Extracellular Matrix/Growth Factor Interactions

Growth factors bind to extracellular matrices and onto cell surfaces, and this binding is mainly mediated by proteoglycans. Proteoglycans are proteins that carry an unusual carbohydrate, a glycosaminoglycan. The glycosaminoglycans are large carbohydrates that are composed of repeating disaccharide units and exist in four main forms: heparan sulfate and heparin, chondroitin sulfate and dermatan sulfate, keratan sulfate, and hyaluronic acid. The first three are protein-bound glycosaminoglycans in their natural form, and they all contain sulfate; hyaluronic acid is made as a free glycosaminoglycan and lacks sulfate (see Ruoslahti 1989; Kolset and Gallagher 1990). The glycosaminoglycan substitution depends on the ability of the protein to serve as an acceptor for xylosyltransferase, the enzyme that begins the synthesis of most types of glycosaminoglycans.