Structure and metabolism of proteoglycans and glycosaminoglycans

Proteoglycans and glycosaminoglycans have the common structural characteristics of linear polysaccharide chains consisting of a hexosamine alternating with another sugar. They play an important role in skin as part of the support matrix of connective tissue, and may be related to cell-cell, and cell-matrix interactions. In general the polysaccharide chains are covalently linked to protein and may contain varying amounts of sulfate resulting in a strong negative charge. Biosynthesis consists of the formation of the protein core followed by the sequential addition of sugars and sulfate to the nonreducing ends of growing chains. The synthetic process is highly organized with the final polysaccharide polymerization and sulfation taking place in the Golgi. Degradation of the proteoglycans is less well understood but probably involves endoglycosidases, exoglycosidases, and proteases which work in concert to degrade these substances.