Congenital disorders of glycosylation

Abstract

Numerous proteins are glycosylated with monosaccharides and/or oligosaccharide structures (Fig. 42.1), also termed glycans, attached to the polypeptide chain. Most extracellular proteins, such as serum proteins (transferrin, clotting factors), most membrane proteins and several intracellular proteins (such as lysosomal enzymes), are glycoproteins. The glycans are defined by their linkage to the protein: N-glycans are linked to the amide group of asparagine, and O-glycans are linked to the hydroxyl group of serine or threonine. Synthesis of Nglycans, schematically represented in Fig. 42.1, proceeds in three stages: formation of nucleotide-linked sugars, assembly, and processing.