Thrombin inhibitory activity of some polyphenolic compounds.

Thrombin, also known as an active plasma coagulation factor II, belongs to the family of serine proteases and plays a crucial role in blood coagulation process. The process of thrombin generation is the central event of the hemostatic process and regulates blood coagulant activity. For this reason, thrombin inhibition is key to successful novel antithrombotic pharmacotherapy. The aim of our present study was to examine the effects of the well-known polyphenolic compounds on the activity of thrombin, by characterization of its interaction with selected polyphenols using different biochemical methods and biosensor BIAcore analyses. Only six compounds, cyanidin, quercetin, silybin, cyanin, (+)-catechin and (-)-epicatechin, of all examined in this study polyphenols caused the inhibition of thrombin amidolytic activity. But only three of the six compounds (cyanidin, quercetin and silybin) changed thrombin proteolytic activity. BIAcore analyses demonstrated that cyanidin and quercetin caused a strong response in the interaction with immobilized thrombin, while cyanin and (-)-epicatechin induced a low response. Lineweaver-Burk curves show that used polyphenol aglycones act as competitive thrombin inhibitors. Our results suggest that polyphenolic compounds might be potential structural bases and source to find and project nature-based, safe, orally bioavailable direct thrombin inhibitors.

Muscle FBPase in a complex with muscle aldolase is insensitive to AMP inhibition.

Real-time interaction analysis, using the BIAcore biosensor, of rabbit muscle FBPase-aldolase complex revealed apparent binding constant [K(Aapp)] values of about 4.4x10(8) M(-1). The stability of the complex was down-regulated by the glycolytic intermediates dihydroxyacetone phosphate and fructose 6-phosphate, and by the regulator of glycolysis and glyconeogenesis--fructose 2,6-bisphosphate. FBPase in a complex with aldolase was entirely insensitive to inhibition by physiological concentrations of AMP (I(0.5) was 1.35 mM) and the cooperativity of the inhibition was not observed. The existence of an FBPase-aldolase complex that is insensitive to AMP inhibition explains the possibility of glycogen synthesis from carbohydrate precursors in vertebrates' myocytes.

Identification of blood group A and B antigens in human glycophorin.

Glycophorin A (GPA), the major sialoglycoprotein of human erythrocyte membranes, was isolated separately from blood group A and B erythrocytes using phenol-water extraction. After purification, performed as gel filtration in the presence of SDS, two glycophorin samples GPA-A and GPA-B were run, in duplicate, in SDS-PAGE and electroblotted onto Immobilon P. After staining with 1) anti-glycophorin antibody and 2) with relevant anti-blood group (A or B) antibody it was shown that the band pattern of the samples in each duplicate was the same. GPA-A and GPA-B samples were also degraded using Carlson degradation (beta-elimination in mild alkaline/strong reducing conditions) and from reaction products the fractions of O-glycans and N-glycans were isolated; they were used in hemagglutination inhibition test. It was shown that both sugar fractions derived from GPA-A did inhibit agglutination of blood group A erythrocytes by anti-A antibody, whereas oligosaccharide fractions derived from GPA-B inhibited agglutination of blood group B erythrocytes by anti-B antibody. These results, obtained using immunochemical methods, confirm the presence of blood group A and B determinants in the carbohydrate moiety of human glycophorin, derived from the blood group A or B erythrocytes, respectively.

Isolation and characterization of glycophorin from nucleated (chicken) erythrocytes.

A sialoglycoprotein fraction was isolated from chicken erythrocytes by two methods based on the phenol extraction or chloroform/2-propanol extraction of differently prepared erythrocyte membranes. Both preparations gave in SDS-PAGE two major PAS-stained bands (GP2 and GP3), which migrated as 60- and 33-kDa species, respectively, compared to reference proteins, or as 44- and 23-kDa molecules, compared to human glycophorins. Some less abundant slower migrating PAS-stained components, antigenically related to GP2 and GP3, also were detected. No evidence for the presence of antigenically distinct glycoproteins of leukosialin type was obtained. Interconversion in SDS-PAGE, similar carbohydrate composition, and similar antigenic properties of GP2 and GP3 indicated that they are a dimer and monomer, respectively, of the same glycoprotein which shows properties that allow it to be classified as a glycophorin. Lectin binding studies and methylation analysis of beta-elimination products of chicken glycophorin preparation showed the presence of O-glycans and N-glycans. The major O-glycans include sialylated Galbeta1-3GalNAc units and more complex GlcNAc-containing chains. Among the N-glycans, there are complex-type biantennary structures with a bisecting GlcNAc residue, accompanied by chains with additional antennas linked to alpha-mannose residues. A characteristic feature of the chicken glycophorin is a relatively high proportion of N-glycans to O-glycans, compared to the glycophorin A from human erythrocytes.

