Eukaryotic cells synthesize many different kinds of glycoconjugates including glycoproteins, glycolipids and proteoglycans. Different cell compartments are equipped with specific synthetic enzymes that are used to build and modify the glycans. Once synthesized, the glycoconjugates reside in different cell locations or are secreted out of the cell.
In the lumen of the endoplasmic reticulum (ER)
N-Glycans are transferred to specific asparagine residues of the nascent polypeptide, a process intimately associated with protein folding (1). As the protein migrates through the ER and Golgi apparatus, specific enzymes trim back the glycan chain, while other enzymes add new monosaccharides to the glycan structure (2). Once in the Golgi the glycoproteins are sorted for distribution to their final destination: to specific cell compartments (such as the vacuole), to the cell surface, or to the extracellular space for secretion (3), as seen in the figure below.
A schematic diagram representing the synthesis of N -glycans in a eukaryotic cell. A pre-assembled glycan is transferred from a lipid carrier (Dol-p-p) to a nascent protein. The glycan is trimmed and then extended in the Golgi. Glycosyltransferases use activated sugars (nucleotide-sugars) as donors for the extension reactions. References
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