Nglycosyl

Nglycosyl, more commonly called N-glycosylation, is a post-translational modification in which a preassembled oligosaccharide is covalently attached to the asparagine residue of a nascent protein. The attachment occurs at the sequon Asn-X-Ser/Thr, where X is any amino acid except proline. In eukaryotes this process predominantly takes place in the endoplasmic reticulum, with further processing in the Golgi apparatus.

The transfer of the oligosaccharide is catalyzed by the oligosaccharyltransferase (OST) complex. In higher eukaryotes the oligosaccharide is initially assembled on a lipid carrier called dolichol and then transferred en bloc to the polypeptide as it emerges into the ER lumen. After transfer, the glycoprotein undergoes trimming and remodeling by ER- and Golgi-resident enzymes, producing a spectrum of N-glycan types, including high-mannose, hybrid, and complex forms.

N-glycosylation plays several essential roles. It assists proper protein folding and quality control through interactions with chaperones such as calnexin and calreticulin, influences protein stability and trafficking, and modulates cell-cell recognition and receptor activity. The pattern and structure of N-glycans can affect protein localization, half-life, and interactions with other biomolecules.

Dysregulation or genetic defects in N-glycosylation can lead to congenital disorders of glycosylation, with a range of clinical manifestations from developmental delay to multi-organ dysfunction. N-glycosylation is also present in some bacteria and archaea, where distinct OST enzymes mediate organism-specific glycan transfers, illustrating its evolutionary diversity.