Carbohydrate moiety of immunoglobulins in health and pathology.

Most of glycoproteins described so far, including immunoglobulins, are glycosylated during post-translational modifications of protein molecules. Current knowledge of the structure of sugar chains in immunoglobulin molecules and their biological role in health and pathology is reviewed.

The carbohydrate moiety of human glycophorin in CDG syndrome.

Human glycophorin, the major sialoglycoprotein of erythrocyte membranes, was isolated from erythrocytes of healthy individuals and four patients with CDG syndrome. Sugar analysis revealed lower carbohydrate content in three out of four CDG-glycophorin samples. In order to characterize closer the glycosylation differences between glycophorin samples in health and disease, reaction with four biotinylated lectins was performed, using ELISA procedure on polystyrene microplates. Results obtained so far strongly suggest that both N- and O-glycans of glycophorin are affected in CDG syndrome.

Glycosylation of bile-salt-stimulated lipase from human milk: comparison of native and recombinant forms.

Bile-salt-stimulated lipase (BSSL) is an enzyme present in human milk. BSSL is important for fat digestion in infants. It contains one site for N-glycosylation and a serine/threonine-rich domain which is highly O-glycosylated. Both N- and O-linked sugar chains were studied on native BSSL from three donors and compared to the glycosylation of recombinant BSSL produced in Chinese hamster ovary or mouse fibroblast (C-127) cell lines. The carbohydrate composition of oligosaccharides was mapped using sugar and methylation analyses, enzyme-linked immunosorbant assay, and different separation techniques. Native BSSL was found to be highly glycosylated (19-26%). It contained a high amount of fucosylated oligosaccharides and expressed both Lewis a and Lewis b blood group antigens. None of the recombinant BSSL forms contained fucose. N-linked structures on native BSSL were identified as mainly mono- and disialylated biantennary complex type structures with or without fucose substitution. High-pH anion-exchange chromatography analysis indicated that the recombinant forms of BSSL contained similar types of N-glycan structures differing mainly in their content of sialic acid and by the absence of fucose residues. Native BSSL contained predominantly large O-linked oligosaccharides. This was in contrast to the recombinant forms of BSSL which contained mainly short type O-glycans with a high content of sialic acid. Interestingly, the estimated number of O-glycans attached to native BSSL was lower than that for the recombinant forms.

Blood group MN-dependent difference in degree of galactosylation of O-glycans of glycophorin A is restricted to the GalNAc residues located on amino acid residues 2-4 of the glycophorin polypeptide chain.

Glycophorin A (GPA) of human erythrocytes contains a minor number of unsubstituted GalNAc residues (Tn receptors) which are recognized by Moluccella laevis lectin (MLL). The lectin reacts better with blood group N- than M-type of GPA which suggests a higher number of Tn receptors in GPA-N than in GPA-M. To find out whether this difference is restricted to a defined domain of GPA, the N-terminal tryptic glycopeptides of GPA-M and GPA-N (a.a. residues 1-39) and their fragments obtained by degradation with CNBr (a.a. residues 1-8 and 9-39) were analyzed. The untreated and desialylated glycopeptides were tested as inhibitors of MLL in ELISA, and the content of GalNAc-ol was determined in the products of beta-elimination of the asialoglycopeptides by gas-liquid chromatography/mass spectrometry. The asialoglycopeptides 1-39 and 1-8 derived from GPA-N showed about 2 and 4 times higher content of non-galactosylated GalNAc residues, respectively, and higher reactivity with MLL than their counterparts derived from GPA-M, while asialoglycopeptides 9-39 of GPA-M and GPA-N did not show such differences. These results demonstrate that higher expression of non-galactosylated GalNAc in GPA-N than in GPA-M is confined to GalNAc residues located in the amino-terminal portion of GPA polypeptide chain, between the blood group M- and N-specific amino acid residues 1 and 5.

Determination of single monosugars bound to a peptide.

