A new cold agglutinin from Achatina fulica snails

Physiology and immunity of the invasive giant African snail, Achatina (Lissachatina) fulica, intermediate host of Angiostrongylus cantonensis

As one of the most successful invasive land snail species, Achatina (Lissachatina) fulica Bowdich, 1822 has achieved wide global distribution, particularly in (sub)tropical regions, with further dispersal likely due to climate change. This species of giant African snails (up to 17 cm shell length) is a pest that has extensive negative impact on agriculture and can serve as vector for several parasites, including Angiostrongylus cantonensis, a nematode parasite that causes (human) eosinophilic meningitis, an emergent disease. Investigation showed that A. cantonensis infection negatively impacts the metabolism of A. fulica by depleting polysaccharide stores of the intermediate host, compromising the energy balance of the snail. A review of the literature indicates that A. fulica possesses potent innate type immune defenses to counter infection, including phagocytic hemocytes capable of deploying reactive oxygen species and lectins for non-self recognition, a serine protease-dependent coagulation response (not observed in other taxa of gastropods), as well as antimicrobial proteins including achacin, an antimicrobial protein. A recent chromosome level genome assembly will facilitate progressively detailed characterization of these immune features of A. fulica. We strongly encourage further immunological studies of A. fulica, ranging from organismal level to molecular biology to gain better understanding of the A. fulica internal defense response to nematode pathogens like A. cantonensis and the contribution of immune function to the invasiveness of (snail) species. Characterization of immunity of A. fulica, representing the understudied Stylommatophora (panpulmonate landsnails) will also broaden the comparative immunology of Gastropoda.

Purification, characterization of O-acetylated sialoglycoconjugates-specific IgM, and development of an enzyme-linked immunosorbent assay for diagnosis and follow-up of indian visceral leishmaniasis patients

The surface expression of 9-O-acetylated sialic acid (9-OAcSA) is elevated on hematopoietic cells and erythrocytes of visceral leishmaniasis (VL) patients. In this study, we show that VL patients contain elevated levels of IgM antibodies directed against 9-O-acetylated sialoglycoconjugates (9-OAcSG). These antibodies were affinity purified with bovine submaxillary protein as the affinity matrix containing the terminal epitope, 9-OAcSAalpha2-6GalNAc. They also bound to 9-OAcSGs on hematopoietic cells of patients with VL and to epitopes in the cytosol of Leishmania donovani promastigotes. A novel enzyme-linked immunosorbent assay was employed that showed 4-fold higher anti-OAcSG titers in VL patients (n=38), mean +/- S.E.M. being 0.83 +/- 0.09 vs. 0.21 +/- 0.04 detected in normal donors (n=20) and patients with cross-reactive diseases such as malaria (n=4) or tuberculosis (n=4). Assay specificity and sensitivity was 100% and 92%, respectively, whereas positive and negative predictive values were 100% and 90%, respectively. Significantly, anti-OAcSG titers declined 30 days after completion of anti-leishmanial treatment, indicating that monitoring of anti-9-OAcSGs may be a valuable alternative toward increasing the efficiency of diagnosis and follow-up of VL.

Role of linkage specific 9-O-acetylated sialoglycoconjugates in activation of the alternate complement pathway in mammalian erythrocytes

Substitution of the -OH group at C-9 of sialic acid by an O-acetyl ester has been suggested to modify various biological phenomena that are regulated by sialic acids. Amongst them, enhancement of erythrocyte lysis by 9-O-acetylated sialic acid determinants through modulation of the alternate pathway of complement has been extensively studied on murine erythrocytes [1]. A variable expression of linkage specific 9-O-acetylated sialoglycoconjugates as defined by the lectinogenic epitope of Achatinin-H namely 9-O-acetylated sialic acid alpha2-->6Gal NAc was identified on rabbit, guinea pig, hamster, rat, mouse and human erythrocytes. This differential expression of linkage specific 9-O-acetylated sialoglycoconjugates strongly correlated with the susceptibility of mammalian erythrocytes to lysis by the alternate pathway of complement. Additionally, low levels of antibodies directed against O-acetylated sialic acids in these mammalian species suggested that these constitutively present determinants have low immunogenicity. Taken together, our results indicate that complement mediated hemolysis depends not simply upon the extent of surface 9-O-acetylated sialic acids present but more importantly upon the specific linkage.

