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.

Control of glycoprotein synthesis: substrate specificity of rat liver UDP-GlcNAc:Man alpha 3R beta 2-N-acetylglucosaminyltransferase I using synthetic substrate analogues

UDP-GlcNAc: Man alpha 3R beta 2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is the key enzyme in the synthesis of complex and hybrid N-glycans. Rat liver GlcNAc-T I has been purified more than 25,000-fold (M(r) 42,000). The Vmax for the pure enzyme with [Man alpha 6(Man alpha 3)Man alpha 6](Man alpha 3)Man beta 4GlcNAc beta 4GlcNAc beta-Asn as substrate was 4.6 mumol min-1 mg-1. Structural analysis of the enzyme product by proton nuclear magnetic resonance spectroscopy proved that the enzyme adds an N-acetylglucosamine (GlcNAc) residue in beta 1-2 linkage to the Man alpha 3Man beta-terminus of the substrate. Several derivatives of Man alpha 6(Man alpha 3)Man beta-R, a substrate for the enzyme, were synthesized and tested as substrates and inhibitors. An unsubstituted equatorial 4-hydroxyl and an axial 2-hydroxyl on the beta-linked mannose of Man alpha 6(Man alpha 3)Man beta-R are essential for GlcNAc-T I activity. Elimination of the 4-hydroxyl of the alpha 3-linked mannose (Man) of the substrate increases the KM 20-fold. Modifications on the alpha 6-linked mannose or on the core structure affect mainly the KM and to a lesser degree the Vmax, e.g., substitutions of the Man alpha 6 residue at the 2-position by GlcNAc or at the 3- and 6-positions by mannose lower the KM, whereas various other substitutions at the 3-position increase the KM slightly. Man alpha 6(Man alpha 3)4-O-methyl-Man beta 4GlcNAc was found to be a weak inhibitor of GlcNAc-T I.

Study of foetal antigen in haematological malignancy

Forty patients with different varieties of leukaemia and lymphoma were studied before and after therapy. Red cells and lymphocytes from each patient were tested for foetal antigen by lectin-agglutination test. The antigen was detectable on red cells in all untreated cases, the highest titre being found in chronic myeloid leukaemia. The titre showed significant reduction after treatment in all cases. We conclude that foetal antigen on red cells is a useful diagnostic aid in haematological malignancy and is a good indicator of the outcome of therapy.

Molecular cloning and characterization of the mouse UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I gene

The biosynthesis of protein-bound complex N-glycans in mammals requires a series of covalent modifications governed by a large number of specific glycosyltransferases and glycosidases. The addition of oligosaccharide to an asparagine residue on a nascent polypeptide chain begins in the endoplasmic reticulum. Oligosaccharide processing continues in the Golgi apparatus to produce a diversity of glycan structures. UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (EC 2.4.1.101; GlcNAc-TI) is a key enzyme in the process because it is essential for the conversion of high-mannose N-glycans to complex and hybrid N-glycans. We have isolated the mouse gene encoding GlcNAc-TI (Mgat-1) from a genomic DNA library. The mouse sequence is highly conserved with respect to the human and rabbit homologs and exists as a single protein-encoding exon. Mgat-1 was mapped to mouse Chromosome 11, closely linked to the gene encoding interleukin-3 by the analysis of multilocus interspecies backcrosses. RNA analyses of Mgat-1 expression levels revealed significant variation among normal tissues and cells.

Goat sperm membrane: lectin-binding sites of sperm surface and lectin affinity chromatography of the mature sperm membrane antigens

