The glycosaminoglycans (GAGs) are linear polysaccharides made up of a disaccharide repeat unit, in which one of the monosaccharides is a hexosamine and the other is either a hexose (in keratan sulfate only) or an uronic acid. Most GAGs exist as the O-linked glycan part of protein glycoconjugates known as proteoglycans and carry sulfate substituents, making them the most acidic class of biological macromolecules. The exception is the GAG hyaluronan (HA), which is not attached to a protein core and is not sulfated.
GAGs are structural components in the extracellular matrix throughout the animal kingdom. Some glycosaminoglycans, through specific interactions with small extracellular proteins, are essential for embryonic development and play roles in the response of the organism to infection and injury. Hyaluronan has a very high molecular weight, and its rheological properties are important to its role in the extracellular...