrix of the dorsal root ganglia (DRG). The basal laminae displayed uniform immunofluorescence staining for laminin-1 in the sections of rat intact (naive) DRG. A proximal or distal ligature of the spinal nerves resulted in a heterogeneous immunostaining for laminin-1 around neuron-SGC units in the sections of the corresponding DRG. The pattern of irregular laminin-1 immunofluorescence was more extensive in the ipsilateral than the contralateral DRG of the operated rats. The immunofluorescence for laminin-1 exactly coincided with binding of Concanavalin-A as well as immunostaining for type IV collagen in both naive DRG and DRG affected by nerve ligature. Nidogen immunostaining decreased or fully disappeared at the surface of the SGCs consistently with immunofluorescence staining for laminin-1, but retained or increased in the endothelial cells and ED-1 positive cells invaded the DRG affected by nerve ligature. The results indicate an alteration of the content of basal laminae surrounding the bodies of primary sensory neurons and their SGSs following nerve constriction injury. A modulation of the basal laminae may be related with other cellular and molecular alterations related with peripheral neuropathic pain, for example, expansion of sympathetic sprouts.

Identification and characterization of binding properties of Helicobacter pylori by glycoconjugate arrays

The microaerophilic bacterium Helicobacter pylori is well established for its role in development of different gastric diseases. Bacterial adhesins and corresponding binding sites on the epithelial surface allow H. pylori to colonize the gastric tissue. In this investigation, the adhesion of H. pylori to dot blot arrays of natural glycoproteins and neoglycoproteins was studied. Adhesion was detected by overlay with fluorescence-labeled bacteria on immobilized (neo)glycoproteins. The results confirmed the interaction between the adhesin BabA and the H-1-, Lewis b-, and related fucose-containing antigens. In addition, H. pylori bound to terminal alpha2-3-linked sialic acids as previously described. The use of a sabA mutant and sialidase treatment of glycoconjugate arrays showed that the adherence of H. pylori to laminin is mediated by the sialic acid-binding adhesin, SabA. The adhesion to salivary mucin MUC5B is mainly associated with the BabA adhesin and to a lesser extent with the SabA adhesin. This agrees with reports, that MUC5B carries both fucosylated blood group antigens and alpha2-3-linked sialic acids. The adhesion of H. pylori to fibronectin and lactoferrin persisted in the babA/sabA double mutant. Because binding to these molecules was abolished by denaturation rather than by deglycosylation, it was suggested to depend on the recognition of unknown receptor moieties by an additional unknown bacterial surface component. The results demonstrate that the bacterial overlay method on glycoconjugate arrays is a useful tool for exploration and the characterization of unknown adhesin specificities of H. pylori and other bacteria.

Lectin KM+-induced neutrophil haptotaxis involves binding to laminin

The lectin KM+ from Artocarpus integrifolia, also known as artocarpin, induces neutrophil migration by haptotaxis. The interactions of KM+ with both the extracellular matrix (ECM) and neutrophils depend on the lectin ability to recognize mannose-containing glycans. Here, we report the binding of KM+ to laminin and demonstrate that this interaction potentiates the KM+-induced neutrophil migration. Labeling of lung tissue by KM+ located its ligands on the endothelial cells, in the basement membrane, in the alveolus, and in the interstitial connective tissue. Such labeling was inhibited by 400 mM D-mannose, 10 mM Manalpha1-3[Manalpha1-6]Man or 10 microM peroxidase (a glycoprotein-containing mannosyl heptasaccharide). Laminin is a tissue ligand for KM+, since both KM+ and anti-laminin antibodies not only reacted with the same high molecular mass components of a lung extract, but also determined colocalized labeling in basement membranes of the lung tissue. The relevance of the KM+-laminin interaction to the KM+ property of inducing neutrophil migration was evaluated. The inability of low concentrations of soluble KM+ to induce human neutrophil migration was reversed by coating the microchamber filter with laminin. So, the interaction of KM+ with laminin promotes the formation of a substrate-bound KM+ gradient that is able to induce neutrophil haptotaxis.

Facile preparation of the alpha-Gal-recognizing Griffonia simplicifolia I-B4 isolectin

The B4 isolectin from Griffonia simplicifolia is of great utility as a reagent for the identification of alpha-D-galactopyranosyl end groups. Its separation from isolectins containing A subunits has been greatly improved by a simple, rapid procedure using a column of N-acetylgalactosamine coupled to vinyl sulfone-activated Sepharose 4B to selectively retain the A subunit-containing isolectins. The procedure has the advantages over previous affinity procedures of speed (the isolation of B4 isolectin can be achieved in one day), simplicity, and high degree of resolution of the B4 isolectin.

The Autoantigen of Anti-p200 Pemphigoid Is an Acidic Noncollagenous N-Linked Glycoprotein of the Cutaneous Basement Membrane

Anti-p200 pemphigoid is an autoimmune subepidermal blistering disease characterized by autoantibodies to a 200-kDa protein (p200) of the dermal-epidermal junction (DEJ). p200 has been demonstrated to be distinct from all major DEJ autoantigens and is thought to be important for cell-matrix adhesion. This study provides the first biochemical characterization of p200. Differential extraction experiments demonstrated that efficient recovery of p200 from the dermis was strongly dependent on the presence of reducing agents, suggesting that it forms highly insoluble oligomers and/or is extensively cross-linked to other extracellular matrix components by disulfide bonding. p200 was resistant to digestion with bacterial collagenase, whereas this treatment did degrade major collagenous proteins of the dermis, including type I, VI, and VII collagen. This finding firmly established the noncollagenous nature of p200. N-Glycosidase F reduced the molecular size of the p200 autoantigen from 200 to 190 kDa without decreasing its immunoreactivity. In contrast, digestion of p200 with neuraminidase, O-glycosidase, chondroitinase ABC, and heparitinase I had no effect on its electrophoretic mobility. These data suggest that the p200 molecule contains N-glycans but lacks O-linked oligosaccharides and chondroitin/heparan sulfate side chains. Two-dimensional gel electrophoresis demonstrated that p200 is an acidic protein with an isoelectric point of 5.4 to 5.6. Six different p200-specific sera recognized an identical protein spot of two-dimensionally separated dermal extracts, confirming that patients with this novel autoimmune disease indeed form a single pathobiochemical entity.

