noun, plural: proteoglycans
Proteoglycans are macromolecules of high molecular weight and are present in the body, especially in the connective tissues. They are a complex of protein and polysaccharide, characteristic of structural tissues of vertebrates, such as bone and cartilage, but also present on cell surfaces. Glycosaminoglycans (GAGs), the polysaccharide units in proteoglycans, are polymers of acidic disaccharides containing derivatives of the amino sugars glucosamine or galactosamine. The ribosomes synthesize the protein component of a proteoglycan. The protein is next moved into the lumen of the rER and then into the Golgi apparatus where it undergoes glycosylation. When it is in its final form, it is exported in secretory vesicles and into the extracellular matrix of the tissue.
Proteoglycans are a component of the extracellular matrix of animals. They fill the spaces between cells, forming complexes with other compounds such as collagen, hyaluronan, and other proteoglycans. They are also important in determining viscoelastic properties of joints and other structures subject to mechanical deformation.
Examples of proteoglycans are versican (a large chondroitin sulfate proteoglycan), perlecan, neurocan, aggrecan, brevican, fibromodulin, and lumican.