The structure of glycophorins of animal erythrocytes

The role of properdin and Factor H in disease

The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.

Hijacking Factor H for Complement Immune Evasion

The complement system is an essential player in innate and adaptive immunity. It consists of three pathways (alternative, classical, and lectin) that initiate either spontaneously (alternative) or in response to danger (all pathways). Complement leads to numerous outcomes detrimental to invaders, including direct killing by formation of the pore-forming membrane attack complex, recruitment of immune cells to sites of invasion, facilitation of phagocytosis, and enhancement of cellular immune responses. Pathogens must overcome the complement system to survive in the host. A common strategy used by pathogens to evade complement is hijacking host complement regulators. Complement regulators prevent attack of host cells and include a collection of membrane-bound and fluid phase proteins. Factor H (FH), a fluid phase complement regulatory protein, controls the alternative pathway (AP) both in the fluid phase of the human body and on cell surfaces. In order to prevent complement activation and amplification on host cells and tissues, FH recognizes host cell-specific polyanionic markers in combination with complement C3 fragments. FH suppresses AP complement-mediated attack by accelerating decay of convertases and by helping to inactivate C3 fragments on host cells. Pathogens, most of which do not have polyanionic markers, are not recognized by FH. Numerous pathogens, including certain bacteria, viruses, protozoa, helminths, and fungi, can recruit FH to protect themselves against host-mediated complement attack, using either specific receptors and/or molecular mimicry to appear more like a host cell. This review will explore pathogen complement evasion mechanisms involving FH recruitment with an emphasis on: (a) characterizing the structural properties and expression patterns of pathogen FH binding proteins, as well as other strategies used by pathogens to capture FH; (b) classifying domains of FH important in pathogen interaction; and (c) discussing existing and potential treatment strategies that target FH interactions with pathogens. Overall, many pathogens use FH to avoid complement attack and appreciating the commonalities across these diverse microorganisms deepens the understanding of complement in microbiology.

A Comprehensive Review of Our Current Understanding of Red Blood Cell (RBC) Glycoproteins

Human red blood cells (RBC), which are the cells most commonly used in the study of biological membranes, have some glycoproteins in their cell membrane. These membrane proteins are band 3 and glycophorins A-D, and some substoichiometric glycoproteins (e.g., CD44, CD47, Lu, Kell, Duffy). The oligosaccharide that band 3 contains has one N-linked oligosaccharide, and glycophorins possess mostly O-linked oligosaccharides. The end of the O-linked oligosaccharide is linked to sialic acid. In humans, this sialic acid is N-acetylneuraminic acid (NeuAc). Another sialic acid, N-glycolylneuraminic acid (NeuGc) is present in red blood cells of non-human origin. While the biological function of band 3 is well known as an anion exchanger, it has been suggested that the oligosaccharide of band 3 does not affect the anion transport function. Although band 3 has been studied in detail, the physiological functions of glycophorins remain unclear. This review mainly describes the sialo-oligosaccharide structures of band 3 and glycophorins, followed by a discussion of the physiological functions that have been reported in the literature to date. Moreover, other glycoproteins in red blood cell membranes of non-human origin are described, and the physiological function of glycophorin in carp red blood cell membranes is discussed with respect to its bacteriostatic activity.

Structure of a sialo-oligosaccharide from glycophorin in carp red blood cell membranes

We isolated a high-purity carp glycophorin from carp erythrocyte membranes and prepared the oligosaccharide fraction from glycophorin by β-elimination [1]. The oligosaccharide fraction was separated into two components (P-1 and P-2) using a Glyco-Pak DEAE column. These O-linked oligosaccharides (P-1 and P-2) were composed of glucose, galactose, fucose, N-acetylgalactosamine and N-glycolylneuraminic acid (NeuGc). The P-1 and P-2 contained one and two NeuGc residues, respectively, and the P-1 exhibited bacteriostatic activity [1]. Using NMR and GC-MS, we determined that the structure of the bacteriostatic P-1 was NeuGcα2→6 (Fucα1→4) (Glcα1→3) Galβ1→4GalNAc-ol. This O-linked oligosaccharide was unique for a vertebrate with respect to the hexosamine and hexose linkages and its non-chain structure.