Identification and purification of cytolytic antibodies directed against O-acetylated sialic acid in childhood acute lymphoblastic leukemia

Sialic acids typically present as terminal sugars of oligo-saccharides are reported to be modified by O-acetylation at the C-9 position on lymphoblasts of childhood acute lymphoblastic leukemia (ALL) patients (Sinha et al., 1999a, Leukaemia, 13, 119-125). We now report high titers of IgG antibodies directed against O-acetylated derivatives of sialic acids (O-AcSA) in serum of ALL patients. These antibodies were purified using bovine submaxillary mucin (BSM) and the IgG distribution was confined to IgG(1)and IgG(2)subclasses; their binding was totally abolished with de-O-acetylation confirming their specificity towards O-AcSA determinants. Flow cytometry demonstrated binding of these antibody fractions to peripheral blood mononuclear cells (PBMC) of both T- and B-ALL patients having increased cell surface 9-O-AcSA determinants. Western blotting of membranes derived from PBMC of ALL patients confirmed binding of the antibody to O-acetylated sialoglycoconjugates corresponding to 144, 135, 120, 90, and 36 kDa whereas binding to PBMC from normal individuals corresponded to 144 and 36 kDa. Specificity of the antibody fraction towards 9-O-AcSA was substantiated by hemagglutination and hemagglutination-inhibition assays. The antibody purified from ALL serum selectively mediates complement dependent cytolysis of lymphoblasts expressing O-AcSAs and thereby possibly confers passive protection. The enhanced anti O-AcSA antibody levels allowed for development of a serodiagnostic assay (BSM-ELISA) specific for ALL. Minimal crossreactivity was observed with other hematological disorders like acute myeloid leukemia (n = 16), chronic myeloid leukemia (n = 6), chronic lymphocytic leukemia (n = 7) and non-Hodgkin's lymphoma (n = 3) as well as normal healthy individuals (n = 28). The BSM-ELISA therefore provides a simple, noninvasive alternative diagnostic approach for ALL and merits clinical consideration.

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.

Polylactosamine sugar chains expressed by epithelia of Henle's loop and collecting duct in rat and human kidney are selectively recognized by human cold agglutinins anti-I/i

Normal rat and human kidney was mapped immunohistochemically with human monoclonal cold agglutinins against the biochemically related erythrocyte glycoconjugate antigens I and i, which represent branched and linear polylactosamines, respectively. The antibodies worked well with both cryostat and paraffin-embedded material. Anti-i gave specific staining of collecting duct cells (mostly principal cells) as evidenced by double labelling with antibodies to band 3 and a 23 kD protein of intercalated cells. In contrast, anti-I turned out to be the first exclusive marker for the ascending and descending thin limb of Henle's loop. In addition, in rat kidney, the binding of anti-I/i was preserved in primary cultures both of principal cells of the papillary collecting duct and cells of the thin limb of Henle's loop. Our results suggest that both antibodies might be interesting tools for in vitro studies of renal cell physiology and the investigation of kidney development.

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.

Purification of an agglutinin from the haemolymph of the snail Bulinus nasutus and demonstration of related proteins in other Bulinus spp

The snail Bulinus nasutus 1214 possesses a potent haemagglutinin (end-point titre with human erythrocytes, 2(-18)) in its cell-free haemolymph which also binds to the miracidia (but not other larvae) of the incompatible parasite Schistosoma margrebowiei. We have purified a protein possessing this haemagglutinating property from the plasma of this snail. The native Mr of this protein was estimated by SDS polyacrylamide gel electrophoresis to be 210 kDa; under denaturing conditions in a 7.5% PAGE gel it ran as a major band of 135 kDa. Proteins of similar Mr were also found in the haemolymph of 16 other Bulinus spp. (the major intermediate hosts of human and veterinary schistosomiasis in Africa) although the plasma of none of these agglutinated human erythrocytes. Nonetheless, Cleveland mapping of the Mr 135 kDa bands from these different Bulinus spp. revealed 4 identical major peptide fragments (30, 28, 19 and 16 kDa) in each, thus demonstrating a similarity in the primary structure of these plasma proteins. Antisera from Balb/C mice immunized with the 135 kDa polypeptide from Bulinus truncatus 1521 cross-reacted in Western blots with the 135 kDa band of other members of the same truncatus/tropicus species complex but not with species from the africanus or forskalii species groups.

