Molecular cloning and characterization of a novel human galactose 3-O-sulfotransferase that transfers sulfate to Galβ1→3GalNAc residue in O-glycans

We have identified a novel galactose 3-O-sulfotransferase, termed Gal3ST-4, by analysis of an expression sequence tag using the amino acid sequence of human cerebroside 3 ' -sulfotransferase (Gal3ST-1), The isolated cDNA contains a single open reading frame coding for a protein of 486 amino acids with a type II transmembrane topology. The amino acid sequence of Gal3ST-4 revealed 33%, 39%, and 30% identity to human Gal3ST-1, Gal beta1 -->3/ 4GlcNAc -->3 ' -sulfotransferase (Gal3ST-2) and Gal beta1 --> 4GlcNAc -->3 ' -sulfotransferase (Gal3ST-3), respectively. The Gal3ST-4 gene comprised at least four exons and was located on human chromosome 7q22, Expression of Gal3ST-4 in COS-7 cells produced a sulfotransferase activity that catalyzes the transfer of [S-35]sulfate to the C-3 ' position of Gal beta1 --> 3GalNAc alpha1-O-Bn. Gal3ST-4 recognizes Gal beta1 --> 3GalNAc and Gal beta1 -->3 (GlcNAc beta1 -->6)GalNAc as good substrates, but not Gal beta1 --> 3GalNAc(OH) or Gal beta1 -->3/4GlcNAc. Asialofetuin is also a good substrate, and the sulfation was found exclusively in O-linked glycans that consist of the Gal beta1 --> 3GalNAc moiety, suggesting that the enzyme is specific for O-linked glycans, Northern blot analysis revealed that 2.5-kilobase mRNA for the enzyme is expressed extensively in various tissues. These results suggest that Gal3ST-4 is the fourth member of a Gal:-->3-sulfotransferase family and that the four members, Gal3ST-1, GalST-2, Gal3ST-3, and Gal3ST-4, are responsible for sulfation of different acceptor substrates.