Types Of Carbohydrate Chains Research Articles

Subunit structures of three human myeloperoxidases.

The heavy and the light subunits of human myeloperoxidase (donor: H2O2 oxidoreductase [EC 1.11.1.7]) I, II, and III were isolated from the reduced and S-carboxymethylated enzymes. These three enzymes have the same terminal amino acid sequences and similar chemical compositions in both subunits. The NH2-terminal sequences of the heavy and light subunits were determined to be Val-Asn-Cys-Glu-Thr- and Thr-Cys-Pro-Glu-Gln-, respectively; a heterogeneity was observed in the NH2-termini of the latter subunits for the three enzymes. As for COOH-termini, the sequences -(Asn, 2 Leu, Ala, Ser, Trp)-Arg-Glu-Ala and -Ala-Arg were obtained for the heavy and the light subunits, respectively. The heavy subunits contained 8-10 mol/mol of glucosamine. On the basis of these results and the amino acid sequence deduced from cDNA clones, the heavy subunits probably correspond to amino acids 279-744 and the light subunits to amino acids (164-167)-272. For the heavy subunits, Ser-745, which was predicted as the COOH-terminal amino acid from the nucleotide sequence, was removed. The light subunits were also processed at their COOH-termini by 6 residues. Four or five high mannose type carbohydrate chains were attached to the heavy subunits.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases.

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.

The mammalian beta-adrenergic receptor: structural and functional characterization of the carbohydrate moiety.

Mammalian beta-adrenergic receptors are glycoproteins consisting of a single polypeptide chain of Mr approximately 64,000. Treatment of purified [125I]-labeled hamster lung beta-adrenergic receptor with alpha-mannosidase reveals two discrete populations of receptor consistent with previous studies using membrane bound photoaffinity-labeled receptor. Treatment of the [125I]-labeled receptor with endoglycosidase F results initially in the formation of a Mr approximately 57,000 peptide which is further converted to Mr approximately 49,000 suggesting that there are two N-linked carbohydrate chains per receptor polypeptide. Exoglycosidase treatments and lectin chromatography of the [125I]-labeled receptor reveals the presence of two complex type carbohydrate chains (approximately 10% of which are fucosylated) on approximately 45% of the receptors. The remaining approximately 55% of the receptors appear to contain a mixture of carbohydrate chains (possibly high mannose, hybrid and complex type chains). Deglycosylation of the receptor by endoglycosidase F does not appear to alter the binding affinity of the receptor for a variety of beta-adrenergic agonists and antagonists. Moreover, the ability of control, alpha-mannosidase sensitive or insensitive (fractionated on immobilized wheat germ agglutinin) and neuraminidase, alpha-mannosidase or endoglycosidase F treated receptors to interact with the stimulatory guanine nucleotide regulatory protein in a reconstituted system were virtually identical. The deglycosylated receptor was also unaltered in its heat lability as well as its susceptibility to a variety of proteases. These findings demonstrate that the carbohydrate portion of the beta-receptor does not contribute to determining either its specificity of ligand binding or coupling to the adenylate cyclase system.

Glycosylation of the bovine coronavirus hemagglutinin protein.

The bovine coronavirus hemagglutinin protein gp140 is composed of disulfide-linked subunits of 65 kDa. This protein was further characterized with regard to its glycosylation. The glycosylated subunits of the protein are polypeptides having a molecular mass of 42.5 kDa. Both subunits appear to be processed to the same extent by the addition of N-linked oligosaccharides. Each subunit on the mature virion has 6-7 high mannose and 3-4 complex type carbohydrate chains attached to it.

Mammalian beta-adrenergic receptors. Distinct glycoprotein populations containing high mannose or complex type carbohydrate chains.

Mammalian beta-adrenergic receptor binding peptides can be visualized by covalently labeling them with the photoaffinity reagent p-azido-m-[125I]iodobenzylcarazolol followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The receptor peptides migrate as broad bands of Mr approximately equal to 62,000. In the present study, we examined the carbohydrate composition of the mammalian beta receptor through the use of specific exo- and endoglycosidases and lectin affinity chromatography. Treatment of p-azido-m-[125I]iodobenzylcarazolol-labeled beta2-adrenergic receptors from hamster lung or rat erythrocyte with the exoglycosidases neuraminidase and alpha-mannosidase provided evidence for the existence of both high mannose and complex type carbohydrate chains on beta 2-adrenergic receptors. The nonadditivity of the effect of sequential treatments with these enzymes suggested discrete populations of beta-adrenergic receptors containing either complex or high mannose type chains. Deglycosylation of receptor with endoglycosidase F results in a single labeled polypeptide at Mr = 49,000 for both systems. The same two populations of the beta receptors (high mannose or complex type chain) could also be fractionated by lectin affinity chromatography of solubilized p-azido-m-[125I]iodobenzylcarazolol-labeled receptors. The high mannose-containing receptors could be absorbed to and specifically eluted from concanavalin A-agarose. Those containing complex type carbohydrates could be adsorbed to and eluted from wheat germ agglutinin-agarose. Taken together, these data suggest that mammalian beta-adrenergic receptors contain both complex and high mannose type carbohydrate chains and that microheterogeneity of these chains likely explains the broad band pattern typically obtained on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Retinoic acid alters the proportion of high mannose to complex type oligosaccharides on fibronectin secreted by cultured chondrocytes.