Histoplasma capsulatum yeast cells attach and agglutinate human erythrocytes

The ability of yeast cells of Histoplasma capsulatum to attach and agglutinate human erythrocytes has been described. This is the first report involving these yeasts in the hemagglutination phenomenon. Results revealed that the yeast cells were able to bind to erythrocytes irrespective of blood groups and to agglutinate them when a high density of yeast cells was used. Assays on the inhibition of yeast attachment to erythrocytes were also performed, using sugar-treated yeast cells. Results indicate that galactose (Gal), mainly the beta-anomer, specially inhibited yeast attachment. Disaccharides (Gal-derivatives) and glycosaminoglycans containing Gal residues, mainly chondroitin sulfate C, promote this type of inhibition. In addition, preliminary data of inhibition assays also involved a probable ionic strength driven mechanism mediated by sialic acid and heparan sulfate, suggesting that yeast binding to erythrocytes could be associated with negative charges of both molecules.

Structure of a neutral glycosphingolipid recognized by human antibodies in polyagglutinable erythrocytes from the rare NOR phenotype

NOR is a rare inheritable polyagglutination phenomenon that has been described in two families. Our recent studies on these erythrocytes showed they contained at least two unique neutral glycosphingolipids, and based on their reactivity with Griffonia simplicifolia IB4 (GSL-IB4) isolectin (Kusnierz-Alejska, G., Duk, M., Storry, J. R., Reid, M. E., Wiecek, B., Seyfried, H., and Lisowska, E. (1999) Transfusion 39, 32-38), both oligosaccharide chains terminated with an alpha-galactose residue. The reactivity with GSL-IB4 suggested that these oligosaccharide chains terminated with a Galalpha1-->3Gal- sequence and that anti-NOR agglutinins were common human anti-Galalpha1-->3Gal xenoantibodies. In this report we describe the structure of one NOR component (NOR1) that migrated on thin-layer chromatographic plates in the region of pentaglycosylceramides. Treatment of this sample with alpha-galactosidase and beta-N-acetylhexosaminidase was followed by high-performance thin-layer chromatography with product detection by lectins and the anti-Gb4 monoclonal antibody. The results suggested that NOR1 was an alpha-galactosylated Gb4Cer with a beta-N-acetylhexosaminidase-resistant GalNAc residue. Gas phase disassembly by ion trap mass spectrometry analysis showed the sequence to be Hex1-->4HexN1-->3Hex1-->4Hex1-->4Hex linked to a ceramide composed of C18 sphingosine and a C24 monounsaturated fatty acid. Together these data indicate NOR1 to be a novel Galalpha1-->4GalNAcbeta1-->3Galalpha1-->4Galbeta1-->4 Glc-Cer structure. Additionally it has been shown that NOR glycolipids are recognized by human antibodies that were distinct from the known anti-Galalpha1-->3Gal xenoantibodies.

Hemagglutinin residues of recent human A(H3N2) influenza viruses that contribute to the inability to agglutinate chicken erythrocytes

To identify the molecular determinants contributing to the inability of recent human influenza A(H3N2) viruses to agglutinate chicken erythrocytes, phenotypic revertants were selected upon passage in eggs or MDCK cells. The Leu194Ile or Val226Ile substitutions were detected in their hemagglutinin (HA) sequence concomitantly with the phenotypic reversion. Remarkably, as little as 3.5% of variants bearing a Val226Ile substitution was found to confer the ability to agglutinate chicken erythrocytes to the virus population. Hemadsorption assays following transient expression of mutated HA proteins showed that the successive Gln226 --> Leu --> Ile --> Val changes observed on natural isolates resulted in a progressive loss of the ability of the HA to bind chicken erythrocytes. The Val226Ile change maintained the preference of the HA for SAalpha2,6Gal over SAalpha2,3Gal and enhanced binding of the HA to alpha2,6Gal receptors present on chicken erythrocytes. In contrast, simultaneous Ser193Arg and Leu194Ile substitutions that were found to confer the ability to agglutinate sheep erythrocytes increased the affinity of the HA for SAalpha2,3Gal.