A method is described which allows detection and quantitative determination of single monosugar units bound O-glycosidically to a peptide. A glycoprotein or a glycopeptide is chemically degraded under the modified conditions of Carlson degradation (beta-elimination performed in weakly alkaline conditions in the presence of sodium borohydride). An aliquot of the neutralized reaction mixture, supplemented with an internal standard, is peracetylated, extracted and directly analyzed by g.l.c.-m.s. All the O-linked oligosaccharides split off from the peptide are derivatized, but under gas-liquid chromatography at 150-230 degrees C only monosugar peracetylated alditols reach the detector. By comparing the retention times of appropriate peaks with standards and by checking their mass spectra the monosugar alditols are unequivocally identified. The detectable amount of a reduced monosugar in the analyzed sample is about 0.3 microgram. Several glycoproteins were analyzed using this method. Free N-acetylgalactosaminitol was detected in the degradation products of human glycophorin A and ovine submaxillary mucin, additionally free galactitol was detected in the degradation products of glycophorin. This result suggests that some single galactose units, O-glycosidically linked to the peptide are present in human glycophorin A.

Evidence for glycosylation of the juvenile-hormone-binding protein from Galleria mellonella hemolymph.

The juvenile-hormone-binding protein (JHBP) from Galleria mellonella hemolymph, which is a member of the high-affinity/low-molecular-mass group of JHBP proteins, was found to be glycosylated. Glycosylation was confirmed by the following evidence. Carbohydrate gas-liquid chromatography analysis of the purified JHBP preparations showed the presence of a low amount of sugars (Man and GlcNAc were the major components). The JHBP electrophoretic band blotted onto nitrocellulose was stained with GlycoTrack (a reagent kit used for the detection of protein glycosylation) and showed strong binding of concanavalin A (ConA). JHBP was fractionated on a ConA-Sepharose 4B column into ConA-bound (strongly stained with ConA) and ConA-unbound (hardly stained with ConA) portions. Both fractions showed juvenile-hormone-binding activity and were glycosylated, as revealed by staining both of them with GlycoTrack. Electrospray-ionization mass spectrometry of JHBP suggested the presence of a small amount of presumably nonglycosylated protein (24988 Da) and five glycoforms, two of which (containing Man2GlcNAc, or Man2Fuc1GlcNAc2 chain) were not bound or were weakly bound to ConA, and three (with Man3GlcNAc2, Man5Fuc1GlcNAc2, or Man5GlcNAc2, chain) were present in the fraction strongly bound to ConA. In conclusion, the monosugar composition, GlycoTrack staining, ConA-binding properties and molecular mass analyses of JHBP supplied convincing evidence for its glycosylation and some information on the character of the oligosaccharide chains.

Subtle differences in glycosylation of blood group M and N type glycophorin A detected with anti-Tn lectins and confirmed by chemical analysis.

A higher content of Tn and sialyl-Tn receptors in glycophorin A of blood group N than in that of blood group M was suggested by reactions with anti-Tn lectins. Analysis of beta-elimination products of two blood group M and two blood group N preparations by gas liquid chromatography-mass spectrometry showed that GalNAc-ol was detectable in minor amounts in all analyzed samples and its content was higher in the products obtained from desialylated antigens. Moreover, the content of GalNAc-ol detected in blood group N samples was almost twice as high as in respective blood group M samples. Since blood group M and N antigens differ in two amino-acid residues, our results support the existence of sequence-dependent differences in efficiency of substitution of glycophorin GalNAc-Ser/Thr residues with galactose.

Mouse monoclonal IgA antibodies lack interchain disulfide bonds.

A mouse monoclonal IgA antibody (A008), anti-blood group A antigen, was shown to dissociate into heavy (H) and light (L) polypeptide chains under non-reducing conditions. The dissociation occurred in the presence of 0.2% sodium dodecyl sulphate (2 h at room temperature) or at elevated temperature (1 h at 70 degrees C). The free H and L polypeptide chains could be separated in SDS-polyacrylamide gel electrophoresis or by gel filtration in the presence of SDS. The dissociation of IgA (A008) antibody into heavy and light polypeptide chains was reversible, since the fractions containing gel filtration-isolated chains, after removing the detergent, pooling together and incubation at 4 degrees C created again the immunoglobulin molecules with activity close to the native value. Similarly, the same IgA antibody heated at 70 degrees C for 1 h recovered its antibody activity after keeping at 4 degrees C. Three other mouse monoclonal IgA antibodies showed the same ability to dissociate into heavy and light polypeptide chains after exposure to SDS or elevated temperature, which suggests that this outstanding property is a characteristic feature of the mouse monoclonal IgA antibodies and it comes out from the lack of H-H, L-L and H-L interchain disulfide bonds in these molecules.

An improved approach to the analysis of the structure of small oligosaccharides of glycoproteins: application to the O-linked oligosaccharides from human glycophorin A.

