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PubMed1995

The surface glycoconjugates of parasitic protozoa: potential targets for new drugs.

Protozoan parasites are the cause of many disease in humans and their domestic livestock. Glycoconjugates (i.e. glycoproteins, glycolipids) on the cell surface of these extremely diverse and very primative eukaryotes play a crucial role in determining the specificity of the host-parasite interaction and in protecting the parasites within their respective hosts. These molecules frequently share a common structural feature in that they are attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) glycolipid. While GPI protein-membrane anchors are ubiquitous among the eukaryotes, they are used with exceptionally high frequency in the protozoa. Some kinetopastid parasites also synthesise very high levels of GPI-related glycolipids that are not linked to protein. Thus GPI-anchored molecules or free GPI glycolipids send to dominate the cell surface molecular architecture of these organisms. The highly elevated levels and specialised nature of GPI metabolism in the kinetoplastid and other parasites suggests that the GPI biosynthetic pathway might be a good target for the development of new chemotherapeutic agents. This article reviews the wide range of functions that GPI protein anchors and GPI-related glycolipids are thought to perform in these organisms and some aspects of their biosynthesis.

Animals↗

PubMed1994

Occurrence of antibodies against chlamydial lipopolysaccharide in human sera as measured by ELISA using an artificial glycoconjugate antigen.

An artificial glycoconjugate containing, as a ligand, the deacylated carbohydrate backbone of a recombinant Chlamydia-specific lipopolysaccharide was used as a solid-phase antigen in ELISA to measure antibodies against chlamydial LPS. The specificity and reproducibility of the assay was shown by using a panel of prototype monoclonal antibodies representing the spectrum of antibodies also occurring in patient sera. These mAbs recognized Chlamydia-specific epitopes [alpha 2-->8-linked disaccharide of 3-deoxy-D-manno-octulosonic acid (Kdo) or the trisaccharide alpha Kdo-(2-->8)-alpha Kdo-(2-->4)-alpha Kdo] or those shared between chlamydial and Re-type LPS (alpha Kdo, alpha 2-->4-linked Kdo disaccharide). The assay was used to measure IgG, IgA and IgM antibodies against chlamydial LPS in patients with genital or respiratory tract infections. In comparison to the results obtained with sera from blood donors, it became evident that both types of infection result in significant changes in the profile of LPS antibodies.

Antibodies, Bacterial↗

PubMed2006

Functional interaction of Escherichia coli heat-labile enterotoxin with blood group A-active glycoconjugates from differentiated HT29 cells.

Human colon adenocarcinoma cells (HT29-ATCC) and the clone HT29-5F7 were cultured under conditions that differentiate cells to a polarized intestinal phenotype. Differentiated cells showed the presence of junctional complexes and intercellular lumina bordered by microvilli. Intestinal brush border hydrolase activities (sucrase, aminopeptidase N, lactase and maltase) were detected mainly in differentiated HT29-ATCC cells compared with the differentiated clone, HT29-5F7. The presence of non-GM1 receptors of Escherichia coli heat-labile enterotoxin (LT-I) on both types of differentiated HT29 cells was indicated by the inability of cholera toxin B subunit to block LT-I binding to the cells. Binding of LT-I to cells, when GM1 was blocked by the cholera toxin B subunit, was characterized by an increased number of LT-I receptors with respect to undifferentiated control cells. Moreover, both types of differentiated cells accumulated higher amounts of cyclic AMP in response to LT-I than undifferentiated cells. Helix pomatia lectin inhibited the binding of LT-I to cells and the subsequent production of cyclic AMP. LT-I recognized blood group A-active glycosphingolipids as functional receptors in both HT29 cell lines and the active pro-sucrase form of the glycoprotein carrying A-blood group activity present in HT29-ATCC cells. These results strongly suggest that LT-I can elicit an enhanced functional response using blood group A-active glycoconjugates as additional receptors on polarized intestinal epithelial cells.