The cell surface glycoproteins of goat epididymal maturing spermatozoa have been investigated using lectins as surface probes that interact with specific sugars with high affinity. Concanavalin A (ConA) and wheat-germ agglutinin (WGA) showed high affinity for mature cauda epididymal sperm agglutination, whereas RCA2, kidney beans lectin and peanut agglutinin caused much lower or little agglutination of the cells. The mature sperm exhibited markedly higher efficacy than the immature caput epididymal sperm for binding both ConA and WGA, as evidenced by sperm agglutination and the binding of the fluorescence isothiocyanate (FITC)-labelled lectins. FITC-ConA binds uniformly to the entire mature sperm surface whereas FITC-WGA binds to the acrosomal cap region of the head. The FITC-RCA2 mainly labelled the posterior head of mature cauda sperm. However, no WGA-specific glycoprotein receptors could be detected in sperm plasma membrane (PM) by WGA-Sepharose affinity chromatography. The data implied that the epididymal sperm maturation is associated with a marked increase in the ConA/WGA receptors and that WGA receptors may be glycolipids rather than glycoproteins. Analysis of the ConA receptors of cauda sperm PM identified by ConA-Sepharose affinity chromatography and subsequent resolution in SDS-PAGE demonstrated the presence of five glycopolypeptides of different concentrations (98, 96, 43, 27 and 17 kDa) of goat sperm membrane. The immunoblot of these ConA-specific glycopeptides with anti-sperm membrane antiserum showed that 98- and 96-kDa receptors are immunoresponsive.

N-glycolylneuraminic acid specific lectin from Pila globosa snail

A N-glycolylneuraminic acid-specific lectin (PAL) has been purified from an albumin gland extract of the apple snail, Pila globosa. Purification is conducted on a bovine submaxillary mucin-Sepharose 4B affinity matrix followed by gel filtration on a Sepharose 6B column. The lectin agglutinates rabbit erythrocytes. The hemagglutination activity is dependent on Ca2+ concentration in a significant manner but with a remarkable behaviour. The lectin is a trimeric glycoprotein of native Mr 440 kDa with 25% carbohydrate and is composed of three nonidentical subunits of molecular weights 190, 145, and 105 kDa. It has a pI of 7.0. The lectin exhibits a unique and strict specificity toward N-glycolylneuraminic acid and this phenomenon discriminates it from other known sialic acid binding lectins. The uniqueness indicates the absolute need for a glycolyl substitution on the amino residue and of a glyceryl side chain on the exocyclic part and an axial -COOH group in neuraminic acid. The presence of an acetyl substitution on the exocyclic part impedes lectin-ligand interaction.

Organization and localization to chromosome 5 of the human UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I gene

UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is a medial-Golgi enzyme essential for the synthesis of hybrid and complex N-glycans. We have isolated two overlapping genomic DNA clones which span 18 kilobases (kb) containing a single 2.5 kb exon for GlcNAc-T I. The exon includes most of the 5'-untranslated region, the complete coding sequence (1335 bases) for GlcNAc-T I (445 amino acids) and the complete 3'-untranslated region. The remaining exon (or exons) is at least 2.0 kb upstream of the intron-exon junction. Transient transfection of either clone into Lec 1 Chinese hamster ovary cell mutants (which lack GlcNAc-T I) indicates the presence of a promoter responsible for expression of a truncated transcript. Southern blot analysis indicates that the gene exists in single copy in the human genome and is located on chromosome 5. The human and rabbit enzymes are 85% similar at the nucleotide sequence level and 92% similar at the amino acid sequence level.

Immunoclinical correlation in diabetes mellitus. A preliminary report on the lectin-agglutination test

Twenty cases with insulin dependent diabetes mellitus (IDDM) were studied and compared with a control group with non insulin dependent diabetes mellitus (NIDDM) and another group of nondiabetic healthy persons. Lymphocytes of each group were tested for agglutination with three sets of lectins: concavalin A (ConA), soyabean agglutinin (SBA) and peanut agglutinin (PNA). SBA test, being highly positive in IDDM and persistently negative in NIDDM, is the most significant of the three tests for differentiating between the two types of diabetes mellitus.

Molecular cloning and expression of cDNA encoding the enzyme that controls conversion of high-mannose to hybrid and complex N-glycans: UDP-N-acetylglucosamine: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I

UDP-GlcNAc:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101) catalyzes an essential first step in the conversion of high-mannose N-glycans to hybrid and complex N-glycans. Cloning of the gene encoding this enzyme was carried out by mixed oligonucleotide-primed polymerase chain reaction amplification of rabbit liver single-stranded cDNA using sense and antisense 20- to 24-base-pair (bp) primers. A rabbit liver library in phage lambda gt10 yielded a 2.5-kilobase (kb) cDNA with a 447-amino acid coding sequence. None of the nine asparagine residues were in an Asn-Xaa-(Ser or Thr) sequence, indicating that the protein is not N-glycosylated. There is no sequence homology to other previously cloned glycosyltransferases, but GnT I appears to have a domain structure typical of these enzymes--i.e., a short amino-terminal domain, a transmembrane domain, a "neck" region, and a large carboxyl-terminal catalytic domain. RNA was transcribed off the 2.5-kb cDNA, and in vitro translation with rabbit reticulocyte lysate yielded a 52-kDa protein with GnT I activity.

