The sialoglycoproteins of murine erythrocyte ghosts. A modified periodic acid-Schiff stain procedure staining nonsubstituted and O-acetylated sialyl residues on glycopeptides

Antimicrobial, anti-inflammatory and anti-arthritic activity of hemolymph lectin (NagLec) isolated from the freshwater crab, Oziotelphusanaga

Lectins are non-immune glycoproteins or proteins having a unique capacity to interact with carbohydrate ligands found on the surface of their host cells. In the present investigation, the lectin was purified from the hemolymph of freshwater crab, Oziotelphusa naga and its antimicrobial, anti-inflammatory and anti-arthritic activity was analysed. The preliminary characterization of the hemagglutinin was carried out to identify the erythrocyte and sugar specificity, optimum pH and temperature and cation dependency. The agglutinin was found to be highly specific to rabbit erythrocyte and inhibited by fetuin and α-lactose. Maximum hemagglutination activity was noted at pH 7.5-8 and temperature 20-40 °C. An O-acetyl sialic acid specific 75 kDa hemolymph lectin, designated as NagLec was isolated from the freshwater crab, Oziotelphusa naga by affinity chromatography on fetuin coupled Sepharose 4 B, with a purification fold of 185. The bacteria Staphylococcus aureus, Proteus mirabilis and fungus Candida albicans had the greatest zone of inhibition when treated with NagLec. The results of the Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) assays showed that the purified lectin inhibited the growth of Staphylococcus aureus at 0.031 and 0.065 μg/ml, which proved the bactericidal property of NagLec. NagLec generated alterations on the bacterial cells and led to protein leakage, which was dosage (24 and 48 μg/ml) and time dependent (10-40 min). COX and LOX enzyme was inhibited to 49.43% and 61.81% with 100 μg/ml concentration of NagLec respectively, demonstrating NagLec's ability to reduce inflammation. Furthermore, NagLec (500 μg) suppressed protein denaturation up to 77.12% whereas diclofenac sodium (a standard drug) was inhibited by 89.36%. The results indicate that NagLec, a sialic acid specific lectin isolated from the freshwater crab O. naga could be formulated as a nano drug in future owing to its antimicrobial, anti-inflammatory and anti-arthritic potential that could be targeted to specific pathogenic microbes and treat arthritis.

Post-Glycosylation Modification of Sialic Acid and Its Role in Virus Pathogenesis

Sialic acids are a family of nine carbon keto-aldononulosonic acids presented at the terminal ends of glycans on cellular membranes. α-Linked sialoglycoconjugates often undergo post-glycosylation modifications, among which O-acetylation of N-acetyl neuraminic acid (Neu5Ac) is the most common in mammalian cells. Isoforms of sialic acid are critical determinants of virus pathogenesis. To date, the focus of viral receptor-mediated attachment has been on Neu5Ac. O-Acetylated Neu5Acs have been largely ignored as receptor determinants of virus pathogenesis, although it is ubiquitous across species. Significantly, the array of structures resulting from site-specific O-acetylation by sialic acid O-acetyltransferases (SOATs) provides a means to examine specificity of viral binding to host cells. Specifically, C₄ O-acetylated Neu5Ac can influence virus pathogenicity. However, the biological implications of only O-acetylated Neu5Ac at C_7-9 have been explored extensively. This review will highlight the biological significance, extraction methods, and synthetic modifications of C₄ O-acetylated Neu5Ac that may provide value in therapeutic developments and targets to prevent virus related diseases.

Murine Red Blood Cells Lack Ligands for B Cell Siglecs, Allowing Strong Activation by Erythrocyte Surface Antigens

CD22 and sialic acid-binding Ig-like lectin (Siglec)-G are members of the Siglec family of inhibitory coreceptors expressed on B cells that participate in enforcement of peripheral B cell tolerance. We have shown previously that when a BCR engages its cognate Ag on a cell surface that also expresses Siglec ligands, B cell Siglecs are recruited to the immunological synapse, resulting in suppression of BCR signaling and B cell apoptosis. Because all cells display sialic acids, and CD22 and Siglec-G have distinct, yet overlapping, specificities for sialic acid-containing glycan ligands, any cell could, in principle, invoke this tolerogenic mechanism for cell surface Ags. However, we show in this article that C57BL/6J mouse RBCs are essentially devoid of CD22 and Siglec-G ligands. As a consequence, RBCs that display a cell surface Ag, membrane-bound hen egg lysozyme, strongly activate Ag-specific B cells. We reasoned that de novo introduction of CD22 ligands in RBCs should abolish B cell activation toward its cognate Ag on the surface of RBCs. Accordingly, we used a glyco-engineering approach wherein synthetic CD22 ligands linked to lipids are inserted into the membrane of RBCs. Indeed, insertion of CD22 ligands into the RBC cell surface strongly inhibited B cell activation, cytokine secretion, and proliferation. These results demonstrate that the lack of Siglec ligands on the surface of murine RBCs permits B cell responses to erythrocyte Ags and show that Siglec-mediated B cell tolerance is restricted to cell types that express glycan ligands for the B cell Siglecs.

A mushroom lectin from ascomycete Cordyceps militaris

A mushroom lectin has been purified from ascomycete Cordyceps militaris, which is one of the most popular mushrooms in eastern Asia used as a nutraceutical and in traditional Chinese medicine. This lectin, designated CML, exhibited hemagglutination activity in mouse and rat erythrocytes, but not in human ABO erythrocytes. SDS-PAGE of CML revealed a single band with a molecular mass of 31.0 kDa under both nonreducing and reducing conditions that was stained by silver nitrate, and a 31.4 kDa peak in a Superdex-200 HR gel-filtration column. The hemagglutination activity was inhibited by sialoglycoproteins, but not in by mono- or disaccharides, asialoglycoproteins, or de-O-acetylated glycoprotein. The activity was maximal at pH 6.0-9.1 and at temperatures below 50 degrees C. Circular dichroism spectrum analysis revealed that CML comprises 27% alpha-helix, 12% beta-sheets, 29% beta-turns, and 32% random coils. Its binding specificity and secondary structure are similar to those of a fungal lectin from Arthrobotrys oligospora. However, the N-terminal amino acid sequence of CML differs greatly from those of other lectins. CML exhibits mitogenic activity against mouse splenocytes.

