Structural and Functional Diversity of the Heparan Sulfate Proteoglycans

Several enzymes, cell adhesion molecules, growth factors, proteinase inhibitors and extracellular matrix components possess heparin-binding domains, and are profoundly affected in their reactivities with third parties in the presence of this glycosaminoglycan. Heparin, e.g. markedly accelerates the reaction of antithrombin III with thrombin1, and allows bFGF to interact with its receptor at the cell surface2,3. This implies that a whole series of biological processes may be modulated by the availability of heparin or heparin-like polysaccharides. Heparin is, however, not likely to be physiologically involved in most of these situations. Heparin is mainly a product of mast cells, which is stored intracellularly and is released upon degranulation of these cells at sites of inflammation. In contrast, the surfaces of most cells and the extracellular matrix are decorated by heparan sulfate, a glycosaminoglycan that shares several structural and functional features with heparin.