Isolation and characterization of a lectin from the cephalochordate Branchiostoma lanceolatum (Pallas)

1. A lectin was isolated from an extract of Branchiostoma lanceolatum by affinity chromatography using an asialo-A-peptone-cellulose column. 2 The lectin is a glycoprotein with a carbohydrate content of 2.7%. The mol. wt is 392,000 +/- 28,000. Two subunits of identical size (183,000 +/- 3000) are linked by non-covalent bonds. 3. The lectin agglutinates a variety of erythrocytes including human A, B, O red blood cells as well as human lymphocytes. 4. Hemagglutination activity is inhibited best by N,N',N"-triacetylchitotriose, followed by N,N'-diacetylchitobiose, which is half as inhibitory. 5. Lectin activity is constant between pH 5 and 10. Divalent cations are not required for binding reactions. Activity is totally destroyed by heating to 60 degrees C for 30 min. 6. The lectin is precipitated from the extract by 30-40% ammonium sulfate saturation.

The polyclonal activation of lymphocytes and T cell mitogenicity by a unique sialic-acid-binding lectin from the hemolymph of Achatina fulica snail

A unique sialic-acid-binding lectin, AchatininH, isolated from the hemolymph of Achatina fulica snail was found to be strongly mitogenic, as monitored by [3H]thymidine incorporation assay, to rat and human lymphocytes. However, the degree of mitogenic response varied with the type of cell population. As indicated, this lectin induced proliferation of purified T lymphocytes and rat thymocytes, whereas it was less mitogenic towards peripheral lymphocytes of pregnant rats and was not mitogenic towards B lymphocytes. Furthermore, the mitogenic response was inhibited by the sialic-acid-containing disaccharide, a strong inhibitor of this lectin. This suggests that lymphocyte cell surface molecules containing sialic acid residues are important for this interaction and may have a structure similar to that of AchatininH receptors. Although this lectin showed strong mitogenicity towards lymphocytes, it showed very weak leucoagglutination. Surprisingly, PHA-induced blastogenesis was inhibited by the same dose of AchatininH as caused mitogenic activity in resting lymphocyte culture. The degree of suppression was higher for the lymphocytes isolated from pregnant rat blood compared to the non-pregnant control. Since the 51Cr-uptake assay and the cell viability test results negate the potential cytotoxic activity of this protein, the immunosuppression induced in the presence of PHA by AchatininH may be the additive effect of two mitogens causing an increased cell-density-dependent arrest. AchatininH does not have complement-like activity, but induces potent polyclonal activation of B cells as measured by the reverse hemolytic plaque assay.

Physicochemical studies of binding of 4-methylumbelliferyl beta-D-galactopyranoside to cold agglutinin

The fluorescence of 4-methylumbelliferyl beta-D-galactopyranoside (MeUmbGalp) was quenched in the presence of cold agglutinin, showing that there was binding between MeUmbGalp and cold agglutinin. That binding was saccharide-specific. By using this quenching phenomenon, the association constants (Ka) of the binding of cold agglutinin at different temperatures (10 degrees C and 15 degrees C) to MeUmbGalp and also the number of binding sites were calculated. The Ka values were found to be 2.63 x 10(3) M-1 at 10 degrees C and 1.58 x 10(3) M-1 at 15 degrees C. Though there is a change in Ka values, the number of binding sites was calculated to be six at both temperatures (10 degrees C and 15 degrees C). From the Ka values the thermodynamic parameters (free energy, enthalpy and entropy) of the binding were derived, and analysis of the data indicated that the binding is spontaneous, exothermic and hydrophobic in nature.