Treatment of purified human glycophorin A with alkaline borohydride cleaved the oligosaccharide side chains to yield alditol derivatives that were separated by gel filtration into three mixtures of low molecular weight compounds. Each mixture was oxidised with periodate, and the products were reduced with borohydride and analysed after acetylation or methylation by GLC-MS and FABMS. The resulting data allowed the monosaccharide sequence and linkage positions to be assigned to each component of the mixtures. The anomeric configuration was determined by 1H NMR spectroscopy of the intact fractions. The structures of a desialylated tetrasaccharide, two monosialylated trisaccharides, and five other minor products were defined.

Investigation of the structural heterogeneity in the carbohydrate portion of a mouse monoclonal immunoglobulin A antibody.

A mouse immunoglobulin A monoclonal antibody was isolated from hybridoma culture fluid by affinity chromatography. Chemical analysis of the intact antibody showed a monosaccharide composition, which besides mannose also contained monosaccharides commonly found in N-linked complex type of carbohydrate structures. No N-acetylgalactosamine was found showing the absence of O-linked oligosaccharides. The carbohydrate chains were released from the polypeptide and after fractionation on immobilized concanavalin A and high-performance ion-exchange chromatography structural analysis was performed. The structures were determined by chemical analyses, periodate oxidation in combination with fast atom bombardment mass spectrometry, and 500 MHz 1H NMR spectroscopy. The data revealed a great structural heterogeneity, including partially sialylated bi- and triantennary type of structures. Both types contained in addition species with branches terminated by Gal alpha 1-3Gal sequences.

Structural analysis of the N-linked oligosaccharides from murine glycophorin.

Glycophorins, isolated from BALB/c mouse erythrocytes, were degraded under mild and strong reductive alkaline conditions and the N-linked oligosaccharides were isolated as alditols. The oligosaccharide alditols were fractionated and purified using gel filtration, concanavalin A-Sepharose affinity chromatography, and high-performance ion-exchange chromatography. Structural analysis was carried out by chemical analyses, periodate oxidation in combination with fast atom bombardment mass spectrometry, and 500-MHz 1H NMR spectroscopy. The results revealed the presence of sialylated biantennary, triantennary, and tetraantennary complex type oligosaccharides, all fucosylated at the innermost N-acetylglucosamine residue. The tri- and tetraantennary oligosaccharide-containing fractions also contained species elongated by one and/or two N-acetyllactosamine (-3Gal beta 1-4GlcNAc beta 1-) sequences. The N-linked oligosaccharides were shown to be combined only with one (the low molecular weight) of the two mouse glycophorins.

The carbohydrate structures of a mouse monoclonal IgG antibody OKT3.

A mouse monoclonal antibody OKT3, of IgG2a isotype, was isolated from hybridoma culture fluid. Sugar analysis showed the presence of sialic acid, galactose, mannose, fucose, and N-acetylglucosamine, i.e. sugars typical for N-glycosidically linked carbohydrate chains. The absence of N-acetylgalactosamine revealed that O-glycosidically linked carbohydrates were not present. The purified antibody was reduced, alkylated, and separated into heavy and light chains, and all carbohydrates were shown to be associated with the heavy chains. The N-linked carbohydrate chains were isolated as alditols using strong alkaline-borohydride degradation and further fractionated on a concanavalin A-Sepharose column and high performance ion exchange chromatography with pulsed amperometric detection. Structural analysis was carried out on the isolated oligosaccharide alditols by chemical analyses, fast atom bombardment mass spectrometry, and 500-MHz 1H NMR spectroscopy. Triantennary and biantenary types of structures were found. The triantennary structures were present as trisialo and tetrasialo forms without fucose; the tetrasialo forms were shown to contain a sequence of Neu5Ac alpha 2-3Gal beta 1-3[Neu5Ac alpha 2-6]GlcNAc beta 1- on one of the branches. The biantennary structures were present as completely sialylated nonfucosylated species and as asialo-, agalacto-, and partially fucosylated structures.

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).

Mouse erythrocyte membrane sialoglycoproteins and their involvement in the interaction with mouse rosette forming human lymphocytes.

Sialoglycoproteins were isolated from Balb/c mouse erythrocyte membranes. The crude preparation showed four PAS-positive zones in SDS-polyacrylamide gel electrophoresis. The lowest molecular weight component was separated on the Ultrogel AcA44 column in the presence of SDS. The carbohydrate composition of the fractions obtained indicated that the sialoglycoproteins contained O-glycosidic oligosaccharide chains and and that the lowest molecular weight glycoprotein also contained N-glycosidic chain(s). The sialoglycoproteins strongly and specifically inhibited the rosette formation between mouse erythrocytes and human B lymphocytes. It suggested that sialoglycoproteins were the mouse red cell components involved in the interaction with human lymphocytes.