ST3Gal-II (SAT-IV)

Abstract

ST3Gal-II is a $β$-galactoside $α$2-3-sialyltransferase which is expressed in brain, liver, and striated muscle, and is presumed to be mainly involved in the synthesis of GD1a and GT1b. The cDNA sequences included an open reading frame coding for 350 amino acids, and the primary structure of this enzyme suggested a type II membrane protein topology with a putative domain structure consisting of four regions, as in other glycosyltransferases. ST3Gal-II exhibits characteristic motifs for the sialyltransferases called sialylmotifs L, S, and VS. ST3Gal-II also has a Kurosawa motif, as seen in the ST3Gal family and two members of the ST6GalNAc family (Tsuji 1999). The deduced amino acid sequence of ST3Gal-II (mouse) showed 76% identity in the active domain with that of ST3Gal-I (Lee et al. 1993, 1994). Northern blotting indicated that it is prominent in brain, liver, skeletal muscle, and heart. This enzyme expressed in COS- 7 cells exhibited transferase activity only toward the disaccharide moiety of Gal-$β$- 1,3-GalNAc of glycolipids, as well as glycoproteins and oligosaccharides such as ST3Gal-I, but asialo-GM1 and GM1 were much more suitable substrates for ST3Gal- II than for ST3Gal-L