glikozaminoglikan

Glycosaminoglycans, known in Polish as glikozaminoglikany, are a family of long, unbranched polysaccharides that are highly negatively charged owing to sulfate and carboxyl groups. They consist of repeating disaccharide units and occur largely in the extracellular matrix (ECM) and on cell surfaces. The main classes are hyaluronic acid, and the sulfated GAGs heparan sulfate, heparin, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Each disaccharide unit typically contains a hexosamine (N-acetylglucosamine or N-acetylgalactosamine) linked to a uronic acid (D-glucuronic or L-iduronic acid). Sulfation patterns and the presence of iduronic acid influence physical properties and interactions with proteins.

GAGs most commonly exist as part of proteoglycans, where one or more GAG chains are covalently attached to a core protein. Hyaluronic acid is unique in not being covalently attached to a protein and can form intact networks by interacting with proteoglycans. Biosynthesis occurs in the Golgi apparatus for most GAGs, with hyaluronic acid synthesized at the plasma membrane by hyaluronan synthases. Degradation occurs in lysosomes or extracellularly via specific enzymes.

Functionally, GAGs contribute to tissue hydration and turgor, provide a hydrated gel that cushions joints, and modulate cell signaling by binding growth factors and cytokines. Clinically, heparin is used as an anticoagulant; hyaluronic acid is employed in ophthalmology, wound healing, and cosmetic fillers; chondroitin sulfate is used in supplements. Defects in GAG degradation lead to mucopolysaccharidoses, a group of lysosomal storage disorders.