Identification of a Treponema pallidum laminin-binding protein

Host extracellular matrix (ECM) components represent ideal microbial adhesion targets that many pathogens use for colonization of tissues and initiation of infection. This study investigated the interaction of the spirochete Treponema pallidum with the ECM component laminin. To identify candidate laminin-binding adhesins, the T. pallidum genome was analyzed to predict open reading frames that encode putative outer membrane proteins, as these proteins interact directly with host ECM components. Subsequent recombinant expression of these proteins and analysis of their laminin-binding potential identified one protein, Tp0751, that demonstrated specific attachment to laminin. Tp0751 attached to laminin in a dose-dependent, saturable manner but did not attach to the ECM component collagen type I or IV or to the negative control proteins fetuin or bovine serum albumin. Sodium metaperiodate treatment of laminin reduced the Tp0751-laminin interaction in a concentration-dependent manner, suggesting that oligosaccharides play a role in this interaction. In addition, Tp0751-specific antibodies were detected in serum samples collected from both experimental and natural syphilis infections, indicating that Tp0751 is expressed in vivo during the course of infection. Collectively, these experiments identified Tp0751 as a laminin-binding protein that is expressed during infection and may be involved in attachment of T. pallidum to host tissues.

Purification and partial characterization of a 32-kilodalton sialic acid-specific lectin from Aspergillus fumigatus

Adherence of the opportunistic fungus Aspergillus fumigatus to the extracellular matrix components is considered a crucial step in the establishment of the infection. Given the high carbohydrate content of these glycoproteins and the role of carbohydrate-protein interactions in numerous adherence processes, the presence of a lectin in A. fumigatus was investigated. Different fungal extracts obtained by sonication or grinding in liquid nitrogen from resting or swollen conidia, as well as from germ tubes and mycelium, were tested by hemagglutination assays using rabbit erythrocytes. A lectin activity was recovered in all the extracts tested. However, sonication of resting conidia resulted in the highest specific activity. Purification of the lectin was achieved by gel filtration followed by ion-exchange and hydrophobic-interaction chromatographies. Analysis of the purified lectin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed an apparent molecular mass of 32 kDa, which is similar to that of the alkaline protease already identified from different strains of A. fumigatus. However, as evidenced by the use of an alkaline protease-deficient mutant, the two activities were supported by distinct proteins. In addition, hemagglutination inhibition experiments using different saccharides and glycoproteins demonstrated the specificity of the lectin for sialic acid residues. Together these results suggest that this lectin may contribute to the attachment of conidia to the extracellular matrix components through the recognition of the numerous terminal sialic acid residues of their carbohydrate chains.

Novel carbohydrate specificity of the 16-kDa galectin from Caenorhabditis elegans: binding to blood group precursor oligosaccharides (type 1, type 2, Talpha, and Tbeta) and gangliosides

Galectins, a family of soluble beta-galactosyl-binding lectins, are believed to mediate cell-cell and cell-extracellular matrix interactions during development, inflammation, apoptosis, and tumor metastasis. However, neither the detailed mechanisms of their function(s) nor the identities of their natural ligands have been unequivocally elucidated. Of the several galectins present in the nematode Caenorhabditis elegans, the 16-kDa "proto" type and the 32-kDa "tandem-repeat" type are the best characterized so far, but their carbohydrate specificities have not been examined in detail. Here, we report the carbohydrate-binding specificity of the recombinant C. elegans 16-kDa galectin and the structural analysis of its binding site by homology modeling. Our results indicate that unlike the galectins characterized so far, the C. elegans 16-kDa galectin interacts with most blood group precursor oligosaccharides (type 1, Galbeta1,3GlcNAc, and type 2, Galbeta1,4GlcNAc; Talpha, Galbeta1,3GalNAcalpha; Tbeta, Galbeta1,3GalNAcbeta) and gangliosides containing the Tbeta structure. Homology modeling of the C. elegans 16-kDa galectin CRD revealed that a shorter loop containing residues 66-69, which enables interactions of Glu(67) with both axial and equatorial -OH at C-3 of GlcNAc (in Galbeta1,4GlcNAc) or at C-4 of GalNAc (in Galbeta1,3GalNAc), provides the structural basis for this novel carbohydrate specificity.

The mushroom Marasmius oreades lectin is a blood group type B agglutinin that recognizes the Galalpha 1,3Gal and Galalpha 1,3Galbeta 1,4GlcNAc porcine xenotransplantation epitopes with high affinity

A blood group B-specific lectin from the mushroom Marasmius oreades (MOA) was investigated with respect to its molecular structure and carbohydrate binding properties. SDS-PAGE mass spectrometric analysis showed it to consist of an intact (H; 33 kDa) and truncated (L; 23 kDa) subunit in addition to a small polypeptide (P; 10 kDa). Isolation in the presence of EDTA produced only the H subunits, indicating that the latter two are formed by metalloprotease cleavage of the intact H subunit. Tryptic digestion of the H, L, and P polypeptide chains followed by mass spectral analysis supports this view. The lectin strongly precipitated blood group type B substance, was nonreactive with type A substance, and reacted weakly with type H substance. Carbohydrate binding studies reveal a high affinity for Galalpha1,3Gal (but not for the isomeric alpha1,2-, alpha1,4-, and alpha1,6-disaccharides); Galalpha1,3Galbeta1,4GlcNAc; and the type B branched trisaccharide. MOA also reacts strongly with murine laminin from the Engelbreth-Holm-Swarm sarcoma and bovine thyroglobulin, both of which contain multiple Galalpha1,3Galbeta1,4GlcNAc end groups. This linear B trisaccharide is a component of porcine tissues and organs, preventing their transplantation into humans. MOA also shares carbohydrate recognition of this trisaccharide with toxin A elaborated by Clostridium difficile.

