Identification and isolation of an agglutinin from uterus of rats

Purification of Two Novel Sugar Acid-binding Lectins from Haplomitrium Mnioides (bryophyte, Plantae) and their Preliminary Characterization

Two novel sugar acid-binding lectins were purified from Haplomitrium mnioides (Lindb.) Schust. using a procedure consisting of ammonium sulfate precipitation, G-50 gel filtration, hydroxyapatite chromatography, and HW-50 gel filtration. We reported their partial physicochemical properties: molecular weight, affinity for carbohydrates and organic acids, pH stability, and dependence of their hemagglutination activity on metal ions. We also determined their N-terminal amino acid sequences. H. mnioides lectins (HMLs) were monomers (one with a molecular weight of approximately 27 kDa, and the other with a molecular weight of approximately 105 kDa) under both nonreducing and reducing conditions. They were named HML27 and HML105, respectively. Both HMLs had an affinity for N-acetylneuraminic acid, D-glucuronic acid, D-glucaric acid, bovine submaxillary mucin, heparin, and organic acids, such as citrate, 2-oxoglutaric acid, and D-2-hydroxyglutarate. Furthermore, HML27 had an affinity for α-D-galacturonic acid, D-malate, L-malate, and pyruvate, while HML105 had an affinity for D-gluconic acid. HML27 and HML105 are novel plant lectins: they have an affinity for sugar acids and organic acids and specifically recognize the carboxyl group, and there is no homology between their N-terminal amino acid sequences and those of the previously described lectins and agglutinins.

Sialic acid binding protein of human endometrium: its regulation by steroids

In the present study, we have observed that sialic acid binding protein (SABP - a 54 kDa glycoprotein which was isolated from human endometrial scrapings taken at various stages of the menstrual cycle from normal cycling females and purified to apparent homogeneity and was earlier reported from this laboratory) was found in sufficiently detectable amount in the endometrium of normal cycling women whereas it was found in lesser amount in tissue from women who have recently entered the postmenopause stage. SABP was observed in both follicular and luteal phase of menstrual cycle which was found by western blot analysis. In the de-novo synthesis experiment, synthesis and secretion of SABP was found to be stimulated by estradiol (E2) whereas progesterone (P4) was found to have no significant stimulatory effect on it which was also confirmed by HEC cell culture. In the HEC cell culture, priming of cells with E2 was found to influence the effect of P4 on SABP when it was added 2 h after E2 administration. This was observed by doing immunoprecipitation followed by SDS-PAGE and autoradiography. Hence this report clearly indicates that E2 regulates the synthesis and secretion of 54 kDa SABP from human endometrium. How E2 priming of endometrium influences the effect of P4 on SABP has been discussed.

Paracrine effects of a uterine agglutinin are mediated via the sialic acids present in the rat uterine endometrium

A 32 kDa estrogen-induced, sialic acid-specific agglutinin (P-SAS) was isolated from rat endometrium in its proestrus stage. To investigate the functional importance of P-SAS in the uterine milieu, specific binding assays were carried out with 125I-labeled P-SAS and different cellular components of the uterus (epithelial, stromal and myometrial cells), that were isolated from different stages of the estrus cycle. The results indicate that although the protein is secreted from the epithelial cells in the estrogenic phase, it binds specifically to the stromal cells, especially to those isolated from the diestrus stage of the estrus cycle. The specific binding, however, is seen to decrease with the progression of pregnancy. Scatchard analysis performed with varying amounts of 125I-P-SAS in the presence of excess cold P-SAS revealed that the binding occurs with a Ka = 1.69 x 10(8) M(-1). As P-SAS binds specifically to sialic acids on the stromal cell surface, further characterization of the sialic acid molecule to which P-SAS binds was carried out by gas liquid chromatography (GLC). The studies revealed that P-SAS preferentially binds to N-glycolylneuraminic acid, which is attached to the penultimate sugar of the stromal cell surface glycoprotein chain via alpha2,6 linkage. As P-SAS is further known to be mitogenic, the effect of P-SAS on cultured stromal cells was studied in vitro. The growth regulatory assays revealed that P-SAS induced 3H-thymidine uptake by stromal cells in culture. Thus, from the above observations, paracrine effects of P-SAS on the stromal cells and on the subsequent growth and development of the uterus can be assumed.