ABO Blood-Group System↗

PubMed1987

Detection of mucus glycoconjugates in human conjunctiva by using the lectin-colloidal gold technique in TEM. III. A quantitative study in asymptomatic contact lens wearers.

We characterized the mucus glycoconjugates produced by goblet and non-goblet epithelial cells in asymptomatic contact lens (CL) wearers. We employed four lectins (proteins of vegetal origin which specifically recognize glycosidic residues: WGA, PNA, SBA and ConA) conjugated with colloidal gold as ultrastructural marker, at Transmission Electron Microscopy. A computerized quantitative analysis was carried out in order to compare the results from the CL wearers to those from the control patients. Goblet cells produce different amount of glycosidic residues, in particular, a significant decrease in the distribution of sialic acid, N-acetylglucosamine, N-acetylgalactosamine, galactose-N-acetylgalactosamine and mannose was observed. The content of glycosidic residues in the mucus vesicles of the non-goblet epithelial cells appeared unchanged as to the normal situation. We speculate that the CL could possibly contribute to the failure of the tear film stability by altering the production of mucus.

Adult↗

PubMed1989

Glycoconjugates in exfoliation syndrome. A lectin histochemical study of the ciliary body and lens.

The binding of ten biotin-coupled lectins with different carbohydrate specificities to exfoliative material and neighbouring tissues was studied in 16 formalin-fixed and paraffin-embedded human eyes. Eight of the eyes were exfoliation positive while the rest were exfoliation negative. Exfoliative material reacted intensely with Lens culinaris (LCA), Canavalia ensiformis (ConA) and Ricinus communis (RCA-I) agglutinins. Positive reaction was also seen with wheat germ (WGA), peanut (PNA) and soybean (SBA) agglutinins. The superficial zonular lamella, zonular fibers and the non-pigmented epithelium of the ciliary body had a rather similar lectin-binding profile to exfoliative material. The lens capsule was essentially unreactive with all the lectins used. The lens epithelium reacted faintly with ConA, LCA, WGA and RCA-I. Pre-treatment with neuraminidase to remove sialic acid resulted in increased binding of PNA and SBA to exfoliative material, zonular fibers and the zonular lamella, and in decreased binding of WGA to the non-pigmented epithelium of the ciliary body, zonular fibers and the zonular lamella. The results indicate that alpha-mannosyl, beta-galactosyl, N-acetyl-D-glucosaminyl and N-acetylneuraminic acid residues are present in glycoconjugates of exfoliative material and neighbouring tissues.

Aged↗

PubMed1997

Lamina-specific connectivity in the brain: regulation by N-cadherin, neurotrophins, and glycoconjugates.

In the vertebrate brain, neurons grouped in parallel laminae receive distinct sets of synaptic inputs. In the avian optic tectum, arbors and synapses of most retinal axons are confined to 3 of 15 laminae. The adhesion molecule N-cadherin and cell surface glycoconjugates recognized by a plant lectin are selectively associated with these "retinorecipient" laminae. The lectin and a monoclonal antibody to N-cadherin perturbed laminar selectivity in distinct fashions. In contrast, neurotrophins increased the complexity of retinal arbors without affecting their laminar distribution. Thus, cell surface molecules and soluble trophic factors may collaborate to shape lamina-specific arbors in the brain, with the former predominantly affecting their position and the latter their size.

Animals↗

PubMed1992

Polymorphism of the 35- and 50-kilodalton surface glycoconjugates of Trypanosoma cruzi metacyclic trypomastigotes.

In this study, we examined the immunochemical properties of the 35- and 50-kDa (35/50-kDa) surface glycoconjugates expressed on the surface of metacyclic trypomastigotes of Trypanosoma cruzi using three different monoclonal antibodies directed to this component. The 35/50-kDa surface antigen was expressed by metacyclic trypomastigotes of 11 different strains of T. cruzi and displayed a significant degree of molecular polymorphism. Results of immunoblotting and complement-mediated lysis were consistent with such diversity. Different monoclonal antibodies reacted with distinct epitopes on the 35/50-kDa antigen, which is resistant to proteases and behaves as an amphiphilic component.

