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.