Carbohydrate Structure Of Glycoproteins Research Articles

Glycosylation is involved in malignant properties of cancer cells

Cancer cells express unique carbohydrate structures in glycoproteins and glycolipids, and their structures have been considered to be cancer-associated antigens. However, the involvement of their antigens in the malignant properties has not been well understood. The functional studies of glycosyltransferase genes revealed important regulatory roles of glycosylation in the malignant properties of cancer cells. In particular, we have characterized the molecular signaling pathways that are activated or inactivated by gangliosides in various cancer cells. Our results indicated that disialyl gangliosides GD3 and GD2 enhance malignant properties of human melanoma, osteosarcoma, and small cell lung cancer cells. However, monosialyl ganglioside GM1 attenuates these properties in melanoma and lung cancer cells. In addition to glycolipids, glycoproteins are also reported to be involved in regulating malignant properties and maintenance of cancer stem cells.

Localization of plant N‐glycan processing enzymes along the secretory pathway

N‐glycosylation is an abundant covalent protein modification in all eukaryotic cells. The biosynthesis and processing of protein N‐linked glycans results from a series of highly co‐ordinated step‐by‐step enzymatic conversions occurring mainly in the endoplasmic reticulum (ER) and Golgi apparatus. N‐glycan processing enzymes are thought to act on cargo glycoproteins in a highly ordered fashion in an assembly line. Thus, the subcellular localization of these enzymes together with their in vivo substrate specificity determines the carbohydrate structures of glycoproteins transported through the secretory pathway. While the substrate specificities of many plant N‐glycan processing enzymes are fairly well characterized, the molecular mechanisms underlying enzyme localization to the ER and Golgi have remained largely elusive so far. This review discusses current data on ER and Golgi localization of plant N‐glycan processing enzymes.

Red blood cell antigens responsible for inherited types of polyagglutination.

The three described types on inheritable polyagglutination are related to altered carbohydrate structures in glycoproteins or/and glycolipds on the erythrocyte surface. HEMPAS, a condition causing anemia and other pathological symptoms, is characterized by impaired biosynthesis of N-glycans, mostly those carried by band 3 and band 4.5 erythrocyte membrane proteins. Cad erythrocytes have abnormal glycophorin O-glycans, structurally related to the more common human Sd(a) and murine CT determinants, and accumulate an Sd(a)-like ganglioside. NOR erythrocytes express recently detected abnormal alpha-galactose-terminated glycosphingolipids, which strongly react with G. simplicifolia IB4 isolectin, but do not react with human anti-Galalpha1-3Gal antibodies.

Incorporation of ammonium into intracellular UDP‐activated N‐acetylhexosamines and into carbohydrate structures in glycoproteins

Incorporation of ammonium into intracellular UDP‐activated N‐acetylhexosamines and into carbohydrate structures in glycoproteins

Incorporation of ammonium into intracellular UDP-activatedN-acetylhexosamines and into carbohydrate structures in glycoproteins

The negative effects of ammonia on animal cells, especially in vitro cultures, are well known, but the mechanism of how ammonia inhibits cell growth and influences the glycosylation of proteins is not completely understood. We investigated the ammonium action on the synthesis of the intracellular UDP-N-acetylhexos- amines (UDPGNAc), which are precursors of glycosylation as well as on N-linked oligosaccharides of a recombinant human IL-2 mutant variant model glycoprotein expressed in BHK-21 cells under defined and controlled culture conditions in a continuously perfused bioreactor. The examinations were based on our previous observations that increased ammonia concentrations in the medium lead to the intracellular formation and accumulation of UDPGNAc (Ryll et al., 1994). The kinetics of formation of the UDPGNAc pool after adding ammonia and its reconstitution to normal conditions are shown. To study the pathway leading to the intracellular increase of UDPGNAc, the uptake and incorporation of 15NH4+ was confirmed by the detection of 15N in UDP-N-acetylglucosamine (UDP-GlcNAc). UDP-GlcNAc was purified using high pH anion-exchange chromatography with pulsed amperometric detection and analyzed by GC/MS. The proportion of UDP-GlcNAc containing 15N was approximately 60% and corresponds quantitatively to the increased intracellular concentration of UDP-GlcNAc. In order to confirm the direct influence of ammonia on protein glycosylation, the human IL-2 mutant glycoprotein variant IL-Mu6, bearing a novel N-glycosylation site, has been produced under defined protein-free medium conditions in the presence of 15NH4Cl. IL-Mu6 glycoprotein was purified and N-glycans released were analyzed by matrix-assisted laser desorption ionization time of flight mass spectroscopy. Maximally 60-80% of N-acetylated sugars in N-glycan structures contained 15N indicating that ammonium is used as a building block during synthesis of the carbohydrate structures expressed from in vitro cultivated mammalian cells.

A Study on the Lectin Reactivity of Alpha-Fetoprotein Produced by Hepatoid Adenocarcinomas and Yolk Sac Tumors

The carbohydrate structure of glycoproteins is considered to be tissue-specific or cell type-specific, but there have been no reports on the differences of the carbohydrate structure of alpha-fetoproteins (AFPs) produced by histologically identical tumors in different tissues. The lectin affinity electrophoresis of hepatoid adenocarcinomas and yolk sac tumors from different organs suggested that either the tumor heterogeneity or the tissue specificity is possibly involved, the lectin reactivity of the AFP sugar chain structure produced by the tumors in different tissues.

Light and electron microscopic detection of lectin binding sites in normal and disordered human gastric tissues.

Lectins are now widely used as histochemical markers and probes for carbohydrate structures in glycoproteins. In the present study, a method is described for the light and electron microscopic detection of Ulex europaeus agglutinin I binding sites in the normal and neoplastic tissues. The results showed that the gastric mucus-producing cells and some vascular endothelial cells could be strongly stained with labelled lectin in normal mucous membrane. The positive staining reactivity was reduced greatly in neoplastic tissue either in paraffin sections or in thin sections. This suggested that the secretions of gastric carcinoma are different from those of normal gastric mucosa and represent differentiation of neoplastic cells to some degree.

Demonstration by monoclonal antibodies that carbohydrate structures of glycoproteins and glycolipids are onco-developmental antigens.

The hope that hybridoma antibodies would reveal unique cell surface antigens during embryogenesis, differentiation and oncogenesis has been replaced by the realization that such antigens are mainly carbohydrate structures of glycoproteins and glycolipids occurring in many cell types. These findings either may reflect limitations in the methods of selection of hybridoma antibodies or may point to important roles for the diverse carbohydrate structures as receptors for regulators of cell growth and differentiation.

Comparative studies of new marker lectins for alkali-labile and alkali-stable carbohydrate chains in glycoproteins

1. 1. Three new lectins, obtained from the Indian Jack fruit Artocarpus integrifolia, the Betelnut Areca catechu and the sponge Geodia were studied with respect to their haemagglutination pattern with various normal and enzyme-treated red cells and with special regard to their precipitin reactions with different glycosubstances. 2. 2. In comparative studies with a large number of neuraminidase-treated human serum glycoproteins and glycosubstances of other origins it was found, that the reaction of the Jack fruit lectin shows a striking similarity with the lectin from the mushroom Agaricus bisporus. 3. 3. Whereas these two lectins react with the alkali-labile chain of the Thomsen-Friedenreich (TF) Type (3-0-β- d-galactosyl-N-acetyl- d-galactosamine) in serum and other glycoproteins, in a similar, but not identical way as the anti-TF peanut lectin, the ones from Geodia and Betelnut combine in different ways with the alkali-stable carbohydrate structures in glycoproteins.