ER Quality Control Compartment (ERQC)

Stable Identifier
Homo sapiens
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Proteins that are released from the CNX or CRT complex with folding defects accumulate in a compartment of the ER called ERQC (Kamhi-Nesher et al. 2001). Here, the enzymes UGGG1 or UGGG2 are able to recognize glycoproteins with minor folding process and re-add the glucose on the alpha,1,3 branch; this is a signal for the transport of these glycoproteins back to the ER, where they can interact again with CNX or CRT in order to achieve a correct folding. At the same time that the glycoprotein is in the ERQC, the enzyme ER mannosidase I progressively removes the mannoses at positions 1A, 2A, B, C on N-glycans; when the mannose on 1A is trimmed, UDP-Glc:glycoprotein glucosyltransferases 1 and 2 (UGGT1 and 2) are no longer able to re-add the glucose, and therefore the protein is destined for ERAD. Glycoproteins subject to endoplasmic reticulum-associated degradation (ERAD) undergo reglucosylation, deglucosylation, and mannose trimming to yield Man6GlcNAc2 and Man5GlcNAc2. These structures lack the mannose residue that is the acceptor of glucose transferred by UGGT1 and 2. For years it has been thought that the removal of the mannose in position B of the N-glycan was the signal to direct proteins to degradation. However, this mechanism has been described better by Avezov et al (Avezov et al. 2008) and it has been demonstrated that even glycoproteins with Man8 or Man7 glycans can be re-glucosylated and interact again with CNX or CRT (for a review on this topic, see Lederkremer 2009 and Maattanen P et al, 2010).
Literature References
PubMed ID Title Journal Year
19616933 Glycoprotein folding, quality control and ER-associated degradation

Lederkremer, GZ

Curr Opin Struct Biol 2009
20347046 Protein quality control in the ER: the recognition of misfolded proteins

Thomas, DY, Bergeron, JJ, Gehring, K, Määttänen, P

Semin Cell Dev Biol 2010
18003979 Endoplasmic reticulum (ER) mannosidase I is compartmentalized and required for N-glycan trimming to Man5-6GlcNAc2 in glycoprotein ER-associated degradation

Herscovics, A, Ehrlich, M, Lederkremer, GZ, Avezov, E, Frenkel, Z

Mol Biol Cell 2008
11408579 A novel quality control compartment derived from the endoplasmic reticulum

Fromm, SV, Ehrlich, R, Lederkremer, GZ, Shenkman, M, Kamhi-Nesher, S, Tolchinsky, S

Mol Biol Cell 2001
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Orthologous Events
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