Oglykosylaatio

Oglykosylaatio, or O-glycosylation, is the covalent attachment of sugar molecules to hydroxyl groups of serine or threonine residues in proteins, producing glycoproteins and related glycoconjugates. In eukaryotes, O-glycosylation occurs in two major forms with distinct pathways and cellular locations: secretory mucin-type O-glycosylation and intracellular O-GlcNAcylation.

Mucin-type O-glycosylation begins in the Golgi apparatus when a family of polypeptide N-acetylgalactosamine transferases (ppGalNAc-Ts) transfers N-acetylgalactosamine (GalNAc) to Ser or Thr, generating O-GalNAc. This initial modification can be extended by a series of glycosyltransferases to form Core structures, such as Core 1 (Galβ1-3GalNAc) and Core 2 branches, leading to diverse O-glycan chains that are especially abundant on mucins and secreted glycoproteins. The resulting glycans influence protein stability, folding, and cell–cell interactions and play important roles in mucosal barriers and immune recognition.

O-GlcNAcylation is a separate, dynamic process that attaches N-acetylglucosamine (GlcNAc) to serine or threonine residues on intracellular and nuclear proteins. This modification is catalyzed by O-GlcNAc transferase (OGT) and removed by O-GlcNAcase (OGA). O-GlcNAcylation integrates with signaling pathways, transcription, and metabolism and often reciprocally interacts with phosphorylation.

Detection and study of Oglykosylaatio rely on specialized lectins, mass spectrometry, and specific enzymatic tools. Altered O-glycosylation patterns are associated with physiological states and diseases, notably cancer and congenital glycosylation disorders.