Purification, characterization, and sugar binding specificity of an N-Glycolylneuraminic acid-specific lectin from the mushroom Chlorophyllum molybdites

A carbohydrate-binding protein was isolated from the carpophores of the mushrooms and designated the Chlorophyllum molybdites lectin (CML) based on its origin. The molecular mass of CML was 32 kDa, and it was composed of two 16-kDa monomers with no disulfide bonds. Monosaccharide analysis indicated that 12% of the mass of CML was carbohydrate and consisted of GlcNAc:GalNAc:Gal:Man:l-Fuc in a molar ratio of 1.5:1.9: 4.4:4.8:1.0. In the hemagglutination inhibition assay, CML exhibited the strongest binding specificity toward N-glycolylneuraminic acid (NeuGc) among the monosaccharides tested, whereas NeuAc did not inhibit the hemagglutination at all. GalNAc and Mealpha-GalNAc were also inhibitory at much higher concentrations than NeuGc. Among the glycoproteins, asialobovine submaxillary mucin (BSM) and porcine stomach mucin (PSM) showed strong inhibitory effects. In surface plasmon resonance analysis, asialo-BSM and PSM exhibited the strongest binding affinity. After co-injection of CML and NeuGc or GalNAc onto the asialo-BSM- or PSM-immobilized chip, the dissociation of CML from the immobilized PSM was accelerated by NeuGc and GalNAc, but the dissociation of CML from the immobilized asialo-BSM was only promoted by GalNAc. These results and the other surface plasmon resonance experiments allowed us to conclude that the binding of asialo-BSM to CML was because of an interaction between the lectin and the GalNAc residues of asialo-BSM, and both the NeuGc and GalNAc residues were responsible for the binding of PSM to CML. The results also suggested that CML had two different carbohydrate binding domains, one specific for NeuGc and the other for GalNAc.

Purification and characterization of a sialic acid specific lectin from the hemolymph of the freshwater crab Paratelphusa jacquemontii

A naturally occurring hemagglutinin was detected in the serum of the freshwater crab, Paratelphusa jacquemontii (Rathbun). Hemagglutination activity with different mammalian erythrocytes suggested a strong affinity of the serum agglutinin for horse and rabbit erythrocytes. The most potent inhibitor of hemagglutination proved to be bovine submaxillary mucin. The lectin was purified by affinity chromatography using bovine submaxillary mucin-coupled agarose. The molecular mass of the purified lectin was 34 kDa as determined by SDS/PAGE. The hemagglutination of purified lectin was inhibited by N-acetylneuraminic acid but not by N-glycolylneuraminic acid, even at a concentration of 100 mm. Bovine submaxillary mucin, which contains mainly 9-O-acetyl- and 8,9 di-O-acety-N-acetyl neuraminic acid was the most potent inhibitor of the lectin. Sialidase treatment and de-O-acetylation of bovine submaxillary mucin abolished its inhibitory capacity completely. Also, asialo-rabbit erythrocytes lost there binding specificity towards the lectin. The findings indicated an O-acetyl neuraminic acid specificity of the lectin.

Characterization and partial purification of a lectin from the hemolymph of the white shrimp Litopenaeus schmitti

The agglutinating activity of the hemolymph of Litopenaeus schmitti is insensitive to calcium and specific for acetylated sugars, particularly sialic acid (Neu5Ac) and O-sialoglycoconjugates (bovine submaxillary mucin) and has varying specificity for different LPS, which may suggest a putative role in microorganism recognition. Affinity chromatography on fetuin-agarose of the agglutinin resulted in a 220 kDa band (lectin), and a 82.5 kDa band, which probably is hemocyanin. The 220 kDa protein consists of 31 and 34 kDa subunits, suggesting that this lectin is multimeric. The lectin molecular mass was estimated by gel filtration to be 153+/-10 kDa. The hemolymph of L. schmitti comprises at least another soluble lectin, with distinct chemical and carbohydrate specificity than the 220 kDa lectin.

Isolation and characterization of an acetyl group-recognizing agglutinin from the serum of the Indian white shrimp Fenneropenaeus indicus

A natural agglutinin from the serum of the Indian white shrimp Fenneropenaeus (Penaeus) indicus was purified to electrophoretic homogeneity by a single-step affinity chromatography on N-acetylglucosamine-Sepharose 6B. The expression of hemagglutinating (HA) activity of F. indicus agglutinin (FIA) was independent of the presence of divalent cations and insensitive to their chelators. FIA gave a single symmetrical peak in its native form with a molecular mass estimate of 200 kDa on gel filtration in HPLC, and SDS-PAGE under reducing conditions revealed that it is a homo-oligomer of a 27-kDa subunit protein. The pattern of reactivity of FIA against anti-FIA rabbit serum in immunodiffusion and immunoelectrophoretic analysis provided additional evidence for its purity and homogeneity. HA-inhibition studies documented exclusive specificity of FIA for acetyl groups in carbohydrates independently of the presence of these groups at the C-2 or C-5 position and its stereochemical arrangement in the axial or equatorial orientation. The unique ability of FIA to recognize acetyl groups was also explicitly demonstrated with sialo- and asialo-glycoproteins. Strikingly, FIA also interacted equally with amino acids and chemicals containing acetyl groups, thereby unambiguously demonstrating the exquisite specificity of FIA for an acetyl group, irrespective of the presence of this group in carbohydrate or noncarbohydrate ligands. The susceptibility of HA activity of FIA to inhibition by lipopolysaccharides from diverse gram-negative bacteria as well as its ability to selectively agglutinate several bacterial species isolated from infected shrimps implicate a potential role of this humoral agglutinin of F. indicus in the host immunodefense reactions against microbial invaders.

