Functional Diversity of Mammalian Sialyltransferases

Sialic acids are negatively charged acidic sugars. Sialyltransferases are enzymes that catalyze the synthesis of sialylglycoconjugates, which play important roles in various biological processes. Twenty members of the mammalian sialyltransferase superfamily have been identified to date. These enzymes are grouped into 4 families according to the type of carbohydrate linkage they synthesize: beta-galactoside alpha 2,3-sialyltransferases (ST3Gal-I-VI), beta-galactoside alpha 2,6-sialyltransferases (ST6Gal-I and -II), GalNAc alpha 2,6-sialyltransferases (ST6GalNAc-I-VI), and alpha 2,8-sialyltransferases (ST8Sia-I-VI). Each sialyltransferase has its specific function in the complicated mammalian body system. In this review, we describe the functional diversity of mammalian sialyltransferases on the basis of recent studies and discuss the necessity for 20 different sialyltransferases.