Differential biosynthesis of polysialic acid on neural cell adhesion molecule (NCAM) and oligosaccharide accepters by three distinct alpha 2,8-sialyltransferases, ST8Sia IV (PST), ST8Sia II (STX), and ST8Sia III

Polysialylated neural cell adhesion molecule (NCAM) is thought to play a cr itical role in neural development. Polysialylation of NCAM was shown to be achieved by two alpha 2,8-polysialyltransferases, ST8Sia TV (PST) and ST8Si a II (STX), which are moderately related to another alpha 2,8-sialyltransfe rase, ST8Sia III. Here we describe that all three alpha 2,8-sialyltransfera ses can utilize oligosaccharides as accepters but differ in the efficiency of adding polysialic acid on NCAM. First, we found that ST8Sia III can form polysialic acid on the enzyme itself (autopolysialylation) but not on NCAM . These discoveries prompted us to determine if ST8Sia IV and ST8Sia II sha re the property of ST8Sia III in utilizing low molecular weight oligosaccha rides as accepters. By using a newly established method, we found that ST8S ia IV, ST8Sia II, and ST8Sia III all add oligosialic and polysialic acid on various sialylated N-acetyllactosaminyl oligosaccharides, including NCAM N -glycans, fetuin N-glycans, synthetic sialylated N-acetyllactosamines, and on a,alpha(2)-HS-glycoprotein, Our results also showed that monosialyl and disialyl N-acetyllactosamines can serve equally as an acceptor, suggesting that no initial addition of alpha 2,8-sialic acid is necessary for the acti on of polysialyltransferases. Polysialylation of NCAM by ST8Sia IV and ST8S ia II is much more efficient than polysialylation of N-glycans isolated fro m NCAM. Moreover, ST8Sia. IV and ST8Sia II catalyze polysialylation of NCAM much more efficiently than ST8Sia III. These results suggest that no speci fic acceptor recognition is involved in polysialylation of low molecular we ight sialylated oligosaccharides, whereas the enzymes exhibit pronounced ac ceptor specificities if glycoproteins are used as accepters.