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.

Human recombinant interferon-inducible protein-10: intact disulfide bridges are not required for inhibition of hematopoietic progenitors and chemotaxis of T lymphocytes and monocytes

Human recombinant interferon-inducible protein-10 (rIP-10), a C-X-C chemokine, inhibits proliferation of human hematopoietic progenitors responsive to co-stimulation by recombinant steel factor (rSLF), is chemotactic for human monocytes and T-lymphocytes, and promotes T-lymphocyte adhesion to endothelial cells. Because chemokines have four conserved cysteines forming two intramolecular disulfide bridges, we decided to investigate their contribution in the biological activity of rIP-10. Since amino acid residues 22-98 of the sequence predicted by the cDNA constitute the naturally occurring IP-10, they were cloned after an initiating methionine into expression vector pET-3d. Subsequently rIP-10 was purified by enzymatic cell lysis, solubilization of refractile bodies with guanidine hydrochloride, renaturation by dialysis against dilute acetic acid, and sequential ion-exchange and reverse-phase high-performance liquid chromatography. Purified rIP-10 was reduced with 20 mM dithiothreitol, and chemically modified with 100 mM iodoacetamide (IAA), or S-methyl-methanethiosulfonate (MMTS), or N-methylmaleimide (NMM). Radiolabeling experiments demonstrated that 95% of the rIP-10 thiols were modified, and this was confirmed with SDS-PAGE. The biological activity of modified rIP-10 was determined in vitro by inhibition of rSLF-responsive human bone marrow hematopoietic progenitor proliferation and by chemotaxis assays using human T-lymphocytes and monocytes. In both assay systems, the biological activity was evident at rIP-10 concentrations of 20-100 ng/ml. The activity was preserved after modification of rIP-10 by IAA or MMTS, but was abolished after modification by NMM. We conclude that disulfide bridges are not essential for the biological activity of rIP-10.

Purification and characterization of a natural agglutinin from the serum of the hermit crab Diogenes affinis

A natural agglutinin from the serum of the hermit crab Diogenes affinis was purified to homogeneity by a single-step affinity chromatography using N-acetylglucosamine-coupled Sepharose 6B. The purified serum agglutinin (PSA) showed a strong affinity for rat RBC, and its hemagglutinating (HA) activity was specifically dependent on Ca2+ and reversibly sensitive to EDTA. PSA in active form has a molecular mass estimate of 185 kDa and is composed of four non-identical subunits (51, 49, 42 and 39 kDa) cross-linked by interchain disulfide bonds. The homogeneity of PSA was corroborated by immunodiffusion and immunoelectrophoretic analyses using rabbit antiserum raised against the agglutinin. The antibodies in this antiserum appear to be specific for RBC-binding sites of the agglutinin molecules as revealed by the ability of the antiserum to neutralize HA activities of both whole serum and PSA of D. affinis. In HA-inhibition assays performed with several carbohydrates and glycoproteins, PSA showed a distinct and unique specificity for acetyl group in carbohydrates independently of the presence of this group on C-2 or C-5 and its stereochemical arrangement in the axial or equatorial orientation. Besides, this agglutinin appears to recognize the terminal N- and O- acetyl groups in the oligosaccharide chain of glycoconjugates. The HA activity of D. affinis agglutinin was also susceptible to inhibition by lipopolysaccharides from diverse gram-negative bacteria, which might indicate a significant in vivo role of this humoral agglutinin in the host immune response against bacterial infections.

Regulation of sialic acid 9-O-acetylation during the growth and differentiation of murine erythroleukemia cells

Sialic acids are typically found at the terminal position on vertebrate oligosaccharides. They are sometimes modified by an O-acetyl ester at the 9-position, potentially altering recognition of sialic acid by antibodies, lectins, and viruses. 9-O-Acetylation is known to be selectively expressed on gangliosides in melanoma cells and on N-linked chains in hepatocytes. Using a recently developed probe, we show here that in murine erythroleukemia cells, this modification is selectively expressed on another class of oligosaccharides, O-linked chains carried on cell surface sialomucins. These cells also express 9-O-acetylation on the ganglioside GD3, but this modification appears to be undetectable on the cell surface. Increasing cell density in culture is associated with a decrease in cell surface 9-O-acetylation of sialomucins. This change correlates with the spontaneous differentiation toward a mature erythroid phenotype. This down-regulation upon differentiation and entry into the G0/G1 stage of the cell cycle is confirmed by differentiation-inducing agents. In contrast, cells arrested in G2/M by the microtubule depolymerizing agent nocodazole show increased expression of cell surface 9-O-acetylated sialomucins (but not the 9-O-acetylated ganglioside). However, the microtubule stabilizer taxol does not induce this increase, showing that the nocodazole effect is independent of cell cycle stage. Indeed, direct analysis showed no correlation of 9-O-acetylation with cell cycle stage in rapidly growing cells, and shorter treatments with nocodazole also increased expression. Western blots of cell extracts confirmed that changes caused by differentiation and nocodazole are not due to redistribution of molecules from the cell surface. Indeed, following selective removal of 9-O-acetyl groups from the cell surface by a specific esterase, the recovery of expression is mediated by new synthesis rather than by redistribution from an internal pool. Thus, 9-O-acetylation on these sialomucins appears to be primarily regulated by the rate of synthesis, and the increase with nocodazole treatment is likely due to the inhibition of turnover of cell surface molecules. These data show that 9-O-acetylation of sialic acids in murine erythroleukemia cells is a highly regulated modification, being selectively expressed in a cell type-specific manner on certain classes of oligosaccharides and differentially regulated with regard to subcellular localization and to the state of cellular differentiation.

