Further characterization of the cold agglutinin from the snail Achatina fulica

Localization and characterization of acharan sulfate in the body of the giant African snail Achatina fulica

Acharan sulfate is a glycosaminoglycan (GAG), having the structure -->4)-2-acetamido-2-deoxy-alpha-D-glucopyranose(1-->4)-2-sulfo-alpha-L-idopyranosyluronic acid (1-->, isolated from the body of the giant African snail Achatina fulica. This GAG represents 3-5% of the dry weight of this snail's soft body tissues. Frozen sections and polyester wax sections of the snail's body were stained by Alcian blue-periodic acid-Schiff's reagent (PAS) to localize acharan sulfate. Alcian blue staining indicated that GAG was mainly secreted into the outer surface of the body from internal granules. A highly mucous material was collected and treated and the acharan sulfate was recovered by ethanol and cetyl pyridinium chloride precipitation. Crude acharan sulfate was purified by DEAE-Sephacel ion-exchange chromatography. Depolymerization of intact mucus and purified acharan sulfate fractions by heparin lyase II (heparitinase I) from Flavobacterium heparinum produced an unsaturated disaccharide as a major product, establishing the repeating unit of acharan sulfate. These results demonstrate that mucus in the granule and secreted to the outside of the body is composed entirely of acharan sulfate.

A new glycosaminoglycan from the giant African snail Achatina fulica

A new glycosaminoglycan has been isolated from the giant African snail Achatina fulica. This polysaccharide had a molecular weight of 29,000, calculated based on the viscometry, and a uniform repeating disaccharide structure of -->4)-2-acetyl,2-deoxy-alpha-D-glucopyranose (1-->4)-2-sulfo-alpha-L-idopyranosyluronic acid (1-->. This polysaccharide represents a new, previously undescribed glycosaminoglycan. It is related to the heparin and heparan sulfate families of glycosaminoglycans but is distinctly different from all known members of these classes of glycosaminoglycans. The structure of this polysaccharide, with adjacent N-acetylglucosamine and 2-sulfo-iduronic acid residues, also poses interesting questions about how it is made in light of our current understanding of the biosynthesis of heparin and heparan sulfate. This glycosaminoglycan represents 3-5% of the dry weight of this snail's soft body tissues, suggesting important biological roles for the survival of this organism, and may offer new means to control this pest. Snail glycosaminoglycan tightly binds divalent cations, such as copper(II), suggesting a primary role in metal uptake in the snail. Finally, this new polysaccharide might be applied, like the Escherichia coli K5 capsular polysaccharide, to the study of glycosaminoglycan biosynthesis and to the semisynthesis of new glycosaminoglycan analogs having important biological activities.

A novel galactosyl-binding lectin from the plasma of the blood clam, Anadara granosa (L) and a study of its combining site

The marine blood clam species Anadara granosa (L) belong to arcidae, a family with some extraordinary haematological features. The plasma of this species exhibited strong haemagglutinating activities, from which a galactosyl binding lectin, Anadarin P, was purified in a single step affinity chromatography using Sepharose 4B-asialofetuin as an affinity matrix. The purified lectin, eluted with lactose, was found to be homogeneous by alkaline polyacrylamide disc gels, gel-filtration and isoelectric focusing. Native M(r) of the lectin was 130,000 having a PI value of 6.82 and was composed of two subunits of M(r) 17,000 and M(r) 16,000 which were noncovalently bound. The lectin was remarkably thermostable; the agglutinating titre remained unchanged over a wide range of pH (from 5 to 10) but increased with neuraminidase treated rabbit erythrocytes. Anadarin P combining site has been proposed to be small pocket-like structure which recognised only C-3 and C-4 hydroxyl groups of D-galactose. Presence of bulky groups at C-2 and C-6 exert strong steric hindrance as L-arabinose, 2-deoxy-D-galactose and D-xylose are better inhibitors than D-galactose. The lectin fails to differentiate methyl substituted galactosides as both alpha- and beta- methyl galactosides are equally active; but in case of substituted phenyl glycosides, the lectin shows different affinity towards alpha and beta anomers. The avidity of the lectin to bind the aromatic aglycons of galactosides suggests the presence of a hydrophobic region in the combining site. Interactions with some disaccharides indicate the presence of an extended area near the monosaccharide binding site.

Sialic acid binding lectins

The literature contains several reviews on lectins in general, covering mainly those from plants and invertebrates. However, the sialic acid binding lectins have not been reviewed so far. Considering the importance of sialic acids in cell sociology, lectins which specifically recognize terminal sialic acid residues are potentially useful as analytical tools in studying the biological functions of sialoglycoconjugates. These lectins, along with monoclonal antibodies raised against sialoglycoconjugates, have been used in the detection, affinity purification, cytochemical localization and quantitation of such glycoconjugates. In this review the main emphasis has been placed on the occurrence, general purification procedures, macromolecular properties, sugar specificities and applications of these lectins.

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.

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.

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.