Enzymatic activity of a developmentally regulated member of the sialyltransferase family (STX): evidence for α2,8‐sialyltransferase activity toward N‐linked oligosaccharides

We have detected sialyltransferase activity of recombinant mouse STX, which was cloned from rat brain as a new member of the sialyltransferase family, but sialyltransferase activity of which had not been detected previously [Livingston and Paulson, J. Biol. Chem. (1993) 268, 11504–11507]. The activity of mouse STX was specific toward sialylated glycoproteins. N‐Glycanase treatment and linkage‐specific sialidase treatment of glycoproteins revealed that STX transfers sialic acids through α2,8‐linkages to only N‐linked oligosaccharides of glycoproteins. However, polymerase activity for polysialic acid synthesis was not detected for this sialyltransferase. Since this α2,8‐sialyltransferase gene is highly restricted in fetal and newborn brain, it may be involved in the polysialylation of glycoproteins, especially of N‐CAM.