The ER glycoprotein quality control system.
The endoplasmic reticulum (ER) is the major site for folding and sorting of newly synthesized secretory cargo proteins. One central regulator of this process is the quality control machinery, which retains and ultimately disposes of misfolded secretory proteins before they can exit the ER. The ER quality control process is highly effective and mutations in cargo molecules are linked to a variety of diseases. In mammalian cells, a large number of secretory proteins, whether membrane bound or soluble, are asparagine (N)-glycosylated. Recent attention has focused on a sugar transferase, UDP-Glucose: glycoprotein glucosyl transferase (UGGT), which is now recognized as a constituent of the ER quality control machinery. UGGT is capable of sensing the folding state of glycoproteins and attaches a single glucose residue to the Man9GlcNAc2 glycan of incompletely folded or misfolded glycoproteins. This enables misfolded glycoproteins to rebind calnexin and reenter productive folding cycles. Prolonging the time of glucose addition on misfolded glycoproteins ultimately results in either the proper folding of the glycoprotein or its presentation to an ER associated degradation machinery.
Dejgaard
Selma
S
Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montreal, Quebec, H3A 2B2, Canada.
Nicolay
Johan
J
Taheri
Maryam
M
Thomas
David Y
DY
Bergeron
John J M
JJ
D000595:Amino Acid Sequence; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D016415:Sequence Alignment
D006023:Glycoproteins; D005964:Glucosyltransferases