N-Glycans

N-glycans are covalently attached to certain Asn residues in glycoproteins during translation and translocation into the endoplasmic reticulum, and subsequently modified during glycoprotein transit through the secretory pathway. The most common consensus sequence for attachment of an N-glycan is Asn-X (not Pro)-Ser/Thr. Although necessary, this consensus is not sufficient for N-glycan addition to occur. N-glycans have many different functions that may be independent of the glycoprotein to which they are attached, or may specifically affect its production and functions. The factors that govern optimal N-glycan attachment and maturation are encoded by ~300 genes. Mutations in these genes lead to Congenital Disorders of Glycosylation (CDG), rare diseases arising from mutations in genes involved in protein glycosylation.