The proteoglycans are a group of macromolecules characterized by the covalent attachment of one or more sulfated glycosaminoglycan (GAG) chains to a protein core, and are an important constituent of the extracellular matrix. Cartilage contains a number of proteoglycans, the most abundant of which is aggrecan. This proteoglycan is characterized by its association with hyaluronic acid and link protein to form large macromolecular aggregates within the tissue. The large negative charge associated with the sulfated GAGs of these aggregates serves to draw water molecules into the tissue, thus giving cartilage its ability to resist compression under load (1 ).