Antigenic Properties of Human Glycophorins - An Update

Glycophorins are complex heavily glycosylated antigens carrying peptidic and glycopeptidic epitopes. Detailed immunochemical studies showed that GPA/GPB and GPC/GPD molecules have defined sites which are particularly immunogenic. These sites include N-terminal portions of all glycophorins, internal fragments of their extracellular domains, and cytoplasmic tails. The extracellular epitopes involve directly oligosaccharide chains (e.g. blood group M- and N-related epitopes, or N-terminal epitopes of GPC) or have peptidic character, shown by the reaction of respective antibodies with synthetic peptides. Peptidic eitopes are independent of glycosylation, or are variably affected by adjacent O-glycans which may mask the epitopes or may be required for a proper exposure of an antibody binding site. Several low incidence epitopes are present on variant glycophorin molecules. Among anti-glycophorin antibodies there are the 'bispecific' ones, or antibodies recognizing an epitope formed by an interaction of two proteins (Wr(b)). Alltogether, the glycophorins serve as convenient model antigens for studying Ag-Ab interaction and a role of O-glycosylation in protein antigenic properties. Moreover, well defined specificty of monoclonal anti-glycophorin antibodies makes them more precise tools in serological investigation and identification of normal and variant antigens. Last but not least, elucidation of antigenic properties of glycophorins is important for identification and characterization of human anti-glycophorin antibodies, which in some cases create medical problems at transfusion or pregnancy.

Isolation and characterization of glycophorin from nucleated (chicken) erythrocytes

A sialoglycoprotein fraction was isolated from chicken erythrocytes by two methods based on the phenol extraction or chloroform/2-propanol extraction of differently prepared erythrocyte membranes. Both preparations gave in SDS-PAGE two major PAS-stained bands (GP2 and GP3), which migrated as 60- and 33-kDa species, respectively, compared to reference proteins, or as 44- and 23-kDa molecules, compared to human glycophorins. Some less abundant slower migrating PAS-stained components, antigenically related to GP2 and GP3, also were detected. No evidence for the presence of antigenically distinct glycoproteins of leukosialin type was obtained. Interconversion in SDS-PAGE, similar carbohydrate composition, and similar antigenic properties of GP2 and GP3 indicated that they are a dimer and monomer, respectively, of the same glycoprotein which shows properties that allow it to be classified as a glycophorin. Lectin binding studies and methylation analysis of beta-elimination products of chicken glycophorin preparation showed the presence of O-glycans and N-glycans. The major O-glycans include sialylated Galbeta1-3GalNAc units and more complex GlcNAc-containing chains. Among the N-glycans, there are complex-type biantennary structures with a bisecting GlcNAc residue, accompanied by chains with additional antennas linked to alpha-mannose residues. A characteristic feature of the chicken glycophorin is a relatively high proportion of N-glycans to O-glycans, compared to the glycophorin A from human erythrocytes.

Lectin from Beauveria bassiana mycelium recognizes Thomsen-Friedenreich antigen and related structures

