Transfer of N-glycan to the protein

Stable Identifier
Reaction [transition]
Homo sapiens
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The 14-sugar N-glycan precursor (aka lipid-linked oligosaccharide, LLO), synthesized in the previous reactions, is attached in a single step to a nascent protein, releasing the dolichyl phosphate anchor and the as-yet unfolded glycoprotein. The reaction occurs cotranslationally as the growing peptide chain leaves a ribosome associated with the ER membrane and enters the ER lumen. This reaction is catalyzed by the oligosaccharyltransferase (OST) complex, comprising at least seven proteins; DAD1 (Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit DAD1), DDOST (OST48 in yeast), RPN1 (ribophorin 1), RPN2 (ribophorin 2), OST4, TUSC3 (N33), MAGT1 (magnesium transporter protein 1) and either STT3A or STT3B (Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3A and B), which contain the catalytic domain (Kelleher & Gilmore 2006). A mutation in RPN2 is associated with CDG-Ix (Vleugels et al. 2009). The signal for glycosylation is the consensus sequence Asn - X - Thr/Ser, where the first amino acid is always Asn, the second can be any amino acid except for Pro, and the third position may be Thr, Ser or Cys, with a preference for the first (Breuer et al. 2001). Not all Asn - X - Thr/Ser sites are modified in vivo (Petrescu et al. 2004).
Literature References
PubMed ID Title Journal Year
11470266 Oligosaccharyltransferase is highly specific for the hydroxy amino acid in Asn-Xaa-Thr/Ser

Hardt, B, Bause, E, Bartoschek, A, Breuer, W, Klein, RA

FEBS Lett 2001
19835842 Screening for OST deficiencies in unsolved CDG-I patients

Foulquier, F, Matthijs, G, Schollen, E, Vleugels, W

Biochem Biophys Res Commun 2009
14514716 Statistical analysis of the protein environment of N-glycosylation sites: implications for occupancy, structure, and folding

Milac, AL, Petrescu, SM, Petrescu, AJ, Wormald, MR, Dwek, RA

Glycobiology 2004
16317064 An evolving view of the eukaryotic oligosaccharyltransferase

Kelleher, DJ, Gilmore, R

Glycobiology 2006
Catalyst Activity

dolichyl-diphosphooligosaccharide-protein glycotransferase activity of OST complex [endoplasmic reticulum membrane]

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