The Assembly and Transfer of Oligosaccharide Chains to Proteins
All eukaryotic cells are capable of the synthesis of glycoproteins that are destined to become components of the plasma membrane. In addition, many cell types commit a significant portion of their protein biosynthetic activity to the synthesis of secreted and/or lysosome-packaged glycoproteins.
The synthesis of membrane, secretory, or lysosomal glycoproteins is a highly segregated process that occurs within an intracellular membrane system composed of the endoplasmic reticulum, transfer vesicles, Golgi apparatus, and secretory vesicles. During their translation, glycosylation and processing the glycoproteins are completely isolated from the cytoplasm and travel to the cell surface (in the case of membrane glycoproteins), to the extracellular environment (in the case of secretory glycoproteins), or to the lysosomes (in the case of lysosomal enzymes) as part of, or within, these membrane compartments.
The assembly of N-linked oligosaccharide chains occurs in the endoplasmic reticulum and involves the stepwise preassembly of the oligosaccharide chain on dolichyl phosphate followed by en bloc transfer of the oligosaccharyl unit to the growing polypeptide chain.
Subsequent modifications to the oligosaccharide chains of N-linked glycoproteins are initiated in the rough endoplasmic reticulum and completed in the Golgi apparatus.
KeywordsRough Endoplasmic Reticulum Signal Recognition Particle Sugar Nucleotide Oligosaccharide Chain Cytoplasmic Face
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