Histochemical studies on sialic acids in the epididymis during post-natal development of the rat

A variety of sialic acids contained in the rat epididymis during post-natal development were examined by means of lectin and carbohydrate histochemistry. Epididymides from male Sprague-Dawley rats on post-natal days 14, 21, 30, 39, 49, 56 and 70 were fixed in Bouin's fluid and embedded routinely in paraffin wax. Hydrated sections were subjected either to the lectin methods using biotinylated Sambucus sieboldiana lectin or Maackia amurensis lectin or to the selective periodate oxidation-phenylhydrazine-thiocarbohydrazide-silver protein-physical development technique with or without saponification. The results revealed that sialic acids appeared in the epididymal epithelium at day 14, followed by particular distribution patterns corresponding to cell differentiation during days 21-39. High-level O-acetylation of sialic acids was observed in the principal cells of the initial segment and proximal caput after day 39. These results suggest that sialic acids with different linkages and O-acetylation become adult in distribution at the 'differentiation' period under the influence of androgen, before spermatozoa reach the epididymal lumen. Such carbohydrates may be correlated, at least in part, with sperm-binding sialoproteins, which increase dramatically during the window between days 21 and 39.

Modulation of sialic acid-binding proteins of rat uterus in response to changing hormonal milieu

A group of sialic acid binding (SAS) agglutinins has been isolated from the rat uteri at different stages [Proestrus (P), estrus (E) and diestrus (D)] of estrous cycle. Studies of biochemical properties indicate that SAS agglutinins are glycoprotein in nature having molecular weights between 28-31 Kd and microheterogenous pI. Function-based characterization revealed that inspite of the fact that all three proteins exhibit sialic acid binding property, the sialic acid binding affinities, calculated from Scatchard analysis, using 4-methylumbelliferyl sialic acid as a ligand, varied in stage specific manner (Ka:D-SAS-9.03 x 10(5) M-1, P-SAS-2.33 x 10(5) M-1, E-SAS-2.13 x 10(5) M-1). Circular dichroism spectra of these three agglutinins suggested that differences exist in the secondary structures of the proteins isolated from different stages. Removal of carbohydrate moiety by trifluoromethane sulfonic acid treatment and CNBr cleavage studies showed some homology between these proteins, however, the variation in the carbohydrate moiety was apparent from the sugar analysis data. Functionally and immunologically these proteins can be grouped as estrogenic and progestogenic SAS agglutinins.

Hormonal regulation of sialic acid-binding (SAS) protein synthesis of rat uterus

Sialic acid binding proteins (SAS) of rat uteri have been found in all three stages of the estrous cycle. To study the control of synthesis of these proteins two different animal models were used I-immature female rats (25 d) where the hormones estradiol (E2) and progesterone (P4) were given separately and together, and II-adult female rats where hormone treatment commenced 14 days after ovariectomy. The data indicated that E2 initiated the synthesis of SAS proteins in the immature animals, while P4 could inhibit SAS synthesis, either given alone or together with E2. However, prior priming of the rat with E2 and subsequent administration of P4 stimulated SAS protein synthesis.

Albumen gland of the snail Achatina fulica is the site for synthesis of AchatininH, a sialic acid binding lectin

A sialic acid binding lectin, AchatininH was purified from the hemolymph of Achatina fulica snail. To identify the site of synthesis of AchatininH, in vitro incubation studies in presence of labelled amino acid precursor were performed. Different organs from the snail were sliced and incubated in methionine-deficient Eagle's minimum essential medium containing [35S]-methionine at 25 degrees C for 5 h. After termination of incubation, tissues were homogenized, centrifuged and the de novo synthesized protein was immunoprecipitated with specific AchatininH antibody, followed by protein-A. The precipitated antigen-antibody complex was analysed by SDS-PAGE. Data obtained from native gel electrophoresis and SDS-PAGE radioautographic analysis indicates that AchatininH is synthesized in the albumen gland.

Carbohydrate-binding specificity of calcyclin and its expression in human tissues and leukemic cells

Binding of biotinylated fetuin in a solid-phase assay served as activity assay for purification of calcyclin, the product of a cell growth-related cDNA with homologies to Ca(2+)-binding proteins. Asialofetuin failed to bind to calcyclin, emphasizing the importance of sialic acids. Binding of fetuin was most effectively reduced by N-glycolylneuraminic acid within a panel of mostly negatively charged sugars. Bovine submaxillary mucin and the ganglioside GM1, but not asialo-GM1, proved more effective than neoglycoproteins, carrying negatively charged carbohydrate moieties. Extension of N-acetyl-neuraminic acid to its lactosyl derivative increased its inhibitory potency. Among charge-free carbohydrate residues, only N-acetylglucosamine, lactose, and mannose, but not fucose, melibiose, or N-acetylgalactosamine affected fetuin binding, substantiating the inherent selectivity. Chemical modification with group-specific reagents revealed that lysine and arginine residues appear to be involved in ligand binding that is optimal in the presence of Ca2+, but not Zn2+ and stable up to 1 m NaCl. Biotinylation of calcyclin by modification of carboxyl groups facilitated performance of solid-phase assays with calcyclin in solution, yielding similar results with (neo)glycoproteins in relation to assays with immobilized calcyclin, thereby excluding an impact of binding to nitrocellulose on calcyclin's specificity. Subcellular fractionation disclosed the presence of fetuin-binding activity in all fractions, the specific activity decreasing from the nuclear to the particulate cytoplasmic fraction and the cytoplasmic supernatant. Affinity-purified antibodies were employed to detect high levels of calcyclin expression in acute lymphoblastic, myelogenous, and monocytic leukemia cell lines, but not in myeloma or lymphoblastoid cells. In comparison, most cells were nearly devoid of an O-acetylsialic acid-specific protein that is more abundant in various tissue types than calcyclin.