Linkage-specific action of endogenous sialic acid O-acetyltransferase in Chinese hamster ovary cells

9-O-Acetylation of sialic acids shows cell type-specific and developmentally regulated expression in various systems. In a given cell type, O-acetylation can also be specific to a particular type of glycoconjugate. It is assumed that this regulation is achieved by control of expression of specific 9-O-acetyltransferases. However, it has been difficult to test this hypothesis, as these enzymes have so far proven intractable to purification or molecular cloning. During a cloning attempt, we discovered that while polyoma T antigen-positive Chinese hamster ovary cells (CHO-Tag cells) do not normally express cell-surface 9-O-acetylation, they do so when transiently transfected with a cDNA encoding the lactosamine-specific alpha2-6-sialyltransferase (Galbeta1-4GlcNAc:alpha2-6-sialyltransferase (ST6Gal I); formerly ST6N). This phenomenon is reproducible by stable expression of ST6Gal I in parental CHO cells, but not upon transfection of the competing lactosamine-specific alpha2-3-sialyltransferase (Galbeta1-(3)4GlcNAc:alpha2-3-sialyltransferase; (ST6Gal III) formerly ST3N) into either cell type. Further analyses of stably transfected parental CHO-K1 cells indicated that expression of the ST6Gal I gene causes selective 9-O-acetylation of alpha2-6-linked sialic acid residues on N-linked oligosaccharides. In a similar manner, while the alpha2-3-linked sialic acid residue of the endogenous GM3 ganglioside of CHO cells is not O-acetylated, transfection of an alpha2-8-sialyltransferase (GM3:alpha2-8-sialyltransferase (ST8Sia I); formerly GD3 synthase) caused expression of 9-O-acetylation of the alpha2-8-linked sialic acid residues of newly synthesized GD3. These data indicate either that linkage-specific sialic acid O-acetyltransferase(s) are constitutively expressed in CHO cells or that expression of these enzymes is secondarily induced upon expression of certain sialyltransferases. The former explanation is supported by a low level of background 9-O-acetylation found in parental CHO-K1 cells and by the finding that O-acetylation is not induced when the ST6Gal I or ST8Sia I cDNAs are overexpressed in SV40 T antigen-expressing primate (COS) cells. Taken together, these results indicate that expression of sialic acid 9-O-acetylation can be regulated by the action of specific sialyltransferases that alter the predominant linkage of the terminal sialic acids found on specific classes of glycoconjugates.

The specificity of the binding site of AchatininH, a sialic acid-binding lectin from Achatina fulica

A sialic acid-binding lectin, AchatininH (ATNH), having unique specificity towards 9-O-acetylneuraminic acid, has been purified and characterized. The specificity of this lectin for O-acetylsialic acids was studied in detail, using various sialic acid derivatives and sialoglycoproteins. The potent inhibition of hemagglutination by bovine submaxillary mucin (BSM), which contains 9(7,8)-O-acetylsialic acid and by free 9-O-acetylneuraminic acid confirms the preferential affinity towards this sugar. Further support for the role of O-acetylsialic acid was obtained by sialidase treatment of BSM. O-Deacetylation of the sialic acid residue abolished its inhibitory potency. Moreover, when the trihydroxypropyl side chain of the sialic acid molecule was modified by periodate-borohydride treatment, the truncated C7-sialic acid was unable to bind ATNH. This result suggests that the glycerol side chain of Neu5Ac, especially the C-8 and/or C-9 portion is an important determinant for ATNH. The hemagglutination-inhibition results using several mono-, di-, and tri-saccharides containing terminal sialic acid and various sialoglycoproteins reveals that ATNH preferentially binds the alpha-(2-->6)-linked sialic acid. Furthermore, beta-D-GlcNAc-(1-->3)-[alpha-NeuGc-(2-->6)]-GalNAc-ol was found to be the best ligand for ATNH.

O-acetylated sialic acid as a distinct marker for differentiation between several leukemia erythrocytes

AchatininH (ATNH) is a lectin, isolated from the hemolymph of Achatina fulica snail, which has been shown to have narrow specificity towards 9-O-acetyl sialic acid. Usually ATNH does not agglutinate normal human erythrocytes, however, it is capable of agglutinating erythrocytes of patients suffering from acute lymphocytic and acute myelogenous leukemia. Determination of binding constants, numbers of binding sites and lectin overlay experiments using patients' erythrocytes ghost, have suggested that some alterations in erythrocyte cell surface sialoglycoproteins or more precisely appearance of some O-acetylated sialoglycoprotein as a result of pathological transformations has caused this change in the binding of ATNH.