Animals↗

PubMed1992

Actinomyces tissue specificity may depend on differences in receptor specificity for GalNAc beta-containing glycoconjugates.

Actinomyces naeslundii 12104 and A. viscosus LY7 were compared for receptor specificities and adherence properties because these relate to their oral colonization sites. Both strains bind GalNAc beta-containing glycosphingolipids (GSLs) in a GalNAc beta 1-3Gal alpha Oethyl-sensitive fashion but differ with respect to the number of cells bound to GSLs and the effect of neighboring sugar groups on the binding. Their hemagglutination and saccharide inhibition profiles confirms the existence of two receptor specificities (for example, when GalNAc beta 1-3Gal alpha Oethyl is multivalently conjugated to albumin, its inhibitory activity increases fourfold toward strain 12104 but decreases fourfold toward strain LY7). Trypsin or chymotrypsin treatment of human erythrocytes, which possess receptor GSLs, improves their hemagglutination with strain 12104. In contrast, the same treatment of chicken erythrocytes, which lack receptor GSLs, abolishes their hemagglutination. These findings suggest that both GSLs and glycoproteins act as functional receptors on eukaryotic cells. The strains also differ with respect to the following GalNAc beta 1-3Gal alpha Oethyl-sensitive adherence properties: (i) strain LY7 adheres somewhat better than does strain 12104 to buccal epithelial cells; (ii) in spite of their similar overall coaggregation patterns with streptococci, strain 12104 coaggregates with Streptococcus oralis MPB1 but strain LY7 does not; (iii) strain 12104 alone shows GalNAc beta-sensitive saliva aggregation and adherence to saliva-coated hydroxyapatite. The GSL binding patterns of fresh Actinomyces isolates reveal a high prevalence of LY7-like specificities among buccal isolates, whereas 12104-like specificities are most prevalent among plaque isolates. These findings strongly suggest that fresh Actinomyces isolates use fine specificity for GalNAc beta-containing glycoconjugates in recognition and subsequent colonization of specific oral surfaces.

Acetylgalactosamine↗

PubMed1993

An artificial glycoconjugate containing the bisphosphorylated glucosamine disaccharide backbone of lipid A binds lipid A monoclonal antibodies.

Monoclonal antibodies (MAbs) against lipid A, the endotoxic component of lipopolysaccharide (LPS) of gram-negative bacteria, are presently discussed as therapeutic agents against lethal gram-negative infections; however, their binding specificities are controversial. We have isolated from the LPS of Escherichia coli J-5 the 1,4'-bisphosphorylated beta 1-->6-linked glucosamine disaccharide backbone of its lipid A moiety, which was covalently linked to bovine serum albumin. It was shown by solid-phase enzyme immunoassay that one antibody (MAb A6) bound equally well to the glycoconjugate and synthetic E. coli-type lipid A over a broad range of antigen concentrations whereas two other MAbs (IC3 and S1-15) bound better to the conjugate at low antigen concentrations and better to the lipid A when high concentrations of antigen were used. This proves in a direct way that there exist lipid A MAbs with different specificities which bind to epitopes in the hydrophilic backbone of lipid A and which do not require the presence of fatty acids.

Antibodies, Monoclonal↗

PubMed1991

Structure, serological specificity, and synthesis of artificial glycoconjugates representing the genus-specific lipopolysaccharide epitope of Chlamydia spp.

