Endoplasmic reticulum oligosaccharides

Lehrman MA Oligosaccharide-based information in endoplasmic reticulum quality control and other biological systems. J Biol Chem. 2001 276 8623. 

Many proteins on the surface of the plasma membrane, and the majority of secreted proteins, contain oligosaccharide residues that are post-translationally added to the endoplasmic reticulum and in the Golgi apparatus (see p.230). By contrast, cytoplasmic proteins are rarely glycosylated. Glycoproteins can contain more than 50% carbohydrate however, the proportion of protein is generally much greater. 

Helenius A (1994) How N-linked oligosaccharides affect glycoprotein folding in the endoplasmic reticulum. Mol Biol Cell 5 253-265 Hershko A (1997) Roles of ubiquitin-mediated proteolysis in cell cyde control. Curr Opin Cell Biol 9 788-99... 

Jakob CA, Burda P, Roth J, Aebi M (1998) Degradation of misfolded endoplasmic reticulum glycoproteins in Saccharomyces cerevisiae is determined by a specific oligosaccharide structure. J Cell Biol 142 1223-1233 Janson LW, Ragsdale K, Luby-Phelps K (1996) Mechanism and size cutoff for steric exclusion from actin-rich cytoplasmic domains. Biophys ) 71 1228-1234 Jeffers M, Taylor GA, Weidner KM, Omura S, Vande Woude GF (1997) Degradation of the Met tyrosine kinase receptor by the ubiquitin-proteasome pathway. Mol Cell Biol 17 799-808... 

D-Mannosylation of lipid-linked oligosaccharides and of proteins has been found to occur in rough, endoplasmic reticulum.188 192 In hen-... 

Further studies will be needed in order to resolve the intriguing question as to how the glycosyl groups of the activated sugars that are usually found in the cytoplasm are transferred to the growing chain of the lipid-bound oligosaccharide inside the lumen of the endoplasmic reticulum. 

During the transfer of the nascent peptide into the lumen of the cistern ae of the endoplasmic reticulum, the leader sequence is cleaved off. The glycoproteins remain anchored into the membrane by either their N- or carboxyl-terminus. The attachment of the oligosaccharide occurs concomitantly with the synthesis of the protein. As discussed in Section 11,2, this is a high-mannose structure that can be modified during transport on intracellular membranes, and then yields a complex type. 

Synthesis of the dolichol-linked oligosaccharide. The reaction starts on the cytosolic side of the endoplasmic reticulum. Seven single-step reactions lead to the heptasaccharide that is linked to dolichol... 

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