Carbohydrates Glycosaminoglycans

Fig. 6.5. A proteoglycan molecule contains a protein core to which numerous carbohydrate (glycosaminoglycan) groups attach. Proteoglycan units can aggregate along a central hyaluronic acid backbone.

FIGURE 9.31 The known proteoglycans include a variety of structures. The carbohydrate groups of proteoglycans are predominantly glycosaminoglycans O-linked to serine residues. Proteoglycans include both soluble proteins and integral transmembrane proteins. 

Heparin is a carbohydrate-based (glycosaminoglycan) anticoagulant associated with many tissues, but mainly found stored intracellularly as granules in mast cells that line the endothelium of blood vessels. Upon release into the bloodstream, heparin binds to and thereby activates an additional plasma protein, namely antithrombin. The heparin-antithrombin complex then binds a number of activated clotting factors (including Ha, IXa, Xa, XIa and Xlla), thereby inactivating them. The heparin now disassociates from the complex and combines with another antithrombin molecule, thereby initiating another turn of this inhibitory cycle. 

Glucose for complex carbohydrate formation (e.g. glycans, glycoproteins, glycosaminoglycans. Appendix 6.2). 

Proteolytic digestion of proteoglycans liberates the carbohydrate side-chains, which are known as glycosaminoglycans (also known as mucopolysaccharides). All the glycosaminogly-cans contain derivatives of glucosamine or galactosamine. Six major groups are known, one of which is heparin. 

Wessel HP, Chucholowski A, Fingerle J, Iberg N, Marki HP, Muller R, Pech M, Pfister-Downar M, Rouge M, Schmid G, Tschopp T (1996) From glycosaminoglycans to heparinoid mimetics with antiproliferative activity. In Chapleur Y (ed) Carbohydrate mimics concepts and methods. Verlag Chemie, Weinheim, in press... 

The structures of the carbohydrate chains of the various glycosaminoglycans have been described in considerable detail,289 291a and therefore only a few limited aspects concerned with these glycoproteins will be discussed. 

The Main Structural Features of the Carbohydrate Chains of Glycosaminoglycans... 

Kariya, Y., Watabe, S., Kyogashima, M., Ishihara, M., and Ishii, T. (1997). Structure of fucose branches in the glycosaminoglycan from the body wall of the sea cucumber Stichopus japonicas. Carbohydr. Res. 297, 273-279. 

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