Differential expression of an alpha-galactosyl-containing trisaccharide on high- and low-malignant murine sarcoma cells: identification and regulation

Past studies have shown that carbohydrate residues reactive with the Griffonia simplicifolia isolectin B4 (GS I-B4) are present on the surface of highly-malignant murine sarcoma cells but are lacking or expressed in much lower amounts on the surface of low-malignant cells isolated from the same parent tumors (Am J Pathol 111: 27; J Nat Cancer Inst 71: 1281). In the present study it is shown that an antibody which recognizes the trisaccharide Galalpha1-3Galbeta1-4GlcNAc- is reactive with the highly-malignant cells but is non-reactive with the low-malignant cells. Further studies show that the high-malignant cells not only bind GS 1-B4 but also bind Evonymus europaea lectin (which like GS I-B4 recognizes terminal galactose in alpha1-3 linkage) and Erythina crystagalli lectin (which recognizes sub-terminal galactose in the beta1-4 linkage--e.g., Galbeta1-4GlcNAc). In contrast, the low malignant cells bind Erythina crystagalli lectin as efficiently as the high malignant cells but do not bind (or bind much smaller amounts of) either GS I-B4 or Evonymus europaea lectin. The present studies also show that there is no significant difference between high- and low-malignant cells in expression of alpha-galactosidase activity. In contrast, the high-malignant cells express high levels of alpha-galactosyl transferase activity while this enzyme is virtually undetectable in low-malignant cells. Taken together, these studies indicate that differential expression of a single monosaccharide residue distinguishes high- and low-malignant murine sarcoma cells. These studies also identify a mechanism to account for surface carbohydrate differences between the high- and low-malignant cells.

Molecular modeling and mutagenesis studies of the N-terminal domains of galectin-3: evidence for participation with the C-terminal carbohydrate recognition domain in oligosaccharide binding

A model structure (Henrick,K., Bawumia,S., Barboni,E.A.M., Mehul,B. and Hughes, R.C. (1998) Glycobiology:, 8, 45-57) of the carbohydrate recognition domain (CRD, amino acid residues 114-245) of hamster galectin-3 has been extended to include N-terminal domain amino acid residues 91-113 containing one of the nine proline-rich motifs present in full-length hamster galectin-3. The modeling predicts two configurations of the N-terminal tail: in one the tail turns toward the first (SI) and last (S12) beta-strands of the CRD and lies at the apolar dimer interface observed for galectins -1 and -2. In the second folding arrangement the N-terminal tail lies across the carbohydrate-binding pocket of the CRD where it could participate in sugar-binding: in particular tyrosine 102 and adjacent residues may interact with the partly solvent exposed nonreducing N-acetylgalactosamine and fucose substituents of the A-blood group structure GalNAcalpha1,3 [Fucalpha1,2]Galbeta1,4GlcNAc-R. Binding studies using surface plasmon resonance of a recombinant fragment Delta1-93 protein containing residues 94-245 of hamster galectin-3 and a collagenase-derived fragment Delta1-103 containing residues 104-245, as well as alanine mutagenesis of residues 101-105 in Delta1-93 protein, support the prediction that Tyr102 and adjacent residues make significant contributions to oligosaccharide binding.

Recognition of fibronectin by Penicillium marneffei conidia via a sialic acid-dependent process and its relationship to the interaction between conidia and laminin

Adhesion of Penicillium marneffei conidia to the extracellular matrix protein laminin via a sialic acid-dependent process has previously been demonstrated. This study describes the interaction of P. marneffei conidia with fibronectin and examines the relationship of this process to the recognition of laminin via conidia. Immunofluorescence microscopy demonstrated that fibronectin bound to the surface of conidia and to phialides, but not to hyphae, in a pattern similar to that reported for laminin. Conidia were able to bind to fibronectin immobilized on microtiter plates in a concentration-dependent manner. However, binding to fibronectin (at any given concentration of protein and conidia) was less than that to laminin under equivalent conditions. Soluble fibronectin and antifibronectin antibody inhibited adherence of conidia to fibronectin in the plate adherence assay; soluble laminin also caused pronounced inhibition. Various monosaccharides and several peptides had no effect on adherence to fibronectin. However, N-acetylneuraminic acid abolished adherence to fibronectin, indicating that the interaction was mediated through a sialic acid-dependent process; the latter parallels observations of laminin binding by conidia. Fibronectin binding (and binding of laminin) was considerably reduced by prolonged preincubation of conidia with chymotrypsin, suggesting the protein nature of the binding site. Conidia from older cultures were more adherent to both immobilized fibronectin and laminin than conidia from younger cultures. Ligand affinity binding demonstrated the presence of a 20-kDa protein with the ability to bind both fibronectin and laminin. There would therefore appear to be a common receptor for the binding of fibronectin and laminin on the surface of P. marneffei, and the interaction described here maybe important in mediating attachment of the fungus to host tissue.

Kinetic measurements of binding of galectin 3 to a laminin substratum

Galectin 3, a beta-galactoside binding protein, contains a C-terminal carbohydrate recognition domain (CRD) and an N-terminal segment including multiple repeats of a proline/tyrosine/glycine-rich motif. Previous work has shown that galectin 3 but not the isolated CRD binds to laminin, a multivalent ligand, with positive cooperativety indicating the formation of multiple interactions although the lectin in solution is monomeric. Using surface plasmon resonance, we find that hamster galectin 3 at sub-micromolar concentrations or its isolated CRD at all concentrations binds to a laminin substratum with similar association (k(ass); 10-30,000 M(-1) S(-1)) and dissociation (k(diss); 0.2-0.3 S1(-1)) rates and weak affinity (Ka; 1-3 x 10(5) M(-1)). At higher concentrations of galectin 3 the off rate decreases ten fold leading to increased affinity. Ligation of an N-terminal epitope of galectin 3 with a monoclonal Fab fragment increases association and dissociation rates ten fold. A recombinant protein obtained by deletion of the first 93 N-terminal residues binds to laminin with positive cooperativity and a slowly dissociating fraction (K(diss); 0.002 S(-1)) accumulates on the substratum. The data suggest that homophilic interactions between CRD as well as N terminal domains are implicated in galectin 3 aggregation on the substratum leading to positive binding cooperativity.