Physiochemical studies on achatininH, a novel sialic acid-binding lectin

We have purified a sialic acid-binding lectin, achatininH, in a single step by affinity chromatography, having high affinity for 9-O-acetylneuraminic acid. The physicochemical characterization of the interaction of achatininH with bivalent metal ions and sialic acid derivatives by the use of spectrofluorimetry, spectropolarimetry and precipitin reaction is reported. From fluorescence quenching studies the binding of Ca2+ (Ka = 251 +/- 9 M-1) and of Mn2+ (Ka = 86 +/- 5 M-1) was found to be weak, but their presence is absolutely necessary for sugar binding as well as biological activity. The nature and position of the substituent group play a very important role in the binding affinity. AchatininH shows a high affinity for 9-O-acetylneuraminic acid (Ka = 1.20 x 10(3) +/- 0.07 x 10(3) M-1) compared with that for the 4-O-acetyl derivative. In oligomers the binding strength increases in the order monosaccharide less than disaccharide less than trisaccharide. The binding affinity of achatininH for the disaccharide was found to reach a peak around pH 8. From c.d. spectral studies achatininH was found to have a high beta-sheet content (46%) and a low alpha-helix content (24%). From precipitin analysis at least one sugar-binding site on each of the 16 monomer subunits of the protein is indicated.

Purification and characterization of an agglutinin from mucus of the snail Achatina fulica

The mucus of the snail Achatina fulica shows the presence of an agglutinin that nonspecifically agglutinates human erythrocytes. The agglutinin has been purified by affinity chromatography using Sepharose 4B-hog gastric mucin as the affinity matrix. Homogeneity was checked by polyacrylamide gel electrophoresis, immunodiffusion, immunoelectrophoresis, and gel filtration. The agglutinin is a glycoprotein of native molecular weight 70,000. The isoelectric point of the protein was found to be 8.0. The predominant amino acids are aspartic acid and glutamic acid (or amides) and serine, which account for 32% of the total amino acid residues. The agglutinin has 10% carbohydrate (wt/wt) and the most abundant sugar is N-acetylglucosamine. The cd spectra of the agglutinin show the presence of random coil conformation. The inhibition of hemagglutination data indicates that the agglutinin is specific for beta glycosides of D-Gal and D-GalNAc.

Chemical-modification studies of a unique sialic acid-binding lectin from the snail Achatina fulica. Involvement of tryptophan and histidine residues in biological activity

A unique sialic acid-binding lectin, achatininH (ATNH) was purified in single step from the haemolymph of the snail Achatina fulica by affinity chromatography on sheep submaxillary-gland mucin coupled to Sepharose 4B. The homogeneity was checked by alkaline gel electrophoresis, immunodiffusion and immunoelectrophoresis. Amino acid analysis showed that the lectin has a fairly high content of acidic amino acid residues (22% of the total). About 1.3% of the residues are half-cystine. The glycoprotein contains 21% carbohydrate. The unusually high content of xylose (6%) and fucose (2.7%) in this snail lectin is quite interesting. The protein was subjected to various chemical modifications in order to detect the amino acid residues and carbohydrate residues present in its binding sites. Modification of tyrosine and arginine residues did not affect the binding activity of ATNH; however, modification of tryptophan and histidine residues led to a complete loss of its biological activity. A marked decrease in the fluorescence emission was found as the tryptophan residues of ATNH were modified. The c.d. data showed the presence of an identical type of conformation in the native and modified agglutinin. The modification of lysine and carboxy residues partially diminished the biological activity. The activity was completely lost after a beta-elimination reaction, indicating that the sugars are O-glycosidically linked to the glycoprotein's protein moiety. This result confirms that the carbohydrate moiety also plays an important role in the agglutination property of this lectin.

Wistaria sinensis agglutinin: purification, carbohydrate specificity, and characterisation of the combining site

A 2-acetamido-2-deoxy-D-galactose-binding agglutinin from Wistaria sinensis seeds, purified by affinity chromatography on a 2-acetamido-2-deoxy-D-galactose-starch conjugate, was homogeneous as judged by poly(acrylamide) disc gel electrophoresis. It had a mol. wt. of 66,000 (gel filtration on Sephadex G-150); on electrophoresis on SDS-poly(acrylamide) gel in the presence of 2-mercaptoethanol, it dissociated into sub-units of mol. wt. 34,000, suggesting the agglutinin to be a dimer; and it was a glycoprotein containing 4.8% of carbohydrate. It agglutinated several vertebrate erythrocytes, including human regardless of the blood group. In hapten-inhibition assays, 2-acetamido-2-deoxy-D-galactose and its glycosides were found to be better inhibitors than D-galactose and its glycosides, but N-acetyl-lactosamine was the most potent inhibitor. The binding involved HO-3,4 of the haptens and HO-2 partially.

