ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00290.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Ten years ago, we anticipated future results by building the Y‐shaped molecular model of a biantennary glycan. Progressively, this structure has been refined and modified thanks to experimental data obtained by using physical methods: X‐ray diffraction, electron spin resonance (EPR), nuclear magnetic resonance (NMR) including two‐dimensional NMR and one‐dimensional 1H‐nuclear Overhauser effect (NOE) experiments, neutron scattering and hard‐sphere exo‐anomeric (HSEA) calculations. So, the concept evolved successively from the Y‐, to the T‐, the bird‐ and the “broken wing”‐conformation, until the demonstration, that these conformers are interconvertible. The bird‐conformation as well as the concept of the mobility of antennae are in a good agreement with the reactivity of lectins, including membrane lectins, by rendering accessible any specific sugar structure, and with the activity of glycosyltransferases by making reachable the substitutable hydroxyl groups even in the case of pentaantennary structures. Along this line, we know now that the tetraantennary glycans adopt an “umbrella conformation” in which the four antennae are disposed parallely to the protein surface and act as protective shields. So could be explained the resistance towards proteases and the weak antigenicity of numerous glycoproteins as well as the peculiar behaviour and resistance of metastatic cancerous cells since it has been recently demonstrated that membrane glycoproteins and fibronectin of this kind of cells are significantly enriched in

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00291.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

This laboratory has developed schemes for the control of biosynthesis of N‐ and O‐glycosyl oligosaccharides based on studies in cell‐free systems of glycosyl‐transferase substrate specificities. These schemes are based on assumptions that may not be universally correct. For example, we have ignored the possible compartmentation of reactions in different cells or in different organelles within a cell. Recent evidence has indicated that the Golgi apparatus has at least three functionally distinct regions (cis, medial and trans). The addition of galactosyl and sialyl residues to the antennae of complex and hybrid N‐glycans probably occurs entirely within the trans‐cisternae while the N‐acetylglucosaminyl‐transferases which initiate these antennae appear to be located in a denser region of the Golgi (cis and/or medial cisternae). We have constructed a modified scheme for the biosynthesis of the antennae of N‐glycans. This scheme combines our substrate specificity data (H. Schachter, S. Narasimhan, P. Gleeson and G. Vella, 1983, Can. J. Biochem. Cell Biol., 61, 1049‐1066) with compartmentation data. It provides a basis for understanding the control of glycoprotein synthesis in normal tissues and in certain lectin‐resist

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The distribution of cell surface negatively‐charged macromolecules was determined electron microscopically on untreated and on retinoic acid (RA)‐treated cultured human osteosarcoma Hs791 and chondrosarcoma Hs705 cells using cationized ferritin (CF), an electron‐dense marker of anionic sites. Labeling on the surface of prefixed cells was continuous and uniform whether they were grown in the absence or presence of RA. In contrast, CF distribution on unfixed cells was markedly affected by RA; CF labeling of untreated cells occurred in patches and clusters whereas the label on RA‐treated cells was continuous, as on prefixed cells. CF labeling of unfixed cells decreased considerably after incubation of the cells either with hyaluronidase or neuraminidase. There was also a reduction in patching and clustering. Changes induced by RA in the apparent membrane microviscosity, in neuraminidase‐releasable sialic acid, or in transglutaminase activity could not be related to the effect of RA on CF‐induced anionic site redistribution since these characteristics were modulated differently in the two cell lines. In contrast, RA increased the sialylation of specific cell surface membrane glycoproteins on both cell types. These results suggest that RA prevents redistribution of cell surface sialoglycoconjugates and glycosaminoglycans by CF. This effect may be the result of increased sialylation of specific surface components and may be related causally to the suppression of the transformed phenotype in the sa

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

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 glycop

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Soluble lectins of chicken, rat, frog, and the cellular slime mold, Dictyostelium discoideum, were purified and specific antibodies raised against these proteins were used to immunohistochemically localize the lectins in and around the tissues in which they were synthesized. Within cells, some of these soluble lectins (chicken‐lactose‐lectin‐II in intestinal goblet cells, discoidin II in prespore cells) appear to be concentrated within vesicles whereas others (e.g., rat beta‐galactoside lectin in pulmonary alveolar and smooth muscle cells) appear to be free in the cytoplasm. All of these lectins are eventually secreted to extracellular sites in developing or adult tissues. The sites include mucin (chicken‐lactose‐lectin‐II in intestine); developing extracellular matrix (chicken‐lactose‐lectin‐I in muscle; Xenopus laevis lectin in blastula stage embryos); slime (discoidin I); developing spore coat (discoidin II); and a specialized extracellular matrix, elastic fibers (rat beta‐galactoside lectin in lung). In cases where this has been studied in detail (discoidin I, discoidin II, and chicken‐lactose‐lectin‐II), the lectin is associated with a complementary extracellular ligand, at least transiently. Lectin‐ligand interactions presumably confer specialized properties in these par