Natural autoantibody to galectin-9 in normal human sera

Antibodies to certain self-antigens are detected in normal individuals as well as in patients with autoimmune diseases. Natural autoantibodies found in normal human sera are thought to act as an immune regulator, a functional controller of specific proteins, or the first-line defense against pathogenic microorganisms. In the course of screening human pancreatic islet cDNA library with human sera, we found that autoantibodies to galectin-9 and its unique isoform are present in normal healthy individuals. Galectin-9 antibody was detected in all 44 human sera tested by the immunoprecipitation assays, suggesting a widespread presence of galectin-9 autoantibodies in humans. The reactivity of the sera to galectin-9 was not inhibited by lactose or endoglycosidase treatment, indicating that the reactivity was not due to a nonspecific lectin-carbohydrate interaction. We also demonstrated by RT-PCR that galectin-9 and its isoform are expressed in a variety of human tissues such as pancreatic islets, liver, lung, and tonsils as well as HeLa and Jurkat cell lines. Thus, although it has been reported previously that human galectin-9 is expressed mainly in immune cells and tissues, the current work suggests that the expression of galectin-9 and its isoform is not tissue-restricted and natural autoantibodies against them are present in normal human sera. The significance of these autoantibodies needs to be studied further.

Definition and characterization of chicken Gal alpha(1,3)Gal antibodies

BACKGROUND

The Gal alpha(1,3)Gal epitope is of interest as, in pig-to-primate xenotransplantation, it is the major target of naturally occurring human IgM and IgG antibodies, leading to hyperacute rejection. Human and Old World monkeys make anti-Gal alpha(1,3)Gal antibodies as they lack a functional gene and do not express Gal alpha(1,3)Gal. Interestingly, the cultured fibroblasts of some other species, such as chickens, have been reported also not to express Gal alpha(1,3)Gal--if this is true for other tissues, and chickens do not express Gal alpha(1,3)Gal antigen, then they would have anti-Gal antibodies--which could have diagnostic and therapeutic value, particularly as chicken antibodies do not fix mammalian complement.

METHODS

Standard serological methods were used to characterize the antibodies. Several baboons received pig kidney xenografts that had been perfused with hyperimmune chicken anti-Gal antibodies.

RESULTS AND CONCLUSIONS

We now demonstrate that chickens do not express Gal alpha(1,3)Gal on their red cells, leukocytes, or tissues, and that their serum contains large amounts of anti-Gal alpha(1,3)Gal antibodies. In addition, chickens could be immunized to produce high-titer, high-avidity antibodies (9.5x10(9) M(-1))--an avidity considerably greater than that of the Gal alpha(1,3)Gal binding lectin IB4 (2.9x10(8) M(-1)) or Gal antibodies in human serum (2.2x10(5) M(-1)). Chicken antibodies, obtained from both normal and immunized chickens, could block the in vitro cytolysis of pig endothelial cells or lymphocytes by human or baboon antibodies. However, such antibodies tested in vivo in pig-to-baboon xenotransplantation failed to block hyperacute rejection and, indeed, may have accelerated this.

alpha-Gal epitopes in animal tissue glycoproteins and glycolipids

alpha-Gal terminated saccharides are present on the cell surface both as glycolipids and glycoproteins in all mammals except Old World monkeys and humans. The structural diversity among identified saccharides terminated by this epitope in animal tissues is steadily increasing. The majority of these saccharides have the alpha-Gal linked to lactosamine but other core saccharides exist. The alpha-Gal terminated saccharides are recognized by the immune system as a specific antigen and antibodies directed to the alpha-Gal, which do not cross-react with the classic blood group B trisaccharide, are found in man and Old World monkeys. Similar to other complex carbohydrate cell surface antigens, the alpha-Gal epitope is heterogeneously distributed in different organs and in different cells within an organ. It is present on the vascular endothelium and it is the primary target for human naturally occurring antibodies following pig to primate/man xenotransplantation leading to hyperacute rejection of the graft. Important for the future will be to further structurally characterize this antigen system, its cellular/subcellular distribution, and to identify possible of additional glycosyltransferases, related to the already described alpha 1,3galactosyltransferase that may explain the structural diversity. Such information will be of importance in the studies of, for example, the pathogenesis of autoimmune diseases and for the production of genetically modified pigs to prevent xenograft rejection.

Lectins inhibit periodontal ligament fibroblast attachment, spreading and migration on laminin substrates

The ways in which carbohydrate signals from the extracellular matrix influence the responses of periodontal ligament (PDL) fibroblasts are essentially unknown. The purpose of this study, using video digital image analysis, was to examine the effects of lectins on the attachment, spreading and migrational responses of rat periodontal ligament fibroblasts on the highly glycosylated glycoprotein laminin (LN) in vitro. PDL fibroblasts were isolated from rat molar teeth and grown in culture. Bound LN and control substrates (bovine serum albumin and untreated plastic) were incubated with solutions of either wheatgerm agglutinin (WGA), specific for N-acetylglucosamine, or concanavalin A (ConA), specific for mannose, in 96-well plates. Unbound lectin was rinsed away and 10.0 x 10(3) cells were seeded per well and allowed to attach for 1.5 h. Incubation of LN substrates with WGA, prior to the addition of any cells, inhibited PDL fibroblast binding more than 5-fold. ConA, however, had no effect on cell binding but inhibited mean individual cell spreading nearly 3-fold under similar assay conditions. The effects could be prevented by adding each lectin's respective specific sugar. The lectins had no effects on the control substrates. In a 24-h cell migration assay WGA and ConA both significantly inhibited migration of PDL fibroblasts. It is likely that WGA inhibited cell attachment and cell migration, by binding to oligosaccharides and blocking access to adjacent polypeptide cell recognition sequences on LN. The results from the ConA experiments, where binding was allowed but spreading was severely inhibited, suggest a possible informational role for the carbohydrates present on LN.

