Beyond lectins: the calnexin/calreticulin chaperone system of the endoplasmic reticulum.
Calnexin and calreticulin are related proteins that comprise an ER chaperone system that ensures the proper folding and quality control of newly synthesized glycoproteins. The specificity for glycoproteins is conferred by a lectin site that recognizes an early oligosaccharide processing intermediate on the folding glycoprotein, Glc1Man9GlcNAc2. In addition, calnexin and calreticulin possess binding sites for ATP, Ca2+, non-native polypeptides and ERp57, an enzyme that catalyzes disulfide bond formation, reduction and isomerization. Recent studies have revealed the locations of some of these ligand-binding sites and have provided insights into how they contribute to overall chaperone function. In particular, the once controversial non-native-polypeptide-binding site has now been shown to function both in vitro and in cells. Furthermore, there is clear evidence that ERp57 participates in glycoprotein biogenesis either alone or in tandem with calnexin and calreticulin.
Department of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8. david.williams@utoronto.ca
David B
DB
Williams
D000818:Animals; D001665:Binding Sites; D037281:Calnexin / Q000737:chemistry / Q000378:metabolism*; D037282:Calreticulin / Q000737:chemistry / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002240:Carbohydrate Sequence; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D037102:Lectins / Q000378:metabolism; D018832:Molecular Chaperones; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding
D037282:Calreticulin; D006023:Glycoproteins; D037102:Lectins; D018832:Molecular Chaperones; D037281:Calnexin