glicoproteinek

Glycoproteins are proteins with covalently attached carbohydrate chains, or glycans. The glycans are typically linked to the polypeptide via N-glycosidic bonds on asparagine residues or O-glycosidic bonds on serine or threonine residues, though other linkages occur. Glycosylation occurs mainly in the endoplasmic reticulum and Golgi apparatus and influences folding, stability, solubility, and trafficking.

Biosynthesis and diversity: N-linked glycosylation begins in the ER with assembly of a dolichol-linked oligosaccharide and its transfer to a nascent polypeptide; subsequent trimming and remodeling in the ER and Golgi generate diverse glycans. O-linked glycosylation adds sugars in the Golgi without a universal consensus sequence. The resulting glycoproteins vary by tissue and species.

Functions and examples: Glycoproteins play roles in cell-cell recognition, immune response, hormone activity, enzyme function, and structural components of mucins and the extracellular matrix. Notable examples include immunoglobulin G, transferrin, mucins, and many receptors such as selectins and integrins. Glycosylation modulates folding, stability, receptor binding, serum half-life, and antigenicity.

Clinical and analytical relevance: Altered glycosylation is associated with congenital disorders of glycosylation, cancer, and inflammatory diseases. Glycoprotein analysis uses mass spectrometry and lectin-based assays; biotechnology production of therapeutic glycoproteins emphasizes controlled glycosylation to ensure efficacy and safety.