Transport of free and N-linked oligomannoside species across the rough endoplasmic reticulum membranes

The N-glycosylation process occurs in the rough endoplasmic reticulum. It requires the transport of glycosyl donors into the lumen and the exit of the glycosylated products toward the secretory pathway. Besides this main flow, the formation of free oligomannosides, glycopeptides, and misfolded glycoproteins which do not enter the secretory pathway and are cleared out of the endoplasmic reticulum by specific transports has been demonstrated. This review focuses on the export mechanisms of these three side products of the N-glycosylation process and discusses their physiological significance.