A lectin was isolated from the mycelium of the stationary growing enthomopathogenic fungus Beauveria bassiana by extraction, chromatography on QAE-Sephadex A-25, salt precipitation, and hydrophobic chromatography on Phenyl-Sepharose 4B. The Beauveria bassiana lectin (BBL) is a 15 kDa glycoprotein rich in hydrophobic amino acids, without detectable amount of methionine. It contains 12.6% of carbohydrates including galactose and mannose. Isoelectric point was found at pH 7.1. The lectin is stable between pH 6 and 11, and at temperature under 50 degrees C. The activity of the lectin was not dependent on with Ca++, Mn++, Mg++ cations and was apparently not blood group ABO specific. The hemagglutination caused by the lectin was inhibited by alpha lactose (Gal beta 1-->4 Glc alpha), but not by beta lactose (Gal beta 1-->4 Glc beta). In direct ELISA the BBL preferentially reacted with some glycoproteins carrying O-linked sugar structure Gal beta 1-->3 GalNAc: strongly with human glycophorin A and weaker with mouse glycophorin, fetuin, IgA, ovine submaxillary mucin. On the other hand BBL did not react in direct ELISA with N-glycoproteins (alpha 1-acid glycoprotein, haptoglobin, fibronectin), however, N-glycoproteins could act as inhibitors of lectin-glycophorin A interaction. We observed also weak interaction with asialo-Tamm-Horsfall N-glycoprotein having unusual large, branched N-glycans with outer GalNAc beta 1-->4Gal sequence. Moreover, the interaction of BBL with highly sialylated preparations of glycoproteins was weaker than with asialo forms. Presented results indicate that BBL exhibits sugar binding specificity towards glycotope corresponding to Thomsen-Friedenreich antigen and its related sequences: Gal beta 1-->3 GalNAc > Neu Ac alpha 2-3 Gal beta 1-->3 (Neu Ac alpha 2-6) GalNAc > Gal beta 1-->4 Glc alpha.

Characterization of glycoprotein glycan receptors for Escherichia coli F17 fimbrial lectin

The specificity of N-acetylglucosamine-binding F17 fimbrial lectin of coli (also called FY or Att25) for the oligosacharide structures was investigated by mannose-resistant hemagglutination inhibition tests and direct binding assays. The linkage position of N-acetyl-glucosamine influenced its affinity in the preferential order of beta 1-3 > beta 1-6 > beta 1-4 beta > beta 1-2. Minimal GlcNAc beta 1-3Gal beta 1-sequence strongly bound to F17 lectin, whether located in terminal nonreducing position or internally in carbohydrate moieties. F17 lectin specifically interacted with this unit in O-glycosidically linked oligosaccharides of the bovine glycophorins and intestinal mucins. On the contrary, GlcNAc beta 1-NAsn, GlcNAc beta 1-6Man beta- and GlcNAc beta 1-4GlcNAc- of N-glycosylated proteins failed to bind to the lectin. Our findings emphasized the presence of multiple F17 mucosal receptor complex in the newborn calf intestines. Furthermore, the density of receptors for F17 fimbrial lectin seemed to depend on the age of the calf and the intestinal segment.

Sialoadhesin, myelin-associated glycoprotein and CD22 define a new family of sialic acid-dependent adhesion molecules of the immunoglobulin superfamily

BACKGROUND

Protein-carbohydrate interactions are believed to be important in many biological processes that involve cell-cell communication. Apart from the selectins, the only well-characterized vertebrate sialic acid-dependent adhesion molecules are CD22 and sialoadhesin; CD22 is a member of the immunoglobulin superfamily that is expressed by B lymphocytes and sialoadhesin is a macrophage receptor. The recent cloning of the gene encoding sialoadhesin has shown that it is also immunoglobulin-like. Both proteins share sequence similarity with the myelin-associated glycoprotein, an adhesion molecule of oligodendrocytes and Schwann cells that has been implicated in the process of myelination, raising the important question of whether myelin-associated glycoprotein is also a sialic acid-binding protein.

RESULTS

We have investigated the binding properties of these three receptors when expressed either in monkey COS cells or as chimaeric proteins containing the Fc portion of human immunoglobulin G. We demonstrate that, like sialoadhesin and CD22, myelin-associated glycoprotein mediates cell adhesion by binding to cell-surface glycans that contain sialic acid. We have dissected the specificities of these three adhesins further: whereas sialoadhesin binds equally to the sugar moieties NeuAc alpha 2-->3Gal beta 1-->3(4)GlcNAc or NeuAc alpha 2-->3Gal beta 1-->3GalNAc, myelin-associated glycoprotein recognizes only NeuAc alpha 2-->3Gal beta 1-->3GalNAc and CD22 binds specifically to NeuAc alpha 2-->6Gal beta 1-->4GlcNAc. Furthermore, we show that the recognition of sialylated glycans on the surfaces of particular cell types leads to the selective binding of sialoadhesin to neutrophils, myelin-associated glycoprotein to neurons and CD22 to lymphocytes.

