A serine-linked peptide of chondroitin sulfate

Fell-Muir Lecture: Proteoglycans and more--from molecules to biology

In this article the organization and functional details of the extracellular matrix, with particular focus on cartilage, are described. All tissues contain a set of molecules that are arranged to contribute structural elements. Examples are fibril-forming collagens forming major fibrillar networks in most tissues. The assembly process is regulated by a number of proteins (thrombospondins, LRR-proteins, matrilins and other collagens) that can bind to the collagen molecule and in many cases remain bound to the formed fibre providing additional stability and enhancing networking to other structural networks. One such network is formed by collagen VI molecules assembled to beaded filaments in the matrix catalysed by interactions with small proteoglycans of the LRR-family, which remain bound to the filament providing for interactions via a linker of a matrilin to other matrix constituents like collagen fibres and the large proteoglycans, e.g. aggrecan in cartilage. Aggrecan is contributing an extreme anionic charge density to the extracellular matrix, which by osmotic effects leads to water retention and strive to swelling, resisted by the tensile properties of the collagen fibres. Aggrecan is bound via one end to hyaluronan, including such molecules retained at the cell surface, to form very large molecular entities that interact with other constituents of the matrix, e.g. fibulins that can form their own network. Other important interactions are those with cell surface receptors such as integrins, heparan sulphfate proteoglycans, hyaluronan receptors and others. Many of the molecules with an ability to interact with these receptors can also bind to molecules in the matrix and provide a bridge from the matrix to the cell and induce various responses. In pathology, there is an imbalance in matrix turnover with often excessive proteolytic breakdown. This results in the formation of protein fragments, where cleavage provides information on the active enzyme. Those fragments released can be specifically detected employing antibodies specific to the cleavage site and used to diagnose and monitor e.g. joint disease at early stages.

Effects of glycosylation on fragments of tumour associated human epithelial mucin MUC1

The glycodecapeptide AcPAPGS(alpha GalNAc)T(alpha GalNAc)APPA and the C-terminal glycohexapeptide AcS(alpha GalNAc)T(alpha GalNAc)APPA have been synthesized by applying the N-terminal Fmoc group in combination with the heptyl ester cleavable by lipase-catalyzed hydrolysis at pH 7. The solution conformation of these MUC1-related synthetic glycopeptides and the control, non-glycosylated decapeptide AcPAPGSTAPPA have been investigated using NMR spectroscopy. The structural studies indicate that the glycohexapeptide has a folded structure in solution. For this molecule, unrestrained molecular dynamics has been used to confirm the presence of the observed solution through-space connections. The results indicate that the non-globular nature of MUC1 is due to both protein core sequence and the effect of carbohydrate.

Structural concepts of the human blood group A, B, H, Le(a), Le(b), I and i active glycoproteins purified from human ovarian cyst fluid

Regardless of the A, B, H, Le(a), Le(b), I and i activity, purified water-soluble blood group glycoproteins from human ovarian cyst fluid have a similar overall structure. They are polydisperse macromolecules (Mr 2.0 x 10(5) to several million) of similar composition (75 to 85% carbohydrate, 15 to 20% protein) and consist of multiple heterosaccharide side chains attached by an O-glycosidic linkage at their internal reducing ends to serine or threonine of the polypeptide backbone. About 90% of these carbohydrate side chains range in size from one to less than twenty-four sugar residues (twelve sugars in the internal structure and twelve key sugars specific as blood group determinants). Three-fourths of these side chains contain fewer than twelve sugars. A generalized blood group active carbohydrate chain is shown above. Three disaccharide units-Type I chain (Gal beta 1----3GlcNAc beta 1----3), Type II chain (Gal beta 1----4GlcNAc beta 1----6) and T determinant [Gal beta 1----3GalNAc alpha 1----Ser(Thr)]-are used to elucidate the internal structure of the carbohydrate chains. The complete internal structure is considered to have a core structure with four branches, to which the blood group key sugars are attached at the appropriate locations. The core structure is a tetrasaccharide, composed of one unit of Type I chain at the nonreducing end and the T determinant at the other end, linked to Ser or Thr of the protein moiety. Branch I is Type I chain and Branch II is Type II chain. They are linked to Gal at the nonreducing end of the core structure. Branch III is usually a Type II chain, but may sometimes be a Type I chain, linked to the GalNAc of the reducing end. The length of Branch III can be increased by adding one or more monosaccharides of Type I chain sequence such as Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4GlcNAc beta 1----6GalNAc alpha 1----Ser(Thr), a combination of Type I and Type II chains. A new Branch IV is made up of Type II chain, which in turn is linked to the Gal end of the T determinant. The Type II chains react with the antibody to the type XIV pneumococcal capsular polysaccharide and with the anti-I(Ma) cold agglutinin.(ABSTRACT TRUNCATED AT 400 WORDS)