Hemagglutinating properties of enteroaggregative Escherichia coli

Many intestinal bacterial pathogens possess hemagglutinating properties, which are indicative of their adhesive properties to the intestinal mucosal surface. To understand the bacteria-mucosa interaction, 41 strains of enteroaggregative Escherichia coli (EAggEC), a recently described category of diarrheagenic E. coli, isolated mostly from children with diarrhea in Bangladesh, India, Thailand, Central America, and South America were screened for mannose-sensitive hemagglutination and mannose-resistant hemagglutination of erythrocytes from humans, rats, mice, sheep, cattle, and rabbits. Some strains demonstrated mannose-sensitive hemagglutination of erythrocytes. Most isolates showed mannose-resistant hemagglutination of erythrocytes from all species except rabbits. The hemagglutination patterns could be classified into 18 groups. Studies with three selected isolates suggested that hemagglutinins are cell bound and are protein in nature. On the basis of the pattern of inhibition of hemagglutination by various chemicals, 39 isolates were classified into 19 groups. Hemagglutinations of many isolates were inhibited by sialic acid-containing compounds, suggesting that these compounds may be the receptors for these organisms on erythrocytes and possibly on the intestinal mucosa. These data indicate that strains of EAggEC are a heterogeneous group of organisms with different types of hemagglutinins or adhesins for the intestinal mucosal surface. Also, the adhesion characteristics of EAggEC strains may be too complex to be assessed by simple hemagglutination tests.

Purification and characterization of N-glycolyneuraminic-acid-specific lectin from Scylla serrata

A sialic-acid-binding lectin with specificity for N-glycolylneuraminic acid (NeuGc) was purified from the hemolymph of the marine crab Scylla serrata by affinity chromatography using thyroglobulin-coupled agarose. The binding specificity of Scylla lectin distinguishes it from other known sialic-acid-specific lectins found in Limulus polyphemus and Limax flavus, which show a broader range of specificity for sialic acids. The molecular mass of the purified lectin is about 55 kDa. Under reducing conditions (SDS/PAGE), it resolved into two subunits of 30 kDa and 25 kDa. NeuGc inhibited hemagglutination activity of the purified lectin at a concentration as low as 0.6 mM, whereas N-acetylneuraminic acid (NeuAc) even at a concentration of 100 mM, failed to inhibit hemagglutination. This finding was supported by potent inhibition of hemagglutination by bovine and porcine thyroglobulins, which contain a NeuGc alpha 2-6Gal as terminal component of oligosaccharide residues. Neither glycoproteins (glycophorin NN; porcine submaxillary mucin), which contain NeuAc alpha 2-3Gal/GalNAc and NeuAc alpha 2-6GalNAc, nor human acid glycoprotein, which contains NeuAc alpha 2-3/alpha 2-6 Gal, or colominic acid, a sialopolymer with NeuAc alpha 2-8NeuAc, inhibited the lectin activity. The specificity of the lectin for NeuGc appears to account for the fact that it agglutinates rabbit and mice erythrocytes, but not human A, O, AB, rat or chicken erythrocytes, which contain NeuAc. The inability of the lectin to agglutinate erythrocytes (horse) that prominently express NeuGc could be due to O-acetylation of NeuGc. In support of this, bovine submaxillary mucin, which contains O-acetylated NeuGc inhibited the hemagglutination of the lectin better after removal of O-acetyl groups by base treatment. The unique specificity of Scylla lectin is of diagnostic potential for human cancer tissues expressing NeuGc, since NeuGc is not found in normal human tissues.

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.

Characterization of the major and minor mucus glycoproteins from bovine submandibular gland

Two mucins were isolated from bovine submandibular glands and termed major and minor on a quantitative basis. The major mucin representing over 80% of the total glycoprotein fraction contained 37% of its dry weight as protein in contrast to 62% for the minor mucin. Differences in the amino acid composition reflected the higher proportion of typically non-glycosylated peptide in the minor mucin. The molar ratio of N-acetylgalactosamine to serine plus threonine was 0.82 in major and 0.65 in minor mucins, indicating a lower degree of substitution of potential glycosylation sites in the minor mucin. Differences in the carbohydrate composition were found largely related to the sialic acids, with higher relative amounts of N-glycoloylneuraminic acid in the minor mucin. In addition, the proportion of di-O-acetylated sialic acids was higher in the major mucin. The rate of sialidase action on the two mucins could be correlated with the content of N-glycoloylneuraminic acid in each glycoprotein. There was no difference in the type of oligosaccharide found in each mucin and the differences in relative proportions reflected the monosaccharide composition for the two mucins. Gel filtration on Sepharose CL 2B showed a lower molecular weight distribution for the minor in contrast to the major mucin which was partially excluded. Density gradient centrifugation reflected this variation. SDS-PAGE demonstrated a regular banding pattern for the major mucin with a lowest subunit size of 1.8 x 10(5) Da and aggregates in excess of 10(6) Da, while the minor mucin ranged from 3.0 x 10(5) to 10(6) Da. The chemical composition of the isolated mucins was compared with previous histochemical analysis of mucin distribution in bovine submandibular glands and indicates a possible cellular location for each mucin.

Analytical detection of 9(4)-O-acetylated sialoglycoproteins and gangliosides using influenza C virus

The unique glycoprotein of influenza C virus, designated hemagglutinin (HEF), exhibits three functions: hemagglutination, esterase activity, and fusion factor. As the virus uses 9-O-acetylated sialic acid as a high-affinity receptor determinant for attachment to cells, its binding activity was used to reveal O-acetylated sialic acid residues after polyacrylamide gel electrophoresis and transfer onto nitrocellulose sheets of proteins and thin-layer chromatography of lipids. The specificity of the binding for O-acetylated sialoglycoconjugates was investigated. Our results showed that influenza C virus could detect the different forms of the two murine glycophorins which are known to be O-acetylated sialoglycoconjugates. The virus also bound to O-acetylated gangliosides isolated from embryonic chicken brain such as purified O-acetylated NeuAc alpha (2-8)NeuAc alpha (2-8)NeuAc alpha (2-3)Gal beta (1-4)Glc beta (1-1)ceramide (GT3). The esterase activity of the HEF protein of influenza C virus was used to unmask the sialic acid. After its deacetylation by the virus enzyme, the O-acetylated GT3 was recognized by a monoclonal antibody which binds only to the nonacetylated derivative. The results presented here show that influenza C virus is a discriminating analytical probe for identifying O-acetylated sialoglycoconjugates directly after Western blotting of proteins and thin-layer chromatography of lipids, thus providing a new analytical tool.

