Proteoglycans consist of a protein core (brown) and one or more covalently attached glycosaminoglycan chains (dark blue, HS, heparan sulfate; yellow, CS/DS, chondroitin sulfate/dermatan sulfate; light blue, KS, keratan sulfate). Membrane proteoglycans either span the plasma membrane (type I membrane proteins) or are linked by a glycosylphosphatidylinositol (GPI) anchor. Extracellular matrix proteoglycans are usually secreted, but some proteoglycans can be proteolytically cleaved and shed from the cell surface (not shown).