Calnexin (membrane protein) and calreticulin (soluble in ER) are two lectins (proteins that can bind a glycan) which recognize the mono-glucosylated form of the N-glycan and mediate the folding of the glycoproteins to which they are attached to (Ou WJ et al, 1993; Nauseef Wm et al, 1995). Calmegin is another chaperone with the same role expressed only in testis (van Lith M et al, 2007). These lectins act as chaperons, providing a protected environment where the unfolded glycoprotein can fold without forming interactions with other proteins or components in the ER. The unfolded protein can loop between these two steps multiple time, therefore this process is called the 'calnexin/calreticulin cycle'. If the protein achieves correct folding, it is modified by Mannosidase I and then moved to the cis-Golgi where the glycan is further processed.
Karala, AR, Gatehouse, JA, van Lith, M, Ruddock, LW, Saunders, PT, Bown, D, Benham, AM
Cameron, PH, Thomas, DY, Bergeron, JJ, Ou, WJ
Clark, RA, McCormick, SJ, Nauseef, WM
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