Fibronectin synthesized by retinoic acid-treated chondrocytes exhibits a higher apparent subunit molecular weight in sodium dodecyl sulfate-polyacrylamide gels than fibronectin from untreated cultures. Analyses of peptide fragments show that retinoic acid treatment alters the apparent molecular weight of the collagen-binding fragment. Approximately one-sixth of the carbohydrate moieties on the collagen-binding fragment from control chondrocytes were sensitive to endo-beta-N-acetylglucosaminidase H, whereas the collagen-binding fragment from treated chondrocytes was more resistant to endo-beta-N-acetylglucosaminidase H. These findings indicate that chondrocyte fibronectin contains oligosaccharides of the high mannose or hybrid type in contrast to fibroblast fibronectin which only contains complex type carbohydrate chains and that retinoic acid treatment results in a higher proportion of complex type carbohydrate chains on chondrocyte fibronectin.

Estimating glycoprotein carbohydrate chain structures by lectin reactivities in polyacrylamide gels.

Complex mixtures of cellular glycoproteins contain a myriad of different carbohydrate chains that cannot be easily analyzed without rigorous purification of each individual glycoprotein. We have analyzed the carbohydrate chains in complex mixtures of cellular glycoproteins by separation using sodium dodecyl-sulfate polyacrylamide gel electrophoresis and interacting the gels with several 125I-labeled lectins. By use of in situ chemical modifications of the glycoproteins after their electrophoretic separation together with the known carbohydrate-binding specifities of several lectins, it has been possible to estimate glycoprotein carbohydrate chain structures. As an example we have examined the cellular glycoproteins of a ovary-colonizing metastatic variant of B16 melanoma and report the types of carbohydrate chains that are found on various melanoma glycoproteins.

Interaction of pokeweed mitogen with poly( N-acetyllactosamine)-type carbohydrate chains

The carbohydrate-binding specificities of pokeweed mitogen (PWM) were studied by interaction between 125I-PWM and purified glycoproteins. Human erythrocyte-membrane, band-3 glycoprotein bound 125I-PWM, but other glycoproteins containing triple-branched (tri-antennary)-complex-, double-branched (bi-antennary)-complex-, hybrid-, high-mannose, or small-mucin-type carbohydrate chains failed to bind 125I-PWM. Pretreatment of human erythrocytes with endo-β- d-galactosidase prevented 125I-PWM binding to the erythrocytes, as well as to band-3 glycoprotein from these cells. Poly( N-acetyllactosamine) glycopeptides and complex-type glycopeptides purified from band-3 glycoprotein and porcine thyroglobulin, respectively, were labeled at their nonreducing, terminal d-galactosyl or 2-acetamido-2-deoxy- d-galactosyl groups by d-galactose oxidase-sodium borotritide treatment and examined for interaction with agarose-immobilized PWM isolectins. From the binding behavior of these labeled glycopeptides on columns of immobilized-PWM isolectins, and from the interaction of various glycoproteins bearing known carbohydrate chains with 125I-PWM, it was concluded that all three major PWM isolectins (Pa-1, Pa-2, and Pa-4) bind specifically to poly( N-acetyllactosamine) structures.

Uniformity of glycans within molecular variants of alpha-protease inhibitor with distinct affinity for concanavalin A.

Human alpha 1-protease inhibitor contains four asparagine-linked carbohydrate chains per molecule. Three types of carbohydrate chains were released from the polypeptide backbone by hydrazinolysis: (a) biantennary (80%), (b) biantennary with an intercalated N-acetylglucosamine residue (14%), and (c) triantennary (6%). Using concanavalin-A-affinity chromatography, native and S-carboxymethylated alpha 1--protease inhibitor were fractionated into three distinct molecular variants which were shown to contain only one type (a, b, or c, respectively) of glycan per molecule. This and previous observations on other serum glycoproteins support the proposal of uniformity of glycan type within individual molecular variants of glycoproteins.

