N-Glycosylation of secretory and membrane-bound proteins is an essential and highly conserved protein modification of eukaryotes. In the endoplasmic reticulum (ER), a combination of various enzymes, chaperones, lectins and cargo receptors constitutes the “glycoprotein quality control” (GQC) system, which elaborately regulates folding, transport and degradation of glycoproteins. Thus, function of asparagine linked sugar chains in the GQC process has been attracting attention. Understanding of these phenomena has progressed as a result of interaction analyses and substrate specificity studies of glycan related enzymes using synthetic sugar chains. In this review, our approach to the systematic synthesis of the ER type of asparagine linked sugar chains (N-glycans) and recent progress of this field is described.