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.

Studies on chemical modification of cold agglutinin from the snail Achatina fulica

The cold agglutinin isolated from the albumin gland of the snail Achatina fulica was modified with various chemical reagents in order to detect the amino acids and/or carbohydrate residues present in its carbohydrate-binding sites. Treatment with reagents considered specific for modification of lysine, arginine and tryptophan residues of the cold agglutinin did not affect the carbohydrate-binding activity of the agglutinin. Modification of tyrosine residues showed some change. However, modification with carbodiimide followed by alpha-aminobutyric acid methyl ester causes almost complete loss of its binding activity, indicating the involvement of aspartic acid and glutamic acid in its carbohydrate-binding activity. The carbohydrate residues of the cold agglutinin were removed by beta-elimination reaction, indicating that the sugars are O-glycosidically linked to protein part of the molecule. Removal of galactose residues from the cold agglutinin by the action of beta-galactosidase indicated that the galactose molecules are beta-linked. These carbohydrate-modified glycoproteins showed a marked change in agglutination property, i.e. they agglutinated rabbit erythrocytes at both 10 degrees C and 25 degrees C, indicating that the galactose residues of the glycoprotein play an important role in the cold-agglutination property of the glycoprotein. The c.d. data showed the presence of an almost identical type of random-coil conformation in the native cold agglutinin at 10 degrees C and in the carbohydrate-modified glycoprotein at 10 degrees C and 25 degrees C. This particular random-coil conformation is essential for carbohydrate-binding property of the agglutinin.

Further characterization of the cold agglutinin from the snail Achatina fulica

The cold agglutinin from the albumin gland of the snail Achatina fulica was purified to homogeneity by using sheep gastric mucin-Sepharose 4B as affinity column followed by gel filtration on Bio-Gel P-300. The homogeneity was checked by alkaline gel electrophoresis, immunodiffusion and immunoelectrophoresis. The purified cold agglutinin is a glycoprotein of native M2 220,000 consisting of three non-covalently bound subunits of Mr 84,000, 74,000 and 62,000 and having a pI value of 4.5. The predominant amino acids are aspartic acid and glutamic acid (or amides) and serine, which account for 39% of the residues. About 3% of the residues are half-cystine. The lectin is a glycoprotein with about 30.7% carbohydrate, the most abundant sugars being galactose, N-acetylgalactosamine and N-acetylglucosamine. Mannose, xylose and fucose are also present. The inhibition of agglutination of human umbilical-cord erythrocytes by the cold agglutinin is specific for methyl beta-D-galactoside and also for glycolipids present on cord erythrocytes. The c.d. data show only negative ellipticity values in the far-u.v. region for the protein at various concentrations and temperatures and also in the presence of the hapten lactose (at different concentrations), indicating the presence of a random-coil conformation in the agglutinin that varies according to temperature.

A single step purification of a sialic acid binding lectin (AchatininH) from Achatina fulica snail

A sialic acid binding lectin, AchatininH, was purified in single step from the hemolymph of the land snail, Achatina fulica, by the affinity chromatography on sheep submaxillary mucin coupled to Sepharose 4B. The yield of the lectin was found to be 3 mg from 100 ml of hemolymph. The homogeneity of the lectin was established by alkaline gel electrophoresis, immunodiffusion, immunoelectrophoresis and analytical isoelectrophoresis. The molecular weight of the native protein was 242,000, having identical subunits of Mr 15,000. The lectin agglutinated rabbit erythrocytes in the presence of Ca2+. The inhibition study clearly suggests that the binding site of the lectin recognizes sialic acid as the immunodominant sugar. This was further confirmed by the observation that there was a marked decrease of agglutinating activity of the lectin with neuraminidase treated rabbit erythrocytes and asialofetuin was unable to inhibit the activity of AchatininH. Among the inhibitors used the glycoconjugate containing alpha 2----6 linkages of N-acetylneuraminic acid with subterminal galactopyranose or 2-acetamido-2-deoxy-galactopyranose residue was found to be better inhibitor than that containing alpha 2----3 linkages of N-acetyl neuraminic acid. Besides that sialoglycoprotein containing both N and O type of glycosidic linkages plays an important role in binding with the lectin. Fetuin was found to be the best inhibitor.