This review summarizes retro-translocation across the ER membrane to the cytosol, for example, as it occurs in ERAD.īrodsky, J. Retro-translocation of proteins from the endoplasmic reticulum into the cytosol. Protein degradation in the endoplasmic reticulum. Protein glucosylation and its role in protein folding. Role of N-linked oligosaccharide recognition, glucose trimming, and calnexin in glycoprotein folding and quality control. The ubiquitin–proteasome proteolytic pathway: destruction for the sake of construction. Quality control mechanisms during translation. Posttranslational quality control: folding, refolding, and degrading proteins. Protein oligomerization in the endoplasmic reticulum. Translational accuracy and the fitness of bacteria. Peptides from degraded proteins are presented on the cell-surface and thereby ensure the early detection of, for example, viral infections. Protein folding and maturation are intrinsically error-prone processes, and a substantial fraction of proteins are degraded rapidly after synthesis. Here, export and retention signals, the effects of protein mobility in the ER and selective inclusion in ER exit sites are crucial factors. This system depends crucially on the direct interaction of the two lectin chaperones, calnexin and calreticulin, with newly synthesized glycoproteins.Īt the level of ER export, protein sorting at ER exit sites determines whether a protein can leave the ER. The protein-specific level ('secondary QC') involves the recognition of individual proteins or protein families by specialized chaperones.Īn important factor for determining ER retention is protein stability - the lower the overall stability of a protein the more likely it is to be retained.įor glycoproteins, there is a QC system that is based on the recognition of specific glycosylation intermediates of N-linked glycans. The general level ('primary QC') applies to all proteins and involves the recognition of structural and biophysical features that are common to non-native proteins. The QC system works at two levels - general and protein-specific. These proteins are key players in the quality-control (QC) system, which regulates the transport of proteins from the ER to other compartments of the secretory pathway. Protein folding in the endoplasmic reticulum (ER) is assisted by several molecular chaperones and folding factors.
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