Glýkósýlunin

Glýkósýlunin is the enzymatic process by which carbohydrate groups, or glycans, are covalently attached to proteins or lipids, producing glycoproteins and glycolipids. The two major forms are N-linked glycosylation, where a glycan is attached to the amide nitrogen of asparagine within a specific sequence, and O-linked glycosylation, where glycans attach to the hydroxyl groups of serine or threonine residues.

N-linked glycosylation begins in the endoplasmic reticulum with the assembly of a dolichol-linked oligosaccharide that is transferred en bloc to the nascent polypeptide by the oligosaccharyltransferase complex. After transfer, the glycan is trimmed and remodeled as the protein advances through the ER and Golgi apparatus. O-linked glycosylation occurs predominantly in the Golgi, where individual sugars are added stepwise by glycosyltransferases.

Glycosylation influences protein folding, quality control, stability, solubility, trafficking, and interactions at the cell surface. It shapes cell–cell communication, immune recognition, and pathogen interactions, and glycan structures often vary by cell type, developmental stage, and physiological conditions. Altered glycosylation patterns are associated with various diseases and biological processes, including cancer and inflammatory responses.

Defects in glycosylation pathways can cause congenital disorders of glycosylation (CDG), highlighting the clinical importance of these modifications. Beyond basic biology, glycosylation is central to biotechnology, including the engineering of therapeutic proteins and vaccine design. Analytical methods such as mass spectrometry-based glycoproteomics and lectin-based assays are used to study glycosylation patterns.