Mucopolysaccharide

Glycosaminoglycans (GAGs, formerly mucopolysaccharides) are linear polysaccharides of repeating disaccharide (two-sugar) units, consisting of one uronic sugar and one amino sugar. They are an evolutionarily ancient component of the extracellular matrix and connective tissues in the kingdom Animalia, with the most basal group featuring true GAGs being the genus Hydra. Due to their strong negative charge making them highly hydrophilic, they are abundant in body plan elements providing lubrication or cushioning, such as mucous membranes or cartilage. They are not found in plants, but exist in more limited contexts in bacteria, with similar backbone structures to animal GAGs but without the typical core proteins and located only on the inner surface of cytoplasmic membranes, suggesting a likely separate evolutionary origin. In the metabolic disorders known as mucopolysaccharidoses, abnormal accumulations of glycosaminoglycans occur due to enzyme deficiencies.