Histochemical application of mild alkaline hydrolysis for selective elimination of O-glycosidically linked glycoproteins

A new technique to eliminate O-glycosidically linked glycoprotein (mucin-type glycoprotein) selectively has been developed. Composite paraffin sections were collodionized before and after alkaline treatment with 0.5 M NaOH in 70% ethanol; the effect of this procedure on mucosubstances was examined using the periodic acid-Schiff reaction. Exposure to alkaline hydrolysis for 72 to 144 hours at 4 C led to a complete loss of periodic acid-Schiff reactivity of epithelial mucins in rat sublingual gland, stomach and small intestine, but that of fuzzy coat, thyroid colloid, collagen fibers and tracheal cartilage was well preserved. These results agreed fairly well with biochemical findings. The present study also revealed that materials prepared by freeze-substitution provided the most satisfactory results.

Glycosaminoglycans of some mouse mastocytomas

The glycosaminoglycan fractions of four murine mastocytomas (AB-CBF1-MCT-1, AB-CXBG-MCT-1, AB-CXBI-MCT-1, and Furth), were isolated and characterized using microelectrophoresis, degradation with specific mucopolysaccharidases, paper chromatography and, in some instances, ion-exchange chromatography. Intramuscular and ascites tumors and tumors cultured in vitro were used. The glycosaminoglycans were labeled with [35S]sulfate and , in a few instances, with D-[6-3H]glucosamine. The glycosaminoglycan fraction obtained from the AB-CBF1-MCT-1 mastocytoma cultured in vitro consisted predominantly of dermatan sulfate-like material. On the other hand, the major components of the glycosaminoglycan fractions of the AB-CXBG-MCT-1 and AB-CXBI-MCT-1 and Furth tumors were observed to behave like heparin or heparan sulfate. In most of the mastocytoma samples examined, chondroitin 4-sulfate-like components were found to be present in smaller amounts, even in samples derived from tumor cells cultured in vitro. A component exhibiting a keratan sulfate-like behavior was detected in fractions obtained from the solid CXBG, CXBI and Furth tumors.

Proteoglycans of soluble fraction of mouse mastocytoma

Proteoglycans have been isolated from a high speed supernatant fraction of a mouse mastocytoma by procedures which should minimize alteration of the native protein-polysaccharide molecule. The methods used include in vivo labeling proteoglycans with 35S-sulfate, 3H-leucine and 3H-lysine, centrifugation of the tumor homogenate at 105,000 g, cetylpyridinium fractionation of the supernatant, and further purification of some of the fractions obtained by DEAE-cellulose column chromatography, gel filtration on Sepharose 4B and cellulose acetate electrophoresis. Two major sulfated proteoglycans were obtained, one containing keratan sulfate-like material (KSP-S), the other a heparin-like polymer (HP-S). The presence in HP-S of a compound similar to heparin was confirmed by its digestibility with flavobacterium heparinase. HP-S contained about 4 per cent protein. Glycine was the predominant amino acid, and serine did not appear to be involved in the peptide-carbohydrate linkage. The proteoglycan present in HP-S appeared to be homogeneous when examined using cellulose acetate electrophoresis. KSP-S was found to contain sialic acid and its protein content was significantly higher than that of HP-S. Glutamic and aspartic acids were the most abundant amino acids in KSP-S.

Chondroitin sulfate: inhibition of synthesis by puromycin

Puromycin reversibly inhibits synthesis of chondroitin sulfate by vertebral chondrocytes from 10-day-old chick embryos. Treatment of these cells with puromycin for 5 hours does not affect viability or capacity to multiply on subsequent release from their matrix. It is suggested that synthesis of this polysaccharide is coupled with that of protein; there may be a feedback control in its synthesis.