CONCLUSIONS

Our findings demonstrate that a subgroup of the immunoglobulin superfamily can mediate diverse biological processes through recognition of specific sialylated glycans on cell surfaces. We propose that this subgroup of proteins be called the sialoadhesin family.

Blood group antigens on human erythrocytes-distribution, structure and possible functions

Human erythrocyte blood group antigens can be broadly divided into carbohydrates and proteins. The carbohydrate-dependent antigens (e.g., ABH, Lewis, Ii, P1, P-related, T and Tn) are covalently attached to proteins and/or sphingolipids, which are also widely distributed in body fluids, normal tissues and tumors. Blood group gene-specific glycosyltransferase regulate the synthesis of these antigens. Protein-dependent blood group antigens (e.g., MNSs, Gerbich, Rh, Kell, Duffy and Cromer-related) are carried on proteins, glycoproteins and proteins with glycosylphosphatidylinositol anchor. The functions of these molecules on human erythrocytes remain unknown; some of them may be involved in maintaining the erythrocyte shape. This review describes the distribution, structures and probable biological functions of some of these antigens in normal and pathological conditions.

Immunological relationship among rat erythrocyte membrane sialoglycoproteins and with human glycophorins

1. Specific antibodies against a whole preparation of glycophorins from rat erythrocyte membrane and against its most prominent component (32 kDa) were prepared. 2. Both antisera and the respective affinity-purified antibodies recognize the 74, 32 and 25 kDa components of rat glycophorins; therefore, a close antigenic relationship between them can be inferred. 3. On the other hand, a cross-reaction with human glycophorin A (both MM- and NN-type) is observed for both antisera. 4. This suggests the existence of epitopes common to human and rat glycophorins.

Immunoanalysis and quantitation of membrane sialoglycoproteins (glycophorins) in rat erythrocytes and reticulocytes

An enzyme-linked immunosorbent assay (ELISA) for the quantitation of rat erythrocyte membrane sialoglycoproteins (glycophorins) has been developed. Samples of erythrocytes and reticulocytes were analysed using this assay, and response compared among them and purified glycophorins samples. A broadly homologous behaviour of glycophorins was found in both cell types, suggesting the presence in reticulocytes of glycophorin molecules closely similar to those on the erythrocyte. A quantitative evaluation of glycophorins on both cell types yielded comparable levels of these glycoproteins, but with significantly higher values (1.7-fold) for reticulocytes. It is suggested that the lower number of epitopes present on the erythrocyte membrane might be due to the disappearance of some glycophorin-associated antigenic determinants during the maturation of reticulocyte to erythrocyte.

Rat erythrocyte glycophorins can be isolated by the lithium diiodosalicylate method used for other glycophorins

1. The lithium diiodosalicylate/phenol method, widely employed for the isolation of membrane sialoglycoproteins (glycophorins) from mammalian erythrocytes, was applied for the first time to the purification of homologous glycoproteins from rat erythrocyte membranes. 2. The resulting preparations showed to be composed of four components, fractionated on SDS-PAGE. All four were positive for periodic acid-Schiff's reagent stain, the two largest of them being major. 3. Isolated rat glycophorins accounted for 60% of the ghost sialic acid and 1.5% of their protein. The presence of O-acetyl groups was confirmed in one-third of the sialic acid residues. 4. The molecular masses of the four glycophorin components were determined by a method which takes into account the anomalous mobility of glycoproteins on SDS-electrophoresis. Estimated values thus obtained for the actual molecular masses were 74, 32, 25 and 17 kDa.

