Sialobiology and the Polysialic Acid Glycotope Occurrence, Structure, Function, Synthesis, and Glycopathology

Polysialic acids (polySia)* are a structurally diverse family of linear carbohydrate chains that consist of N-acetylneuraminic acid (Neu5Ac) or N-glycolylneuraminic acid (Neu5Gc) residues, usually joined internally by α2,8-, α2,9-, or alternating α2,8-/α2,9-ketosidic linkages. 3-Deoxy-D-glycero-D-galacto-2- nonulosonic acid (KDN) is a unique deaminated form of Sia, and polyKDN chains share many properties in common with polySia (Table I). The finding of poly(Neu5Ac), poly(Neu5Gc), poly(Neu5Ac,Neu5Gc), poly(KDN) chains and their partially O-acetylated and O-lactylated forms in salmonid fish egg glycoproteins demonstrates the natural occurrence of multiple forms of these unique sugar chains.