Sialic acid-dependent recognition of laminin by Penicillium marneffei conidia

Immunofluorescence microscopy demonstrated that laminin bound to the surface of Penicillium marneffei conidia. Attachment of P. marneffei conidia in an adherence assay was inhibited by soluble laminin and anti-laminin antibody. N-Acetylneuraminic acid abolished adherence, indicating an interaction mediated by a sialic acid-specific lectin.

Sialic acid-dependent recognition of laminin and fibrinogen by Aspergillus fumigatus conidia

In an attempt to define the molecular basis of the adherence of Aspergillus fumigatus conidia to the host tissues, a step which might be mediated by the recognition of basement membrane laminin or fibrinogen, we analyzed the binding of these glycoproteins by flow cytometry and a microtiter plate adherence assay. Flow cytometry revealed that the binding of fluorescein isothiocyanate-labeled laminin to conidia was saturable and specific. Moreover, the ability of conidia to bind laminin increased with their maturation. Competition experiments showed a cross-reactivity between laminin and fibrinogen binding and a lack of interactions with glycosaminoglycans. In addition, the binding of laminin was not inhibited by the different adhesive synthetic peptides tested. Furthermore, the microtiter plate assay of adherence to chymotrypsin degradation products of laminin or fibrinogen purified by gel filtration suggested a unique binding site common to sequential degradation fragments or the presence of multiple binding sites on the two ligands. Therefore, the role of carbohydrates in the recognition process was investigated. Among the carbohydrates tested, constitutive of the conidial wall or of the oligosaccharide side chains of laminin and fibrinogen, only N-acetylneuraminic acid and sialyllactose inhibited the binding of these glycoproteins to conidia. In conclusion, these results strengthen the idea that the laminin and fibrinogen receptors in A. fumigatus are identical and suggest an interaction mediated by a sialic acid-specific lectin of the conidial wall.

A soluble form of alpha1,3-galactosyltransferase functions within cells to galactosylate glycoproteins

It has been assumed that membrane-bound glycosyltransferases function within the Golgi apparatus to glycosylate glycoproteins. We now report, however, that a truncated, soluble recombinant form of the murine alpha1,3-galactosyltransferase expressed in human 293 cells is highly efficient and comparable to the full-length enzyme in alpha-galactosylating both newly synthesized membrane-associated and secreted glycoproteins. Although the soluble enzyme was secreted by cells as expected, we also found that the full-length, membrane-associated form was secreted. Unexpectedly, both secreted forms are cleaved identically at two primary sites within the stem region by endogenous protease(s) at the indicated positions in the sequence 73KDWW (downward arrow) FPS (downward arrow) WFKNG. These results demonstrate that the soluble alpha1,3-galactosyltransferase is functional within the cell and that specific proteolysis occurs in the stem region. The widespread occurrence of different soluble glycosyltransferases secreted by cells suggests that normal glycoconjugate biosynthesis may involve cooperation between membrane-bound and soluble enzymes.

Identification of the N-acetylneuraminyllactose-specific laminin-binding protein of Helicobacter pylori

The interaction of the gastroduodenal pathogen Helicobacter pylori with the glycoprotein laminin was investigated. Binding of 125I-radiolabelled laminin in a liquid-phase assay by both hemagglutinating and poorly hemagglutinating strains was rapid, saturable, specific, partially reversible, of high affinity, and insensitive to pH. Inhibition of laminin binding by fetuin, but not asialofetuin, and reduced bacterial binding to periodate- or sialidase-treated laminin indicated that glycosylation, particularly sialylation, was important for laminin binding by H. pylori. Inhibition experiments with monosaccharides, disaccharides, and trisaccharides showed that the strains bound to a region spanning a trisaccharide. In particular, inhibition and displacement studies showed that binding to the trisaccharide N-acetylneuraminyl-alpha(2-3)-lactose [NeuAc(2-3)Lac] was preferential to that to the NeuAc(2-6)Lac isomer. Complete inhibition of laminin binding by both hemagglutinating and poorly hemagglutinating strains was achieved only when isolated lipopolysaccharide (LPS) was used as an inhibitor in combination with heat or protease treatment of H. pylori cells, thereby confirming the involvement of both LPS and a protein adhesin in laminin binding. Further inhibition experiments indicated that the protein receptor, rather than LPS, on H. pylori bound NeuAc(2-3)Lac. By using a Western blotting procedure, a 25-kDa outer membrane protein was identified as mediating laminin binding by both hemagglutinating and poorly hemagglutinating H. pylori strains. The specificity of binding was confirmed by complete inhibition of laminin binding by the 25-kDa protein with NeuAc(2-3)Lac. The data collectively suggest that a 25-kDa outer membrane protein acts in a lectin-like manner with LPS to mediate attachment of H. pylori to laminin.