The human bacterial pathogens Chlamydia spp. possess a genus-specific lipopolysaccharide as a major surface antigen, the structure of which has been determined by analytical chemistry as Kdop alpha 2-8-Kdop alpha 2-4-Kdop alpha 2-6GlcNp beta 1-6-GlcNol (Kdo, 3-deoxy-D-manno-2-octulosonic acid). Immunochemical studies on this pentasaccharide and the chemically synthesized partial structures Kdop alpha 2-8-Kdop alpha 2-4-Kdop alpha 2-6GlcNp beta, Kdop alpha 2-8-Kdop alpha 2-4-Kdop alpha, Kdop alpha 2-4-Kdop alpha, Kdop alpha 2-8-Kdop alpha, and Kdop alpha using artificial glycoconjugate antigens and monoclonal antibodies showed that fatty acids and phosphoryl groups (as present in native lipopolysaccharide) are dispensable for constitution of the genus-specific epitope and that the minimal structure to exhibit chlamydia specificity is the Kdo trisaccharide moiety.

Antibodies, Bacterial↗

PubMed2003

The viral sigma1 protein and glycoconjugates containing alpha2-3-linked sialic acid are involved in type 1 reovirus adherence to M cell apical surfaces.

Type 1 reoviruses invade the intestinal mucosa of mice by adhering selectively to M cells in the follicle-associated epithelium and then exploiting M cell transport activity. The purpose of this study was to identify the apical cell membrane component and viral protein that mediate the M cell adherence of these viruses. Virions and infectious subviral particles of reovirus type 1 Lang (T1L) adhered to rabbit M cells in Peyer's patch mucosal explants and to tissue sections in an overlay assay. Viral adherence was abolished by pretreatment of sections with periodate and in the presence of excess sialic acid or lectins MAL-I and MAL-II (which recognize complex oligosaccharides containing sialic acid linked alpha2-3 to galactose). The binding of T1L particles to polarized human intestinal (Caco-2(BBe)) cell monolayers was correlated with the presence of MAL-I and MAL-II binding sites, blocked by excess MAL-I and -II, and abolished by neuraminidase treatment. Other type 1 reovirus isolates exhibited MAL-II-sensitive binding to rabbit M cells and polarized Caco-2(BBe) cells, but type 2 or type 3 isolates including type 3 Dearing (T3D) did not. In assays using T1L-T3D reassortants and recoated viral cores containing T1L, T3D, or no sigma1 protein, MAL-II-sensitive binding to rabbit M cells and polarized Caco-2(BBe) cells was consistently associated with the T1L sigma1. MAL-II-recognized oligosaccharide epitopes are not restricted to M cells in vivo, but MAL-II immobilized on virus-sized microparticles bound only to the follicle-associated epithelium and M cells. The results suggest that selective binding of type 1 reoviruses to M cells in vivo involves interaction of the type 1 sigma1 protein with glycoconjugates containing alpha2-3-linked sialic acid that are accessible to viral particles only on M cell apical surfaces.

Animals↗

PubMed1989

Evidence of altered structural and secretory glycoconjugates in the jejunal mucosa of patients with gluten sensitive enteropathy and subtotal villous atrophy.

The pattern of lectin histochemistry in formalin fixed, paraffin embedded normal jejunal and subtotal villous atrophy specimens from patients with gluten sensitive enteropathy were compared. There was no significant difference in the binding pattern of five lectins (Arachis hypogaea, Canavalia ensiformis, Lens culinaris, Phaseolus vulgaris and Triticum vulgaris) between normal and abnormal specimens. There were significant changes in the binding pattern of three lectins (Dolichos biflorus, Ulex europaeus, Ricinus communis), with special reference to goblet cells staining. These changes were present in all the specimens studied, regardless of the clinical diagnosis of dermatitis herpetiformis or coeliac disease. Dolichos biflorus reactive goblet cells were significantly decreased (p less than 0.001) in abnormal tissue and confined to the luminal edge of the mucosa. Strong reactivity of goblet cells in abnormal tissue was recorded with Ricinus communis and Ulex europaeus, lectins that bind to few or no goblet cells in normal tissue. These findings show that modifications of structural and secretory glycoconjugates occur in the jejunal mucosa of patients with gluten sensitive enteropathy.