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00295.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Rat hepatocytes in primary culture bind, internalize and eventually degrade asialoglycoproteins. This process is mediated by a specific receptor in the hepatocyte plasma membrane. The endocytic pathway by which ligand molecules are translocated to lysosomes has been examined by the development of biological assays capable of distinguishing ligand populations at various points in the process. Inhibitors have been identified that perturb particular transitions that define the endocytic pathway. In the present paper, inhibition by the bacterial tripeptide leupeptin is compared to the effect of colchine plus cytochalasin B. The latter combination impedes intracellular segregation of ligand and receptor while leupeptin inhibits intralysosomal proteolysis. However, evidence is presented to indicate that the inhibitory effects colchine plus cytochaasin B consists of at least two components. One component is independent of the presence of ligand whereas the other is observed only when ligand is present together with the drugs.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00296.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The low pH dependent membrane fusion reaction responsible for the delivery of the Semliki Forest virus genome into the host cell for replication was visualized by electron microscopy. In order to increase the frequency at which fusion images could be detected a reversible inhibitor, ammonium chloride, was used to synchronize endosomal acidification, and 20 degrees C incubation was employed to concentrate virus particles into the endosomal compartment.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00297.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The presence and the sugar specificity of membrane lectins on the cell surface of mouse L1210 leukemia cells were demonstrated by using various neoglycoproteins (glycosylated serum albumin) substituted with fluorescein or methotrexate. Neoglycoproteins were prepared by reaction of glycosidophenylisothiocyanates with bovine serum albumin. The binding of neoglycoproteins to L1210 cells depends on the nature of the carried sugar and on the number of bound sugar residues per neoglycoprotein molecule. The best results were obtained with fucosylated serum albumin containing 25 +/‐ 5 residues of fucose. The amount of cell‐associated fluorescein‐labeled neoglycoproteins was several fold higher at 37 degrees C than at 4 degrees C suggesting a specific endocytotic process. The membrane lectin‐mediated endocytosis was further demonstrated by showing that the cell‐associated fluorescence upon cell incubation in the presence of fluorescein‐labeled neoglycoproteins at 37 degrees C increased several fold after addition of monensin, a proton/sodium ionophore known to raise the pH of endosomes and lysosomes. The analysis of fluorescein‐labeled neoglycoproteins association to the L1210 cells were achieved by quantitative flow cytofluorometry after standardization with calibrated polystyrene sulfonate beads carrying various amounts of 1‐(fluoresceinylthioureido)‐4,8‐diazalicosane. In addition, the cytotoxicity of neoglycoprotein‐bound methotrexate was shown to be related to the presence and to the nature of the carried sugar: fucosylated serum albumin was shown to be the most efficient neoglycoprotein carrier, and to have a cytotoxicity close to that of anti L1210 cell IgM monoclonal antibody

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00298.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Several lectin‐like activities were detected on the surface of unfixed, viable BHK cells by reaction with FITC‐labelled glycosylated albumin derivatives. A prominent surface staining was obtained with the beta‐lactosyl, beta‐N‐acetylgalactosaminyl, alpha‐mannosyl and beta‐N‐acetylglucosaminyl derivatives. Endogenous lectin‐like activities were also detected in BHK cell homogenates by haemagglutination of glutaraldehyde‐fixed rabbit erythrocytes. Haemagglutinating activity was purified by chromatography of sodium deoxycholate‐extracts of BHK cell microsomal fractions on Sepharose 4B and asialofetuin‐Sepharose 4B. A purified agglutinin was eluted from the latter column with 0.2 M thiodigalactoside. The haemagglutination mediated by the purified factor was inhibited by thiodigalactoside, N‐acetylgalactosamine, galactosyl‐beta 1‐4‐N‐acetylglucosamine and several glycoproteins. The purified agglutinin agglutinated trypsinised, fixed normal BHK cells more readily than several ricin‐resistant cell lines. By contrast, a mannose‐binding lectin from rabbit serum reacted equally well with normal and mutant cells. These results are in general agreement with models of cell‐cell adhesion involving the interaction of surface located lectins with carbohydrate sequences o

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00299.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY