Which sugar residue is used as a quality control marker in N-linked glycosylation?
Quality control of N-glycosylated proteins exploits reversible presence of terminal glucose as molecular mark of folding status. Precursor Glc3Man9GlcNAc2 transferred en bloc to asparagine in Asn-X-Ser/Thr sequon by oligosaccharyltransferase carries three glucoses. Immediately after transfer, alpha-glucosidase I removes outer α1-2 glucose, alpha-glucosidase II heterodimer of catalytic α subunit and regulatory β subunit removes second α1-3 glucose producing monoglucosylated Glc1Man9GlcNAc2 that is high-affinity ligand for calnexin and calreticulin lectin chaperones retaining protein in ER for f
Ref: Helenius & Aebi, Annu Rev Biochem 73: 2004, Glucose Marker in N-Glycosylation Quality Control.