Purification and carbohydrate-binding specificity of Agrocybe cylindracea lectin

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

Detection of sugar residues in rabbit embryo teeth with lectin-horseradish peroxidase conjugate: II. A light microscopal study

The cellular distribution and changes of sugar residues during tooth development in embryos of the rabbit Oryctolagus cuniculus were investigated by using horseradish peroxidase-conjugated lectins (lectin-HRP). The lectins SBA, ECA, and LTA show no binding to any region of the dental cap and bell stages, whereas BS-1 and UEA-1 bind to dental cells at both stages. Appropriate control studies confirmed the specificity of the binding of the lectins. At cap stage, the lectins BS-1 and UEA-1 show moderate binding to the (pre)-ameloblast and (pre)-odontoblast cells. These results suggest that the acetylgalactosamine and alpha-L-fucose residues present in (pre)-ameloblasts and (pre)-odontoblasts, respectively, are common to determined but relatively undifferentiated cells capable of forming matrices of hard tissues. Since the odontoblast and ameloblast express dentin and enamel, respectively, it can be speculated that the abundance of these residues in these cells might be associated with the maintenance of the capacity of the cells to produce such matrices. At the bell stage, the odontoblasts display considerable amounts of alpha-L-fucose, whereas alpha-L-fucose is poorly localized in ameloblasts. However, ameloblasts contain significant quantities of N-acetylgalactosamine, whereas only a diffuse positivity for this carbohydrate is apparent in odontoblasts. The marked changes of the glycosylation pattern of these glycoconjugates might indicate that they play a role during the cell-to-cell interaction and might also be involved in the odontoblastic and ameloblastic functional activity. Such a possibility is entirely speculative until specific in vitro experiments are conducted.

Calreticulin binding affinity for glycosylated laminin

Several lines of evidence indicate that calreticulin has lectin-like properties. As a molecular chaperone, calreticulin binds preferentially to nascent glycoproteins via their immature carbohydrates; this property closely resembles that seen for calnexin, a chaperone with extensive molecular identity to calreticulin. A cell surface form of calreticulin also exhibits lectin-like properties, binding specific oligomannosides including those covalently linked to laminin. In the present study we examined the interaction between calreticulin and laminin by means of surface plasmon resonance. The results show that calreticulin specifically binds to glycosylated laminin but fails to specifically bind tunicamycin-derived unglycosylated laminin or bovine serum albumin. Calreticulin binding to glycosylated laminin requires calcium and is abolished in the presence of EDTA. Scatchard analysis of binding yields an apparent association constant, Ka, of 2.1 +/- 0.9 x 10(6) m-1 while kinetic analysis yields an estimate of the association on rate, (Kassoc), as 2 x 10(5) m-1 s-1. The composite results support calreticulin's lectin-like properties as well as its proposed role in laminin recognition, both in the cell interior and on the cell surface.

Transcriptional regulation of alpha1,3-galactosyltransferase in embryonal carcinoma cells by retinoic acid. Masking of Lewis X antigens by alpha-galactosylation

Treatment of mouse teratocarcinoma F9 cells with all-trans-retinoic acid (RA) causes a 9-fold increase in steady-state levels of mRNA for UDP-Gal:beta-D-Gal alpha1,3-galactosyltransferase (alpha1,3GT) beginning at 36 h. Enzyme activity rises in a similar fashion, which also parallels the induction of laminin and type IV collagen. Nuclear run-on assays indicate that this increase in alpha1,3GT in RA-treated F9 cells, like that of type IV collagen, is transcriptionally regulated. Differentiation also results in increased secretion of soluble alpha1,3GT activity into the growth media. The major alpha-galactosylated glycoprotein present in the media of RA-treated F9 cells, but not of untreated cells, was identified as laminin. Differentiation of F9 cells is accompanied by an increase in alpha-galactosylation of membrane glycoproteins and a decrease in expression of the stage-specific embryonic antigen, SSEA-1 (also known as the Lewis X antigen or LeX), which has the structure Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-R. However, flow cytometric analyses with specific antibodies and lectins, following treatment of cells with alpha-galactosidase, demonstrate that differentiated cells contain LeX antigens that are masked by alpha-galactosylation. Thus, RA induces alpha1,3GT at the transcriptional level, resulting in major alterations in the surface phenotype of the cells and masking of LeX antigens.

Cell surface calreticulin is a putative mannoside lectin which triggers mouse melanoma cell spreading

B16 mouse melanoma cells adhere to and spread on laminin. We have previously shown that cell spreading is uncoupled from adhesion when unglycosylated laminin is used as a substratum; spreading was restored by a Pronase digest of laminin which became inactive when it was specifically depleted of its mannoside peptides; spreading was also specifically restored by mannosides such as mannan, Man9, and Man6, but not Man3. The effector mannosides bind to a cell surface receptor, previously shown by direct and indirect methods. We have now identified the receptor as cell surface calreticulin by isolating it via mannan affinity chromatography and showing its sequence identity with mouse calreticulin. Anti-calreticulin antibodies confirm this identity, decorate the B16 cell surface, and block cell spreading. Purified B16 cell calreticulin from whole cell lysates successfully competes with cell surface calreticulin and prevents cell spreading. The composite data implicate cell surface calreticulin as a putative lectin that must be occupied to initiate spreading of laminin-adherent B16 cells.

Isolation of a melibiose-binding protein from human spleen

A melibiose-binding protein was isolated from human spleen by serial affinity chromatography on lactose-, mannose-, and melibiose-Sepharose. The purified protein agglutinated rabbit erythrocytes and re-bound to melibiose, but did not bind to murine nor human laminin. The protein was composed of approximately 58 kDa and 26 kDa polypeptides. The polypeptides were detected in buffy coat cell extracts and they were synthesized in vitro by B lymphoblastoid cells. The polypeptides did not react with anti-galaptin, anti-C-reactive protein, anti-amyloid P, anti-keratin, and anti-rat lung lectin 29 sera. The 58 kDa polypeptide reacted very weakly with anti-core-specific lectin serum and reacted with anti-IgG serum. The data suggest that the major protein isolated is an anti-Ga1 alpha 1-->6 immunoglobulin.

