• ST8SIA2 is characterized by the ability to synthesize polysialic acid (polySia) structures and can therefore be sub-classified as a polysialyltransferase. Sia polymers can have upto 400 Sia units.
• ST8SIA2 transfers Sia residue from CMP-Sia to Siaα2,3Gal- and Siaα2,6Gal/GalNAc on N-linked and/or O-linked glycans.
• Its function is similar to another polySia enzyme ST8Sia-4, though both proteins are expressed in different spatiotemporal patterns.
• Restricted activity has been shown mostly to brain proteins especially NCAM and SynCAM-1 in the IgG domain, though it can also act on other proteins with lower activity. Thus, there is a protein dependence for enzyme activity.
• PolySia imparts an anti-adhesive effect due to the bulky, polyanionic structure.
• It is implicated in psychiatric disorders and cancer.
• Endo-N-acylneuraminidase (Endo-N) specifically cleaves α2,8-linked polySia.
• ST8Sia-2 plus -4 DKO mice show severe phenotypes, such as postnatal growth retardation, precocious death, a high incidence of hydrocephalus, and agenesis or hypoplasia of major brain fiber tracts.
• While poly-Sia is not common to normal tissue, a number of cancers express polySia including neuroblastomas, Wilms tumors, medulloblastomas, pheochromocytomas, medullary thyroid carcinomas, non-small-cell lung carcinomas (NSCL), pituitary adenomas and breast cancer.