Atrophy↗

PubMed1991

Inhibition of influenza A virus hemagglutinin and induction of interferon by synthetic sialylated glycoconjugates.

Multivalent forms of neoglycoproteins and polyacrylamides containing sialic acid were prepared and shown to be potent inhibitors of influenza A virus (H3N2) hemagglutinin with chick red blood cells. The synthetic sialylated glycoconjugates, although they were neuraminidase substrates, did not suppress viral neuraminidase and did not reduce infectivities in chick embryos. The copolyacrylamide conjugate containing a spacer group of approximately 11 A (1 A = 0.1 nm) between the polymer backbone and the sialic acid residues was the best hemagglutinin inhibitor. Moreover, it exhibited promising interferon-inducing properties.

Animals↗

PubMed2006

Effects of electroacupuncture with different frequencies on the glycoconjugate alterations in articular cartilage in the ankle joints of complete Freund's adjuvant-injected rats.

The aim of this study was to investigate the effects of electroacupuncture (EA) on the glycoconjugate (GC) changes in articular cartilage in the ankle of an arthritic model. Arthritis was induced by an intraplantar injection of complete Freund's adjuvant (CFA) into the hindpaw of male Sprague-Dawley rats. Bilateral EA stimulation at 2 Hz, 15 Hz and 120 Hz was applied at those acupoints corresponding to Zusanli and Sanyinjiao in man, using needles for 3-day intervals for 30 days. To determine the presence of arthritis, paw edema was measured by a water displacement plethysmometer. Edema of the hindpaw induced by CFA-injection was strongly inhibited by EA stimulation throughout the experimental period. At 30 days after CFA-injection, GC changes of articular cartilage of the ankle joint were observed using conventional and lectin histochemistry. The CFA-injected rat revealed general reduction of staining abilities and lectin affinities for GC in comparison with normal rats. Significant reductions of neutral and acidic GC were observed in interterritorial matrix and chondrocyte capsules, respectively. All lectin affinities examined except DBA were also decreased in CFA-injected rats compared to normal ones. However, EA-treated rats, showed similar staining patterns and lectin affinities for GC as to normal ones, especially neutral GC in interterritorial matrix and sWGA and RCA-1 affinities in chondrocytes. It is concluded that EA in all frequencies examined, especially 2 Hz, can attenuate inflammatory edema in CFA-injected rats through alleviation of alterations of GC components in articular cartilage.

Animals↗

PubMed1994

Regional differences in glycoconjugates of intestinal M cells in mice: potential targets for mucosal vaccines.

We have used a panel of lectins and antibodies to describe the composition of complex carbohydrates associated with M cells in various regions of the intestinal tract of adult BALB/c mice. The fucose-specific lectin Ulex europaeus agglutinin type I (UEA I) is a marker of M cells in the small intestine and recognized M cells at an early stage of differentiation. Subpopulations of M cells in a single follicle-associated epithelium (FAE) could be distinguished by different fucose-specific probes. Certain lectins revealed that M cells have basal processes that extend into the underlying lymphoid tissue. Colonic and rectal M cells display glycosylation patterns distinct from M cells of Peyer's patches and are characterized by terminal galactose. UEA I selectively adhered to Peyer's patch M cells in mucosal explants and in ligated intestinal loops in vivo. The lectin was taken up into endocytic vesicles and transported to the intra-epithelial pocket and other domains of the basolateral membrane. Thus M cell-specific glycoconjugates could serve as "receptors" for targeting of lectin-antigen conjugates to the mucosal immune system.

Animals↗

PubMed1990

Gastrin-releasing peptide stimulates glycoconjugate release from feline trachea.