Glycosylation sites of influenza viral glycoproteins: characterization of tryptic glycopeptides from the A/USSR(H1N1) hemagglutinin glycoprotein.

Glycosylated tryptic peptides of the hemagglutinin (HA) glycoprotein of influenza A/USSR/90/77(H1N1) virus were separated by a combination of ion-exchange chromatography and gel filtration. Seven different glycosylated tryptic peptide classes were obtained from the HA1 polypeptide, and only one glycosylated peptide was obtained from the HA2 polypeptide. Several of the tryptic fragments of HA1 and the HA2 glycopeptides were sulfated. The nature of the carbohydrate chain in each of the glycosylated tryptic peptides was determined from observations of the incorporation of different sugar precursors and susceptibility to cleavage by the enzyme endoglycosidase H and by compositional analysis by gas chromatography. Such analyses showed that three types of carbohydrate chains were present in HA1 (type I [complex], type II [high mannose], and hybrid type), whereas HA2 contained only type I oligosaccharide chains. The amino acid composition of each of the glycosylated tryptic peptides was also determined.

Structure of the carbohydrate chain of free secretory component from human milk.

Secretory component from human milk was found to contain 23.4% carbohydrate, which includes galactose, mannose, fucose, glucosamine, and sialic acid. Secretory component could be degraded by pronase or base-borohydride to yield the same, single type of carbohydrate chain. In the glycopeptide produced by pronase digestion, aspartic acid was the only amino acid present in molar quantities after amino acid analysis, which suggests that the carbohydrate moiety is linked to the polypeptide chain at asparagine residues. The positions of links between the various sugar units were studied by methylation analyses of: secretory component, periodate-oxidized and reduced secretory component, the fragment produced by base-borohydride treatment, and the pronase glycopeptide after treatment with specific glycosidases. Sugars released from the glycopeptide by various glycosidases were also quantitated. From the results of these studies a branched chain structure was assigned to the carbohydrate chain of secretory component.

Structural studies on the carbohydrate portion of fetuin.

The O-glycosidically linked carbohydrate chains of fetuin have been cleaved off by alkaline borohydride treatment and separated from the iV-glycosidically linked carbohydrate chains still bound to the protein. Both types of carbohydrate chains have been studied by sugar and methylation analysis before and after removal of Wacetylneuraminic acid (NeuNAc) residues. The iV-glycosidically linked carbohydrate chains have been further analyzed by Smith degradation, trifluoroacetolytic degradation, and degradation after chromium trioxide oxi- dation. As a result of these studies, the following structures for the carbohydrate chains of fetuin are proposed:

Further studies on the peptido-galactomannan from the yeast form of Cladosporium werneckii: Identification of O-acetyl substituents and isolation of the peptide components following β-elimination

The pathogenic yeast Cladosporium werneckii produces a surface peptido-phosphogalactomannan (PPGM) with a peptide backbone rich in serine and threonine to which three types of carbohydrate chains are linked. These chains are: Type a, glactomannan units linked through phosphodiester bonds to produce long chains of molecular weight about 50,000; type b more numerous short mannosyl oligosaccharide units, and type c, more infrequent, long galactomannan chains. The first two are linked to the peptide through alkali-labile bonds to serine and threonine of the peptide whereas type c chains are linked through alkali-stable bonds (Lloyd, K. O. (1972) Biochemistry, 11, 3884–3890). The PPGM sample can be separated into three or four major components by diethylaminoethyl (DEAE-) Sephadex chromatography. By means of sequential degradations with alkali and acid, the structural basis for this heterogeneity has been demonstrated. It is due to the presence of different proportions of the three types of chains in the various fractions. The presence of O-acetyl groups, mainly on the a chains, was demonstrated in PPGM by chemical analysis and by proton and 13C nuclear magnetic resonance spectroscopy. Purified a chains were isolated from PPGM following Pronase digestion. By taking advantage of the alkali lability of the carbohydrate-protein linkages it has been possible to cleave the peptide moiety away from the carbohydrate. By sequential chromatography on Bio-Gel P-100, Dowex 1 and Bio-Gel P-100, five modified peptide fractions were isolated. The molecular weights of these fractions varied from 9,500 to 18,500 as judged by polyacrylamide-gel electrophoresis. Unlike the original peptide, the modified peptides contained low amounts of serine and threonine. The predominant amino acids were alanine, glycine, aspartic acid and glutamic acid which together make up between 51 and 55% of the peptides. The high content of the last two amino acids accounts for the acidic nature of the peptides. It appears that each fraction consists of a slightly heterogeneous population of peptides very similar in amino acid composition. It is not clear whether the compositional and size heterogeneity exists in the original peptide or whether it arose during the isolation procedure.