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#quality control

2 public questions tagged with this topic.

Protein Sorting and Trafficking

The main function of the calnexin/calreticulin cycle is to:

Calnexin and calreticulin together with oxidoreductase ERp57 and glucosyltransferase UGGT constitute specialized folding cycle dedicated to N-glycosylated proteins comprising more than eighty percent of secretory proteome. After glucose trimming to monoglucosylated form by glucosidase I and II, nascent proteins bind lectin site of membrane-bound calnexin or soluble calreticulin, which prevents aggregation, retains them in ER lumen and recruits ERp57 via extended proline-rich P-domain arm to catalyze disulfide bond formation and isomerization. Folding sensor UGGT inspects surface hydrophobicity

Ref: Caramelo & Parodi, J Biol Chem 283: 2008, Calnexin-Calreticulin Cycle in Folding.

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Protein Sorting and Trafficking

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.

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