Glycosaminoglycans (formerly known as muccopolysaccharides) are disaccharides consisting of two hexose derivatives in a repeating, un-branched chain. The hexose derivatives are most commonly glucosamine or galactosamine. Along with being a hexose derivative, either a carboxylate or sulfate group is attached to one or both monomers of the disaccharide, giving it a negative charge. Some of the most important glycosaminoglycans include chondroitin sulfate, dermatan sulfate, keratan sulfate, heparin, heparan sulfate, and hyaluronate.
Glycosaminoglycans are essential molecules in the body. They can covalently connect to proteins in order to form proteoglycans. Proteoglycans act more as carbohydrates than proteins as most of their molecular weight is due to glycosaminoglycans (95%). These proteoglycans are integral parts of connective tissue such as tendons and cartilage, they can act as anticoagulants, and they are also a component of the fluid that lubricates joints.
Glycosaminoglycans are regulated in the lysosome of the cell by being broken down in stages using specific enzymes. When those enzymes are not present in the lysosome, the undigested fragments build up in the cell, leading to what is referred to as a lysosomal storage disease. The class of lysosomal storage diseases involving glycosaminoglycans is called muccopolysaccharidosis (MPS). The types of MPS range from type 1-10 depending on the enzyme that is not present. This class of diseases can be debilitating and result mental retardation and loss of muscle function.
Biochemistry. 5th edition.Berg JM, Tymoczko JL, Stryer L.New York: W H Freeman; 2002