Common peptide epitopes in glycophorin and the endothelial sialoglycoprotein gp60

Polyclonal anti-serum made against murine glycophorin gp3 (alpha gp) recognizes the endothelial albumin binding glycoprotein, gp60. In this study, we investigated the nature (peptide vs. carbohydrate) of the common epitope. First, a new technique was developed to remove oligosaccharides from glycoproteins that were first immobilized on filters and then subjected to beta-elimination. When greater than 90% of the glycans of gp60 were removed, alpha gp still recognized gp60 without apparent loss of affinity. Second, we used brefeldin A to accumulate unglycosylated glycophorin precursors in order to affinity-purify peptide-specific alpha gp immuno-globulins; these antibodies recognized gp60. Finally, alpha gp recognized from in vitro translations a 48 kDa putative polypeptide precursor of gp60. These different approaches indicate that gp60 and gp3 have at least one common epitope in their peptide backbones.

Application of chemically desialylated and degalactosylated human glycophorin for induction and characterization of anti-Tn monoclonal antibodies

Human erythrocyte glycophorin was desialylated by mild acid hydrolysis and degalactosylated by Smith degradation. Two monoclonal antibodies (Tn5 and Tn56) obtained by immunization of mice with this 'artificial' Tn antigen were characterized and compared in some experiments with two antibodies (BRIC111 and LM225) obtained in other laboratories by immunization with Tn erythrocytes. The specific binding of the antibodies to glycophorins desialylated and degalactosylated on the nitrocellulose blot and to asialo-agalactoglycophorin-coated ELISA plates, and reactions with authentic Tn antigen served for identification of their anti-Tn specificity. The antibodies were further characterized in inhibition assay with various glycoproteins. The antibody Tn5 (similar to BRIC111) was shown to be specific for human erythrocyte Tn antigen, whereas Tn56 reacted strongly with different glycoproteins carrying O-linked GalNAc alpha- residues, and was strongly bound to the murine adenocarcinoma cell line Ta3-Ha. The antibodies Tn5, Tn56 and BRIC111 were similarly inhibited by ovine submaxillary mucin (OSM) and asialoOSM, but the antibody LM225 showed a distinct preference in reaction with OSM (sialosyl-Tn antigen). The results show that Tn antigen, obtained by chemical modifications of human glycophorin, enables the preparation and characterization of anti-Tn monoclonal antibodies, without using rare Tn erythrocytes.

Human erythrocyte glycophorins: protein and gene structure analyses

Human RBCs glycophorins are integral membrane proteins rich in sialic acids that carry blood group antigenic determinants and serve as ligands for viruses, bacteria, and parasites. These molecules have long been used as a general model of membrane proteins and as markers to study normal and pathological differentiation of the erythroid tissue. The RBC glycophorins known as GPA, GPB, GPC, GPD, and GPE have recently been fully characterized at both the protein and the DNA levels, and these studies have demonstrated conclusively that these molecules can be subdivided into two groups that are distinguished by distinct properties. The first group includes the major proteins GPA and GPB, which carry the MN and Ss blood group antigens, respectively, and a recently characterized protein, GPE, presumably expressed at a low level on RBCs. All three proteins are structurally homologous and are essentially erythroid specific. The respective genes are also strikingly homologous up to a transition site defined by an Alu repeat sequence located about 1 Kb downstream from the exon encoding the transmembrane regions. Downstream of the transition site, the GPB and GPE sequences are still homologous, but diverge completely from those of GPA. The three glycophorin genes are organized in tandem on chromosome 4q28-q31, and define a small gene cluster that presumably evolved by duplication from a common ancestral gene. Most likely two sequential duplications occurred, the first, about 9 to 35 million years ago, generated a direct precursor of the GPA gene, and the second, about 5 to 21 million years ago, generated the GPB and GPE genes and that involved a gene that acquired its specific 3' end by homologous recombination through Alu repeats. Numerous variants of GPA and GPB usually detected by abnormal expression of the blood group MNSs antigens are known. An increasing number of these variants have been structurally defined by protein and molecular genetic analyses, and have been shown to result from point mutations, gene deletions, hybrid gene fusion products generated by unequal crossing-over (not at Alu repeats), and microconversion events. The second group of RBC membrane glycophorins includes the minor proteins GPC and GPD both of which carry blood group Gerbich antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region, and that both proteins are produced by a unique gene called GE (Gerbich), which is present as a single copy per haploid genome and is located on chromosome 2q14-q21.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural analysis of the N-linked oligosaccharides from murine glycophorin