Species specificity in mouse glycophorin

89, 65, 46 and 29 Kd mouse glycophorin proteins identified during polyacrylamide electrophoresis of mouse erythrocytes have been further characterized. These proteins (1) stain positive with Periodic Acid Schiff reagent after sodium hydroxide treatment; (2) labeled using [125I] in intact cells; (3) co-isolated along with integral membrane proteins in the pellet fraction of sodium hydroxide treated ghosts; and (4) demonstrated a molecular weight downshift after neuraminidase treatment during electrophoresis. We have called them mouse Sialoglycoproteins 1, 2, 3 and 4. Immuno-blot analysis revealed distinct species specificity between human and mouse erythrocyte ghosts, and some cross-reactivity between rat and mouse erythrocyte ghosts.

IgM natural autoantibodies against bromelain-treated mouse red blood cells recognise carbonic anhydrase

Carbonic anhydrase (CA) from mouse erythrocyte membranes is recognised as an autoantigen in Western blotting experiments with FUB 1, a murine IgM monoclonal antibody that binds both phosphatidylcholine and bromelain-treated mouse red blood cells (BrMRBC). Serum from mice stimulated with lipopolysaccharide (LPS-serum) also recognises CA. From SDS-PAGE, and blotting experiments with whole mouse erythrocytes, we found two closely spaced glycoprotein bands in the 30 kD region that reacted with both FUB 1 and LPS-serum. One of the molecular weight markers, bovine carbonic anhydrase which is of a molecular weight of about 30 kD, electrophoresed in the same 30 kD region also reacted with these antibodies. Carbonic anhydrases from a range of mammalian species were found to be crossreactive with FUB 1 and LPS-serum by Western blotting, whereas human glycophorin A and human asialoglycophorin were not recognised by the antibodies. FUB 1 specifically recognises both native and denatured bovine carbonic anhydrase in ELISA assays. The serological identity of the determinants of CA and BrMRBC was confirmed by specific absorption of both FUB 1 and LPS-serum with BrMRBC and normal mouse erythrocytes. We propose that a native autoantigenic epitope on erythrocytes may be revealed by the proteolytic action of bromelain and that this determinant is associated, at least in part, with carbonic anhydrase.

Structural analysis of the carbohydrate chains of a mouse monoclonal IgM antibody

A mouse monoclonal IgM antibody, directed against human blood group B determinant, was isolated from hybridoma culture growth medium. Chemical analysis indicated presence of N- and O-linked oligosaccharides. The N- and O-linked carbohydrate chains were liberated using two different conditions of reductive alkaline degradation. Structural analysis was carried out on the isolated chains using chemical analysis, 500-MHz 1H-NMR spectroscopy and fast-atom-bombardment mass spectrometry. The following composite structures of the N-linked chains were found: (formula; see text) where R = OH for biantennary structures and R = Neu5Ac alpha 2-3Gal beta 1-4 GlcNAc beta 1- or Neu5Ac alpha 2-3Gal beta 1-3[Neu5Ac alpha 2-6]GlcNAc beta 1- for triantennary structures. The O-linked oligosaccharides, found in the light chains, were shown to have the structure Neu5Ac alpha 2-3Gal beta 1-3GalNAc. The native IgM antibody could be separated on a concanavalin-A-Sepharose column into two subfractions, differing in the presence of a high-mannose-type oligosaccharide.

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).

Alkali-labile oligosaccharide units of a sialoglycoprotein from rabbit erythrocyte membranes

Two glycoproteins (apparent molecular weights 120,000 and 70,000) were extracted from rabbit erythrocyte membranes, and only one (Mr 120,000), which is a sialoglycoprotein, contained O-glycosidically linked sugar chains. Alkali-labile oligosaccharide units of the sialoglycoprotein were released as reduced oligosaccharides by NaOH-NaB3H4 treatment, and then purified by gel filtration on a Bio-Gel P-4 column followed by ion-exchange chromatography. From the results of methylation analysis, mass spectrometry and chromium trioxide oxidation, the main oligosaccharide unit was determined to be a linear trisaccharide (85% by weight), NeuNGc alpha(2----3)Gal beta(1----3)GalNAcol. In addition, small amounts of a tetrasaccharide (11% by weight) and a disaccharide (4% by weight) were found, which were determined to have the following structures, NeuNGc alpha(2----3)Gal beta(1----3)[NeuNGc alpha(2----6)] GalNAcol and Gal-GalNAcol, respectively.

Differential interaction of reovirus type 3 with sialylated receptor components on animal cells

In this report we study the interaction of reovirus type 3 Dearing (RV3) with vertebrate erythrocytes whose membrane glycoconjugates differ in the degree and position of O-acetylation of their sialic acid (NeuAc) residues. Binding to erythrocytes required the presence of NeuAc on cellular glycoconjugates, since pretreatment with sialidase (neuraminidase) abolished hemagglutination by RV3. Furthermore, we found that RV3 binds efficiently to and hemagglutinates all erythrocyte preparations possessing exclusively NeuAc, or a mixture of NeuAc and 4-O-acetyl-NeuAc (4-O-Ac-NeuAc), but poorly to erythrocytes bearing a mixture of 9-O-Ac-NeuAc and NeuAc, suggesting that RV3 binds preferentially to NeuAc-containing glycoconjugates. To gain further evidence for this hypothesis we treated chicken erythrocytes with influenza C virus neuraminate, 9-O-acetylesterase, to convert their 9-O-Ac-NeuAc residues to NeuAc. When hemagglutination assays were carried out on these cells, we observed a 16-fold increase in the hemagglutination titer for RV3 compared to untreated cells. When we treated bovine submaxillary mucin (BSM) with influenza C virus, we observed a dramatic increase in its potency as an inhibitor of RV3 hemagglutination. Concomitant with this, the 9-O-Ac-NeuAc residues on BSM were converted to NeuAc. Taken together and in conjunction with a previous report (A. F. Pacitti and J. R. Gentsch, 1987, J. Virol. 61 1407-1415), these results suggest that the virion attachment protein exhibits a strong preference for NeuAc over 9-O-Ac-NeuAc as a receptor component on erythrocytes.

