glycoconjugates

Glycoconjugates are biomolecules in which carbohydrates are covalently linked to proteins or lipids. They form a diverse class that includes glycoproteins, proteoglycans, glycolipids, and related structures such as lipopolysaccharides in bacteria. The carbohydrate moieties often mediate interactions at the cell surface, influence protein folding, and contribute to the structure of extracellular matrices.

Glycoproteins are proteins bearing oligosaccharide chains attached by N-glycosidic bonds to asparagine or by O-glycosidic bonds to serine or threonine. N-linked glycosylation begins in the endoplasmic reticulum and is further processed in the Golgi apparatus. Proteoglycans consist of a core protein with one or more glycosaminoglycan chains, such as heparan sulfate or chondroitin sulfate, attached to specific serine residues. These molecules are major components of the extracellular matrix and cell surfaces. Glycolipids consist of carbohydrate chains attached to lipid backbones, typically ceramide, and play roles in membrane organization and cell recognition. In bacteria, lipopolysaccharides are glycoconjugates that include lipid A, a core polysaccharide, and an O-antigen, and they contribute to the outer membrane’s properties and immune interactions.

Biosynthesis of glycoconjugates involves specialized enzymes called glycosyltransferases that assemble and modify carbohydrate chains in the endoplasmic reticulum and Golgi apparatus, with further remodeling by trimming and substitution. GPI-anchored proteins attach to membranes via glycosylphosphatidylinositol anchors.

Glycoconjugates participate in cell–cell and cell–matrix adhesion, signaling, immune recognition, and development. Altered glycosylation patterns are associated with diseases such as congenital glycosylation disorders and cancer, making glycoconjugates a focus of diagnostic and therapeutic research.