Molecular cloning and expression of a novel human beta-Gal-3-O-sulfotransferase that acts preferentially on N-acetyllactosamine in N- and O-glycans

A novel cDNA-encoding galactose 3-O-sulfotransferase was cloned by screenin g the expressed sequence tag data base using the previously cloned cDNA enc oding a galactosyl ceramide 3-O-sulfotransferase, which we term Gal3ST-1, T he newly isolated cDNA encodes a novel 3-O-sulfotransferase, termed Ga13ST- 3, that acts exclusively on N-acetyllactosamine present in N-glycans and co re2-branched O-glycans, These conclusions were confirmed by analyzing CD43 chimeric proteins in Chinese hamster ovary cells expressing corea beta1,6-N -acetylglucosaminyl-transferase. The acceptor specificity of Ga13ST-3 contr asts with that of the recently cloned galactose 3-O-sulfotransferase (Honke , It, Tsuda, M, Koyota, S,, Wada, P,, Iida-Tanaka N., Ishizuka, I., Nakayam a, J,, and Taniguchi, N. (2001) J, Biol Chem 276, 267-274), which we term G a13ST-2 in the present study because the latter enzyme can also act on core 1 O-glycan and type 1 oligosaccharides, Gal beta1 --> 3GlcNAc. Moreover, Ga 13ST-3 but not Ga13ST-2 can act on Gal beta1 -->4(sulfo -->6)GlcNAc, indica ting that disulfated sulfo --> 3Gal beta1 -->4(sulfo -->6) GlcNAc -->R may be formed by Gal3ST-3 in combination with GlcNAc 6-O-sulfotransferase. Alth ough both Ga13ST-2 and Ga13ST-3 do not act on galactosyl ceramide, Ga13ST-3 is only moderately more homologous to Ga13ST-2 (40.1%) than to Gal3ST-1 (3 8.0%) at the amino acid level, Northern blot analysis demonstrated that tra nscripts for Ga13ST-3 are predominantly expressed in the brain, kidney, and thyroid where the presence of 3 ' -sulfation of N-acetyllactosamine has be en reported. These results indicate that the newly cloned Ga13ST-3 plays a critical role in 3 ' -sulfation of N-acetyllactosamine in both O- and N-gly cans.