An unique specificity of a sialic acid binding lectin AchatininH, from the hemolymph of Achatina fulica snail

A sialic acid-binding lectin, AchatininH, from the hemolymph of Achatina fulica snail is found to be highly specific for 9-0-acetyl sialic acid. The binding specificity of AchatininH distinguishes it from other known sialic-acid specific lectins which usually show a broader range of specificity for sialic acid. It is even better than crab lectin which shows specificity for both 4- and 9-0-acetylated derivatives of sialic acid. This limited specificity of AchatininH appear to account for the fact that it agglutinates only rabbit, rat and guinea pig erythrocytes which contain 9-0-acetylated sialic acid but not horse (mainly contain 4-0-acetylated sialic acid), human, monkey, sheep, goat and chicken erythrocytes which contain either N-acetyl or N-glycolyl neuraminic acid but no 0-acetylated derivatives. This finding was further supported by the potent inhibition of hemagglutination by free 9-0-acetylated neuraminic acid and by several glyco shingolipids of human origin having 0-acetylated sialic acid.

Identification of rat erythrocyte antigens with a new non-radioactive immunoprecipitation technique

In order to examine how rat erythrocytes stimulate erythrocyte autoantibody production at the molecular level, we have identified rat erythrocyte antigens by immunoprecipitation and western blotting using monoclonal antibodies and antisera. A novel non-radioactive immunoprecipitation technique was used, which employed biotin as a label and a luminescent detection system. The new method was validated by comparison with conventional immunoprecipitation using 125I. Glycophorins of relative molecular mass (Mr) 81,000 and 38,000 were found to be the major antigenic components of rat erythrocytes, while band 3 (the most abundant erythrocyte membrane protein) was not recognized by rat-specific antibodies. The same surface antigens were recognized by sera from mice producing erythrocyte autoantibodies and by sera from mice in which autoantibody production was suppressed. Nine other minor rat-specific antigens were identified by blotting, ranging in Mr from 23,000 to 147,000. Analysis of the integral membrane proteins of rat and mouse erythrocytes by sodium dodecyl sulphate (SDS) electrophoresis followed by silver or periodic acid-Schiff (PAS) stains revealed differences between the glycophorins, but not between rat and mouse band 3. Thus, the major antigenic differences correspond to discernible biochemical differences between rat and mouse erythrocyte sialoglycoproteins.

High and low molecular weight tracers for the electron microscopical detection of sialoglycoconjugates

Hydrazide-derivative tracers of different molecular weights have been synthesized for use in the electron microscopical detection of sodium periodate-oxidized sialyl residues of glycoconjugates in various tissues and cells. Haemundecapeptide hydrazide, horseradish peroxidase hydrazide, and Limulus polyphemus haemocyanin hydrazide were obtained by coupling adipic acid dihydrazide to the tracers with the aid of water-soluble carbodiimide. The enzymatic tracers thus prepared retained their peroxidatic activity. On conversion to the hydrazide derivative, the haemocyanin molecule dissociated into its hexameric subunits. In order to test by transmission electron microscopy the ability of the conjugates to bind to the sialoglycoconjugates of endothelial cell surfaces, each tracer was perfused in situ into rat pancreatic vasculature previously oxidized with 1 mM sodium periodate. The three tracers characteristically labelled the various microdomains of the luminal cell coat of the capillary endothelial cell. The electron opacity of the haemocyanin subunits allowed their easy detection when bound to the cell surface or to components of the extracellular matrix. The bound markers were not displaced by a high ionic strength buffer, and did not label desialylated cell surfaces. These results indicate that the three hydrazide-derivative tracers may be useful tools for the electron microscopical detection of cellular and extracellular sialoglycoconjugates.

Luminescent visualization of antigens on blots

Proteins separated by SDS gel electrophoresis and transferred to a nitrocellulose sheet can be visualised by 'probing' with peroxidase-linked reagents which are detected by luminescence. A modified luminescent substrate is described containing 4-methylumbelliferone which enhances light emission four-fold. Using the modified substrate, luminescent detection was found to be more sensitive than chromogenic detection of peroxidase using 4-chloro-1-napthol. The new technique was used in conjunction with the immunoblot method to demonstrate antigenic differences between rat and mouse erythrocytes.