Glycophorins, isolated from BALB/c mouse erythrocytes, were degraded under mild and strong reductive alkaline conditions and the N-linked oligosaccharides were isolated as alditols. The oligosaccharide alditols were fractionated and purified using gel filtration, concanavalin A-Sepharose affinity chromatography, and high-performance ion-exchange chromatography. Structural analysis was carried out by chemical analyses, periodate oxidation in combination with fast atom bombardment mass spectrometry, and 500-MHz 1H NMR spectroscopy. The results revealed the presence of sialylated biantennary, triantennary, and tetraantennary complex type oligosaccharides, all fucosylated at the innermost N-acetylglucosamine residue. The tri- and tetraantennary oligosaccharide-containing fractions also contained species elongated by one and/or two N-acetyllactosamine (-3Gal beta 1-4GlcNAc beta 1-) sequences. The N-linked oligosaccharides were shown to be combined only with one (the low molecular weight) of the two mouse glycophorins.

Swine and cattle enterotoxigenic Escherichia coli-mediated diarrhea. Development of therapies based on inhibition of bacteria-host interactions

Enterotoxigenic Escherichia coli (ETEC) frequently occurs in diarrheal disease afflicting domestic animals. In this paper is summarized the research carried out over the last decade on the two important determinants of virulence that plays a role in the development of the infection, namely the colonizing ability of the small intestine mediated by specific fimbrial adhesins acting as lectins and the production of enterotoxins. Recent progress in knowledge of the phenomenon led to alternative strategies of prevention and cure of enteric infection. Since bacterial recognition of mucosa surface receptors in an initial event in colonization, several approaches based on the competitive inhibition of ETEC adhesion have been developed. This review examines the following approaches: competitive colonization with non pathogenic strains, design of adhesin or toxin vaccines, receptor analog therapy and methods for in vivo suppression of virulence factors.

Structure of the major O-glycosidic oligosaccharide of monkey erythrocyte glycophorin

Sialic acids and the major O-glycosidic oligosaccharide of glycophorin MK from monkey (Japanese monkey, Macaca fuscata) erythrocyte membranes were characterized. N-Glycolylneuraminic acid (Neu5Gc) was found as the major sialic acid, which was confirmed by gas-liquid chromatography-mass spectrometry as the trimethylsilyl methyl ester. Three O-glycosidic oligosaccharide units were obtained from a tryptic glycopeptide that contained all of the carbohydrate units in glycophorin MK by mild alkaline borohydride/borotritide treatment. Carbohydrate analyses of the oligosaccharides revealed that they were composed of Neu5Gc, galactose and N-acetylgalactosaminitol in the molar ratios of 1:1:1 (trisaccharide), 2:1:1 (tetrasaccharide) and 3:1:1 (pentasaccharide). The content of oligosaccharide units was estimated to be 1:12:5 for penta-, tetra- and trisaccharide, respectively, based on the yields, the molecular weight, and the number of oligosaccharide attachment sites in the amino-acid sequence. The tetrasaccharide was the major oligosaccharide and its structure was proposed to be Neu5Gc alpha 2-3Gal beta 1-3[Neu5Gc alpha 2-6]GalNAcol.

Structural analysis by fast-atom-bombardment mass spectrometry of the mixture of alditols derived from the O-linked oligosaccharides of murine glycophorins

The O-glycosylically linked oligosaccharides from glycophorins of BALB/c mouse erythrocytes were released as a mixture of alditol derivatives on reductive beta-elimination. A new approach, based on periodate oxidation in combination with f.a.b.-m.s., was used to elucidate the structure of one of the branched derivatives in the mixture. Evidence for the anomeric configuration was obtained by 500-MHz 1H-n.m.r. spectroscopy. The following structures were found: (Formula: see text).