Sialyltransferase 7C (SIAT7C)

ST6GALNAC3 belongs to a family of sialyltransferases that transfer sialic acids from CMP-sialic acid to terminal positions of carbohydrate groups in glycoproteins and glycolipids. The unconjugated NeuAc-alpha-2,3-Gal-beta-1,3-GalNAc residue found in fetuin and GM1b was a poor substrate. The incorporated sialic acids contained an alpha-2,6 linkage, confirming that the enzyme belongs to the ST6GalNAc family. The truncated St6GalNAc III isoform showed very low enzymatic activity.GM1b was a good acceptor substrate for human ST6GalNAc III. No other gangliosides were significant acceptors. ST6GalNAc III also used sialyl-lactotetraosyl-ceramide and fetuin as acceptor substrates. Digestion of the sialylated fetuin product with glycopeptidase indicated that ST6GalNAc III sialylated O-glycans but not N-glycans.