Rodent myoblast interactions with laminin require cell surface glycoconjugates but not laminin glycosyl groups

Laminin glycosyl groups are necessary for the spreading of murine melanoma cells which become attached to this glycoprotein. Laminin has been implicated in myogenesis but the potential role of its glycosyl groups in this process has not been examined. In this study we report the effects of the carbohydrate moieties of laminin on myoblast adhesion, spreading, and differentiation. Unglycosylated laminin from tunicamycin-treated cultures of a mouse cell line, M1536 B3, was used in the experiments. Glycosylated laminin from a murine tumor and from cultures of M1563 B3 cells served as controls. Cell binding experiments with C2C12 mouse myoblasts showed that the cells preferred a laminin-coated surface, compared to the uncoated plastic surface (nontissue culture wells). Myoblasts did not distinguish between glycosylated and unglycosylated laminin substrates. Both glycosylated and unglycosylated forms of laminin promoted myoblast growth and differentiation. In contrast, cells on uncoated plastic surfaces grew very slowly and did not further differentiate. The L6 rat myoblast response to glycosylated and unglycosylated laminin was the same. These results indicate that although rodent myoblasts in culture require a laminin substratum for spreading, growth, and differentiation on a proprietary plastic surface, laminin carbohydrates are not implicated in those cellular responses. In contrast, parallel studies using the lectin, Con A, indicate that cell surface glycoconjugates of myoblasts are implicated in the response of these cells to a laminin substratum.

Glycolipid receptors for attachment of Mycoplasma hyopneumoniae to porcine respiratory ciliated cells

Glycolipid receptors for Mycoplasma hyopneumoniae attachment were analyzed by using a thin-layer chromatography (TLC) overlay assay. M. hyopneumoniae bound specifically to sulfatide, globoside, and monosialoganglioside GM3. No binding to sphingomyelin, cerebroside, lactosyl ceramide, ceramide trihexoside, monosialogangliosides GM1 and GM2, disialogangliosides (GD1a, GD1b, and GD3), trisialoganglioside (GT1b), cholesterol, cholesterol sulfate, palmitic acid, tripalmitin, or cholesteryl palmitate was detected. Total lipids extracted from cilia of the swine respiratory epithelium, the natural targets of M. hyopneumoniae infection, were also separated on TLC plates and overlaid with mycoplasmas. M. hyopneumoniae bound specifically to three ciliary glycolipids identified as La, Lb, and Lc. Binding to Lc was stronger than to La and Lb. All three lipids were believed to be sulfated glycolipids, as determined by laminin binding and staining with azure A. Lc was identified as a putative sulfatide because it has a mobility similar to that of authentic sulfatide and comigrated with sulfatide on TLC plates. Laminin bound to La, Lb, and Lc and produced dose-dependent inhibition of adherence of the mycoplasma to the three ciliary receptors. Binding of the mycoplasma to sulfatide, La, Lb, and Lc was partially inhibited by dextran sulfate, heparin, fucoidan, mucin, and chondroitin sulfate B. These substances blocked the adherence of M. hyopneumoniae to cilia and ciliated cells as shown in a previous study (Q. Zhang, T. F. Young, and R. F. Ross, Infect. Immun. 62:1616-1622, 1994). These results indicate that La, Lb, and Lc are the major native receptors for M. hyopneumoniae adherence to ciliated cells.

The HMW1 adhesin of nontypeable Haemophilus influenzae recognizes sialylated glycoprotein receptors on cultured human epithelial cells

Disease due to nontypeable Haemophilus influenzae begins with colonization of the upper respiratory tract mucosa. We recently reported that two surface-exposed high-molecular-weight proteins (HMW1 and HMW2) expressed by a prototypic strain of nontypeable H. influenzae mediate attachment to cultured epithelial cells. In the present study, we examined the nature of the epithelial cell receptor with which HMW1 interacts. Both proteinase K pretreatment and periodate oxidation of epithelial monolayers resulted in a marked decrease in HMW1-mediated binding, suggesting interaction with a glycoprotein structure. Treatment with peptide-N-glycosidase F produced a similar decrease in attachment and thereby provided further evidence for this conclusion. Desialylation of the epithelial cell surface also reduced binding, implying the presence of sialic acid in the receptor structure. Furthermore, lectins specific for terminal alpha 2-3-linked sialic acid were capable of inhibiting HMW1-mediated attachment. In summary, our results indicate that the HMW1 adhesin interacts with a glycoprotein receptor containing N-linked oligosaccharide chains with sialic acid in an alpha 2-3 configuration.

Localisation of alpha(2,3) and alpha(2,6) linked terminal sialic acid groups in human trabecular meshwork

Sialic acid specific lectins were used to localise isomers of sialyl glycosides in human trabecular meshwork (TM) at the ultrastructural level. A lectin immunogold method demonstrated that sialic groups were concentrated on the endothelial surface of Schlemm's canal (SC) and in the adjacent juxta-canalicular tissue (JCT). One sialyl glycoside, alpha(2,6) linked N-acetyl neuraminic acid, was present mainly on the luminal aspect of the SC endothelium and in the cytoplasm of the JCT cells. Another, alpha(2,3) linked N-acetyl neuraminic acid, was localised predominantly to the extracellular fibrillar material of the JCT. The existence of a topographical segregation of these two sialyl glycosides within the TM supports the view that highly charged anionic molecules may be of significance in regulating aqueous outflow.

Rat olfactory neurons can utilize the endogenous lectin, L-14, in a novel adhesion mechanism

L-14 is a divalent, lactosamine-binding lectin expressed in many vertebrate tissues. In the rat nervous system, L-14 expression has been observed previously in restricted neuronal subsets within the dorsal root ganglia and spinal cord. In this study we report that L-14 is expressed by nonneuronal cells in the rat olfactory nerve. We demonstrate that L-14 binds and co-localizes with two ligands in the rat olfactory system: a beta-lactosamine-containing glycolipid, and a putative member of the laminin family. The former is expressed on the surfaces of nascent olfactory axons originating from neuron cell bodies in the olfactory epithelium. The latter is present in the extracellular matrix of the axonal path leading to synaptic targets in the olfactory bulb. In vitro, we find that recombinant L-14 promotes primary olfactory neuron adhesion to two laminin family members, and promotes intercellular adhesion. Both activities are dose-dependent, and are independent of integrin-mediated mechanisms. We have thus found that L-14 can serve two distinct adhesive functions in vitro, and propose that L-14 in vivo can promote olfactory axon fasciculation by crosslinking adjacent axons and promote axonal adhesion to the extracellular matrix.