Sialic acid analysis and tritium-labelling of sialoglycoproteins of mouse erythrocytes infected with Plasmodium berghei

Schizont-infected red blood cells (SI-RBC) from Plasmodium berghei-infected mice contain between 2 and 10 times as much sialic acid as uninfected RBC from the same blood (99-550 micrograms/10(10) RBC versus 33-65 micrograms/10(10) RBC). Total RBC samples from infected animals containing up to 63% ring- and trophozoite-infected cells had identical sialic acid contents to purified RBC samples (of less than 3% parasitaemia) from the same blood (52-64 micrograms/10(10) RBC). We conclude that RBC containing immature parasites have the same sialic acid content as uninfected RBC from infected blood and that total cellular sialic acid increases during maturation to the schizont stage. Uninfected RBC from infected blood had 25-50% as much sialic acid as normal mouse RBC (33-65 micrograms/10(10) RBC versus 126 micrograms/10(10) RBC). There were no qualitative changes in RBC sialic acids, all RBC samples having 60-70% N-acetylneuraminic acid, 30-40% N-acetyl-9-O-acetylneuraminic acid and 5-10% N-glycolylneuraminic acid. The quantitative changes we observed during infection must reflect changes in murine sialoglycoconjugates, as we have shown elsewhere that Plasmodia do not synthesize or contain sialic acids. Since the sialic acid composition of mouse serum glycoconjugates is quite different to that of the RBC fractions studied here, the quantitative data suggest that part of the sialic acids of the uninfected RBC has been transferred to SI-RBC. With higher molar ratios of periodate to substrate than generally used, we were able to radio-isotopically label normal murine sialoglycoproteins on SI-RBC and purified uninfected RBC from infected blood by the periodate/NaB3H4 method. Several new proteins were then tritiated with SI-RBC but these proteins may be intracellular and could even lack sialic acid.

Induction of glycophorin gene expression in cultured murine erythroleukemia cells

In order to identify the mRNA for mouse glycophorin, mRNA was isolated from immature erythroid cells obtained from the spleens of anemic mice, translated in vitro in mRNA-dependent rabbit reticulocyte lysate, and then immunoprecipitated with a specific antiserum. Glycophorin mRNA was shown to be present only in erythroid cells. In immunofluorescent and in vitro translation studies, it was shown that glycophorin mRNA is absent in uninduced murine erythroleukemia (MEL) cells, but is induced in dimethylsulfoxide-treated differentiating cells.

The release and purification of sialic acids from glycoconjugates: methods to minimize the loss and migration of O-acetyl groups

The sialic acids can have O-acetyl esters at the 4, 7, 8, and 9 positions. Most methods for the detailed study of such molecules require their release from glycosidic linkage, followed by extensive purification. The currently used methods for release and purification of sialic acids allow a reasonable qualitative analysis of the diversity of sialic acids from a given biological source. However, for several reasons, quantitative assessment of the degree and type of O-acetylation is not possible with these methods. Previously known problems include the incomplete and nonrandom release of the different sialic acids by both enzymatic and chemical means, and extensive destruction of the O-acetyl esters (de-O-acetylation) during the release and purification. An additional problem, that migration of O-acetyl groups from the 7 or 8 positions to the 9 position can occur under the conditions of release and purification, particularly when the pH is above 6 or below 3.0, is demonstrated here. It is shown that the O-acetyl esters on free sialic acids are relatively more stable under acid conditions but more labile under basic conditions than similar esters on bound sialic acids. An analysis of the various steps of the conventional purification procedure showed that exposure to the basic anion-exchange resin is the critical step that results in de-O-acetylation and O-acetyl migration. Based upon these and other findings some new methods have been devised, and several modifications of the existing methods have been suggested, that allow the quantitative release and purification of sialic acids with minimal loss of O-acetyl groups. The migration of O-acetyl groups is also decreased by these modifications, but cannot be completely controlled.

Changes in the glycoprotein composition of plasma membrane during the differentiation of friend erythroleukemia cells

Friend erythroleukemia cells display transient and permanent changes in the composition of their plasma membrane-bound glycoproteins during dimethyl sulfoxide-induced differentiation. The transient changes, as revealed by metabolic labeling with [14C]glucosamine, are most conspicuous around the time during which most cells become committed to terminal differentiation. Permanent changes are revealed by reductive tritiation after oxidation with NaIO4 or galactose oxidase. In differentiated cells one glycoprotein fraction (Mr 150 000) could not be labeled by any of these methods, although it does contain neuraminic acid. We found no evidence in support of the hypothesis that the anomalous behavior of this fraction is caused by an increased degree of O-acetylated neuraminic acid in the plasma membrane of differentiated cells.

Partial purification of amino acid transport systems in Ehrlich ascites tumor cell plasma membranes

Ehrlich ascites tumor cell plasma membranes were subjected to sequential selective protein extraction to identify protein components associated with amino acid transport. These membranes were extracted with Triton X-100 followed by 2,3-dimethylmaleic anhydride. Approximately 80% of the membrane proteins were extracted by these procedures while the original lipids were largely retained (approximately 70%). The quantity of carbohydrate per milligram protein in the residue increased on extraction, consistent with an enrichment of glycoprotein in the residue. The residual vesicles display the characteristic properties of Na+-coupled amino acid transport. These properties include Na+-stimulated uptake and Na+-gradient-stimulated uptake leading to an accumulation of the solute against its chemical gradient as well as inhibition of uptake by a competitive amino acid, L-methionine. The extracted vesicles exhibit a peak level of alpha-aminoisobutyrate uptake six times greater than that expected from equilibration of alpha-aminoisobutyrate. This accumulation is greater than that obtained with native vesicles, albeit slower. The accelerated exchange diffusion of L-leucine is not measurable in the residual vesicles after dimethylmaleic acid anhydride treatment, although it can be measured after Triton extraction. These results are consistent with the conclusion that the amino acid transport systems "A" (Na+-coupled) and "L" (Na+-independent) in Ehrlich cells, though having overlapping specificities for amino acids, and distinct physical entities.

Identification of a glycophorin-like molecule at the cell surface of rat thymocytes

There are three predominant glycoproteins in the rat thymocyte plasma membrane. Two of these have carbohydrate compositions that are characteristic of structures N-glycosidically linked to protein. The other glycoprotein is very different, having about 20 O-glycosidically linked carbohydrate units per 100 amino acids. It has similarities to the major sialoglycoprotein of human erythrocytes.