glikoprotein

Glikoprotein, more commonly known as glycoprotein, is a protein that contains covalently attached carbohydrate chains called glycans. The attached glycans vary in size and composition, leading to extensive microheterogeneity that can influence folding, stability, trafficking, and interactions. Glycoproteins are widespread, occurring in secreted enzymes and hormones, receptors, antibodies, and many cell-surface and extracellular matrix components.

Most glycoproteins acquire their glycans through two major types of linkages: N-linked glycosylation, where a glycan attaches to the nitrogen atom of an asparagine residue within a specific sequence, and O-linked glycosylation, where glycans attach to serine or threonine residues. Glycosylation begins in the endoplasmic reticulum with the assembly of a lipid-linked oligosaccharide, followed by transfer to the nascent protein and extensive processing in the Golgi apparatus. This maturation produces a range of N-glycans (high-mannose, hybrid, complex) and various O-glycan structures.

Glycoproteins perform diverse functions. They mediate cell–cell recognition and adhesion, influence immune responses (for example, glycosylation of antibodies affects Fc receptor interactions), participate in hormonal signaling, and contribute to the stability and activity of enzymes. On viral envelopes, glycoproteins facilitate host-cell entry. Mucins, a highly glycosylated class, protect and lubricate mucosal surfaces.

Clinical and biotechnological relevance is substantial. Abnormal glycosylation is linked to congenital disorders of glycosylation and to altered cancer glycosignatures that can serve as biomarkers. For therapeutic proteins, precise control of glycosylation is important for efficacy and pharmacokinetics, and glycoengineering is used to tailor glycan structures.