In vitro effect of fluoroquinolones on theophylline metabolism in human liver microsomes

Some quinolone antibiotics cause increases in levels of theophylline in plasma that lead to serious adverse effects. We investigated the mechanism of this interaction by developing an in vitro system of human liver microsomes. Theophylline (1,3-dimethylxanthine) was incubated with human liver microsomes in the presence of enoxacin, ciprofloxacin, norfloxacin, or ofloxacin. Theophylline, its demethylated metabolites (3-methylxanthine and 1-methylxanthine), and its hydroxylated metabolite (1,3-dimethyluric acid) were measured by high-pressure liquid chromatography, and Km and Vmax values were estimated. Enoxacin and ciprofloxacin selectively blocked the two N demethylations; they significantly inhibited the hydroxylation only at high concentrations. Norfloxacin and ofloxacin caused little or no inhibition of the three metabolites at comparable concentrations. The extent of inhibition was reproducible in five different human livers. Inhibition enzyme kinetics revealed that enoxacin caused competitive and mixed competitive types of inhibition. The oxo metabolite of enoxacin caused little inhibition of theophylline metabolism and was much less potent than the parent compound. Nonspecific inhibition of cytochrome P-450 was ruled out since erythromycin N demethylation (cytochrome P-450 mediated) was unaffected in the presence of enoxacin. These in vitro data correlate with the clinical interaction described for these quinolones and theophylline. We conclude that some quinolones are potent and selective inhibitors of specific isozymes of human cytochrome P-450 that are responsible for theophylline metabolism. This in vitro system may be useful as a model to screen similar compounds for early identification of potential drug interactions.

Detection of HBsAg in newborns

Cord blood samples collected from 150 newborns were tested for HBsAg using micro ELISA technique. Only 8 (5.3 per cent) out of 150 samples were found to be positive for HBsAg in variable titres. It is important to identify these HBsAg positive newborns so that appropriate measures could be adopted at the earliest to prevent the complications of HBsAg carriage.

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.

Effect of lithium chloride on spermatogenesis, testicular delta 5- 3 beta- and 17 beta-hydroxysteroid dehydrogenase activities in toad (Bufo melanostictus)

The purpose of the present study was to show the effects of lithium on testicular activities in the toad. Adult male toads were injected with lithium chloride (200 micrograms/toad) of alternate days for 21 days. At the moment of sacrifice on 22nd day, lithium treated animal showed decreases in testicular weight and Leydig cell nuclear area along with inhibition of spermatogenesis and testicular delta 5-3 beta as well as 17 beta-hydroxysteroid dehydrogenase activities. The results of our present experiment suggest that lithium administration might be associated with significant adverse effects on testicular activity in toad.

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.

Differential effect of inflammation and dexamethasone on dolichol and dolichol phosphate synthesis

Inflammation and glucocorticoids stimulate hepatic glycoprotein synthesis, resulting in an increased secretion of serum glycoproteins. We now present evidence that the synthesis of dolichol and dolichol phosphate from mevalonate is increased in hepatocytes from inflamed rats. Also, in inflamed rats, the levels of dolichol and dolichol phosphate are increased in liver homogenates and microsomes. Dexamethasone treatment of the cells, however, does not increase the synthesis of dolichol and dolichol phosphate from mevalonate. The results suggest that the inflammation-induced dolichol-linked saccharide and glycoprotein synthesis is possibly mediated through an increase in the level of dolichol and dolichol phosphate in the liver. Since dexamethasone treatment does not increase the synthesis of dolichol and dolichol phosphate, its action on glycoprotein synthesis appears to be different and to affect the induction of enzymes in mannosyl phosphoryl dolichol- and dolichol-linked oligosaccharide synthesis.

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.