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.

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.

Identification of a cell cycle-dependent gene product as a sialic acid-binding protein

A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein.

Functional heterogeneity of sialic acid binding agglutinins of rat uteri towards in vitro lymphocyte transformation

The sialic acid binding agglutinins (SAS) are purified from three different stages (proestrus [P], estrus [E], diestrus [D]) of rat uterine homogenate. All three proteins are capable of inhibiting the in vitro phytohemagglutinin (PHA)-induced blastogenic response of lymphocytes and thymocytes as manifested by inhibition of 3H-thymidine incorporation into cells. The lymphocytes isolated from pregnant female rats were found to be more susceptible to inhibition. In resting lymphocyte cultures (RLC), however, the P- and E-SAS proteins acted differently from the D-SAS by stimulating lymphocyte proliferation in the cultures initiated from normal rat lymphocytes. At the same dose these proteins were inhibitory to the RLC, where cultured lymphocytes were isolated from the pregnant female. Reverse hemolytic plaque formation assay results also indicated functional heterogeneity between these proteins. P-SAS induced a potent polyclonal activation of the B cell, whereas E- and D-SAS did not show much activation. SAS proteins do not have any complement-like activity. These results, corroborated by cell viability count and 51Cr uptake tests, suggest that D-SAS has genuine lymphoblastogenesis-suppressive properties whereas P- and E-SAS-induced suppression in the presence of PHA is probably due to an increased cell-density-dependent cytotoxicity.

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.

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.

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.

Differential expression of endogenous sugar-binding proteins (lectins) in murine tumor model systems with metastatic capacity

In order to investigate possible differences in sugar binding activities of strongly versus weakly metastatic tumors, sugar-binding molecules (endogenous lectins) of murine tumor cells differing in metastatic capacity were analyzed by affinity chromatography on supports with immobilized sugars or glycoproteins and compared. After elution with specific sugar in the absence of Ca2+-ions, the proteins were separated by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. In comparison to a weakly metastatic subline (Eb) spontaneous strongly metastatic variants (ESb) of a murine lymphoma contained additional sugar receptors for N-acetylglucosamine (Mr 30 kDa) and maltose (Mr 64 kDa, 62 kDa, 54 kDa and 32 kDa), and lacked one sugar receptor for myoinositol (Mr 85 kDa), N-acetylglucosamine (Mr 23 kDa) and maltose (Mr 22 kDa), respectively. The strongly metastatic variant ESb expressed the common beta-galactoside-specific lectin to a higher extent and receptors for myo-inositol, melibiose and mannan to a lower extent. In another model system derived from the murine mastocytoma cell line P 815 X 2A, biochemical analysis of the liver-metastasizing variant P 815 X 2B revealed additional characteristic N-acetylgalactosamine- and maltose-specific binding proteins. This variant had reduced amounts of receptors for beta-galactosides and fucose in comparison to the parental clone. In a third tumor system a similar qualitative difference was disclosed: a metastatic variant derived from spleen metastases displayed a sugar receptor profile with 5 additional beta-galactoside-binding proteins when compared to its parental clone 6-6#3 + F, which is a virally transformed fibroblast line. The results show that metastatic variants of 3 murine tumor models consisting of lymphomas, mastocytomas and sarcomas are characterized by qualitative and quantitative alterations in the profiles of sugar-binding proteins.

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.

Isolation of a keto sugar specific agglutinin from rat uterus

A ketosugar-specific agglutinin has been identified and purified to apparent homogeneity by affinity chromatography from the three days post-coital rat uterus. This protein is not found in other stages of estrous cycle. The agglutinin is glycoprotein, moves as single band with molecular weight 37,000 in polyacrylamide gel electrophoresis and pI is 4.2. Among the ketosugars, fructose and ribulose effectively inhibit the agglutinin activity, beside these sugars, mannose, glucose, alpha methyl-mannoside and glucoside are also effective as potent inhibitors. Possible roles of this protein in pregnancy are discussed.