Molecular Cloning and Characterization of a Novel Human Galactose 3-O-Sulfotransferase That Transfers Sulfate to Galβ1→3GalNAc Residue in O-Glycans

Abstract

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 beta 1-->3/4GlcNAc:-->3'-sulfotransferase (Gal3ST-2) and Gal beta 1-->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 [(35)S]sulfate to the C-3' position of Gal beta 1-->3GalNAc alpha 1-O-Bn. Gal3ST-4 recognizes Gal beta 1-->3GalNAc and Gal beta 1-->3(GlcNAc beta 1-->6)GalNAc as good substrates, but not Gal beta 1-->3GalNAc(OH) or Gal beta 1-->3/4GlcNAc. Asialofetuin is also a good substrate, and the sulfation was found exclusively in O-linked glycans that consist of the Gal beta 1-->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, Gal3ST-2, Gal3ST-3, and Gal3ST-4, are responsible for sulfation of different acceptor substrates.