The effect of gastrin-releasing peptide (GRP) on respiratory glycoconjugate (RGC) secretion was investigated in a feline tracheal organ culture model. RGC secretion was stimulated by GRP in a dose-dependent fashion at concentrations from 10(-8) to 10(-5) M (range 15-38% increase above control) with a peak effect within 0.5-1 h of incubation. GRP-(14-27), the receptor binding portion of GRP, and the related molecule, bombesin, also stimulated RGC secretion by approximately 20% above control. Acetyl-GRP-(20-27) stimulated RGC release by 10%, whereas GRP-(1-16) was inactive. Autoradiographic studies with 125I-GRP revealed that specific binding was restricted to the submucosal glands and the surface epithelium. A specific radioimmunoassay showed the content of GRP in feline trachea after extraction with ethanol-acetic acid to be 156 +/- 91 fmol/g wet wt. Indirect immunohistochemistry indicated that ganglion cells located just outside the cartilage contained GRP-immunoreactive materials. GRP is a novel mucus secretagogue that may participate in regulating airway mucosal gland secretion.

Animals↗

PubMed1997

Mucus glycoconjugate secretion in cool and hypertonic solutions.

For sensitive individuals, exercise-induced asthma is triggered by cold and dry air and is often accompanied by a productive cough. In this study, we determined whether cold solutions and/or solutions of increased tonicity directly caused an increase in glycoconjugate (GC) secretion. To test this, we used isolated swine tracheal submucosal gland cells (TSGCs) and measured the rate of GC secretion at 37 and 32 degrees C in isotonic solutions and in solutions made hypertonic by 30 mosM. TSGCs were isolated under conditions that minimized the rate of GC secretion and were perfused with medium 199 equilibrated with 5% CO2 to a pH of 7.4. A lectin-based assay was used to specifically detect GC present in each 2-min fraction of the perfusate. Basal secretion was 3.1-fold greater at 32 degrees C (n = 3) than at 37 degrees C (n = 4; P < 0.05). At 37 degrees C, increasing perfusate osmolarity by 30 mosM increased the average rate of secretion by 41 +/- 11% (n = 4; P < 0.05); return to isotonic perfusate caused a 4.5 +/- 1.8-fold transient increase in secretion (n = 4; P < 0.05) that was complete within 10 min. At 32 degrees C, changing tonicity of the perfusate had no significant effect but returning to isotonic perfusate caused a 2.3 +/- 0.7-fold transient increase in secretion (n = 3; P < 0.05). Thus key stimuli that trigger obstruction of airflow (cold and increased osmolarity) can also directly stimulate GC secretion in the airway. Such increased secretions may contribute to the productive cough observed in some individuals in response to cold air.

Animals↗

PubMed2000

Human neutrophil elastase releases two pools of mucinlike glycoconjugate from tracheal submucosal gland cells.

Neutrophil elastase can contribute to the pathogenesis of increased airway reactivity and excess mucus secretion in many pulmonary diseases. Ten nanomolar human neutrophil elastase (HNE) effectively empties airway serous cells, raising the question of why HNE is not equally effective at emptying mucous cells of their stored mucin because total release of mucin granules is not seen in postmortem examination of even the most severe disease. To better resolve the mucus secretagogue action of HNE, we measured secretion of mucinlike glycoconjugates (MGCs) released from freshly isolated swine tracheal submucosal gland cells in fractions of the superfusate acquired every 2 min. Six to fifty nanomolar HNE released a fixed quantity of MGCs at an increasing rate with increasing concentrations of enzyme, an action consistent with the release of cell surface mucinlike molecules. The polycation poly-L-lysine (1 microg/ml) released a similar transient of MGCs. A steady-state doubling of MGC rate of release was seen as long as 100 nM HNE was present, but this stimulus represented less than a 1% release of stored MGCs/min and was consistent with release of mucin vesicles from cell stores. Both actions of HNE were inhibited by the specific inhibitors L-680833 and DMP-777 but not by 30 microM erythromycin. Therefore, HNE release of MGCs from tracheal submucosal glands is limited by both the fixed quantity of the MGCs in the transient pool and by the small steady-state response to the higher concentrations of enzyme.

Animals↗