Proteome and\nGlycoproteome Analyses Reveal Regulation\nof Protein Glycosylation Site-Specific Occupancy and Lysosomal Hydrolase\nMaturation by <i>N</i>‑Glycan-Dependent ER-Quality\nControl

<i>N</i>-Glycan-dependent endoplasmic reticulum\nquality\ncontrol (ERQC) primarily mediates protein folding, which determines\nthe fate of the polypeptide. Monoglucose residues on <i>N</i>-glycans determine whether the nascent <i>N</i>-glycosylated\nproteins enter into and escape from the calnexin (CANX)/calreticulin\n(CALR) cycle, which is a central system of the ERQC. To reveal the\nimpact of ERQC on glycosylation and protein fate, we performed comprehensive\nquantitative proteomic and glycoproteomic analyses using cells defective\nin <i>N</i>-glycan-dependent ERQC. Deficiency of MOGS encoding\nthe ER α-glucosidase I, CANX, or/and CALR broadly affected protein\nexpression and glycosylation. Among the altered glycoproteins, the\noccupancy of oligomannosidic <i>N</i>-glycans was significantly\naffected. Besides the expected ER stress, proteins and glycoproteins\ninvolved in pathways for lysosome and viral infection are differentially\nchanged in those deficient cells. We demonstrated that lysosomal hydrolases\nwere not correctly modified with mannose-6-phosphates on the <i>N</i>-glycans and were directly secreted to the culture medium\nin <i>N</i>-glycan-dependent ERQC mutant cells. Overall,\nthe CANX/CALR cycle promotes the correct folding of glycosylated peptides\nand influences the transport of lysosomal hydrolases.