The adhesive specificity of the soluble human lectin, IgE-binding protein, toward lipid-linked oligosaccharides. Presence of the blood group A, B, B-like, and H monosaccharides confers a binding activity to tetrasaccharide (lacto-N-tetraose and lacto-N-neotetraose) backbones

The immunoglobulin E-binding protein, epsilon BP (also known as CBP35, Mac-2, L-34, and L-29), is a beta-galactoside-binding protein of approximately 30 kDa and a member of the animal lectin family termed S-type or S-Lac. Multiple biological activities have been attributed to this lectin such as mediation of IgE binding to the surface of Langerhans cells and activation of mast cells through binding to the high affinity IgE receptor. In order to better understand the cell-binding activity and the proposed role for epsilon BP as a biological response modifier, we have studied the specificity of binding of the radioiodinated epsilon BP to a series of lipid-linked, structurally defined oligosaccharide sequences of the lacto/neolacto family. The results show that the minimum lipid-linked oligosaccharides that can support epsilon BP binding are pentasaccharides of the lacto/neolacto series and that the lectin binds more strongly to oligosaccharides of this family that bear the blood group A, B, or B-like determinants than to those bearing blood group H. This preferential binding of epsilon BP is also manifest with whole cells, as erythrocytes of blood groups A and B are more strongly bound by epsilon BP than those of blood group O. Blood group Le(a) and Le(x) sequences are not bound by the lectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinoic acid enhances adhesiveness, laminin and integrin beta 1 synthesis, and retinoic acid receptor expression in F9 teratocarcinoma cells

The teratocarcinoma-derived F9 cells respond to retinoic acid (RA) and RA plus dibutyrylcyclic adenosine monophosphate (dcAMP) by differentiating into endoderm cells, which elaborate a laminin and type IV collagen-rich matrix. We found that the induction of differentiation is accompanied by a small but consistent increase in cell adhesiveness to a variety of substrates, including laminin. Therefore we investigated biochemical mechanisms involved in this phenomenon. Endoglycosidase treatment showed that laminin contains complex and hybrid oligosaccharide structures. RA enhanced general biosynthesis of laminin without a specific increase in galactose incorporation: this sugar was mainly in polylactosamine structures in the A chain of laminin and as terminal galactose alpha 1,3 galactose in the B chain. Laminin receptor analysis showed that RA decreased laminin binding protein-37 (LBP-37) but increased the amount of beta 1 integrin, suggesting the involvement of beta 1 integrin in the attachment process. Northern blot analysis showed increased expression of retinoid receptors within hours of RA exposure. These studies demonstrate that RA increases cell to substrate interactions by increasing the biosynthesis of laminin and beta 1 integrin. These effects are most likely subsequent to the RA-induced biosynthesis of the retinoid receptors.

Novel N-glycosylation in eukaryotes: laminin contains the linkage unit beta-glucosylasparagine

The linkage unit to protein of N-linked carbohydrate in eukaryotic glycoproteins consists of N-acetylglucosamine, coupled to the amido nitrogen of asparagine. Additional N-glycosyl linkage units have been unequivocally proven to exist only in the cell surface glycoproteins of various bacteria. Based on immunological analyses, isolation and chemical characterization, we report that one of these units, namely glucose linked to asparagine, exists in the mammalian protein laminin, an extracellular basement membrane component. This finding and the occurrence of identical disaccharide structures in archaebacterial cell surface glycoproteins and mammalian basement membrane protein complexes points towards a conserved and distinct function of these extracellular structural elements. In addition, a method is described to uncover a masked epitope in fixed tissues by chemical O-deglycosylation. This has allowed to morphologically localize the antigen beta-Glc-Asn by immunofluorescence to the basement membranes of kidney glomeruli.

Selective modulation of the interaction of alpha 7 beta 1 integrin with fibronectin and laminin by L-14 lectin during skeletal muscle differentiation

The alpha 7 beta 1 integrin was originally identified and isolated from differentiating skeletal muscle and shown to be a laminin-binding protein (Song et al. (1992) J. Cell Biol. 117, 643–657). Expression of the alpha 7 gene and protein are developmentally regulated during skeletal muscle differentiation and have been used to identify cells at distinct stages of the myogenic lineage (George-Weinstein et al. (1993) Dev. Biol. 156, 209–229). The lactoside-binding protein L-14 exists as a dimer and has been localized on a variety of cells, in association with extracellular matrix. During myogenesis in vitro, L-14 is synthesized within replicating myoblasts but it is not secreted until these cells commence terminal differentiation and fusion into multinucleate fibers (Cooper and Barondes, J. Cell Biol. (1990) 110, 1681–1691). Addition of purified L-14 to myogenic cells plated on laminin inhibits myoblast spreading and fusion, suggesting that the L-14 lectin regulates muscle cell interactions with the extracellular matrix that are germane to myogenic development (Cooper et al. (1991) J. Cell Biol. 115, 1437–1448). We demonstrate here, using affinity chromatography and immunoblots, that alpha 7 beta 1 also binds to fibronectin and to the L-14 lectin. L-14 binds to both laminin and to the alpha 7 beta 1 integrin, and it can effectively inhibit the association of laminin and this integrin. Modulation of alpha 7 beta 1 interaction with its ligands by L-14 is selective: L-14 does not bind to fibronectin, nor does it interfere with the binding of fibronectin to alpha 7 beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)