Molecular cloning and characterization of GalNAc (4-sulfotransferase expressed in human pituitary gland

We have previously cloned chondroitin-4-sulfotransferase (C4ST) cDNA from m ouse brain. In this paper, we report cloning and characterization of GalNAc 4-sulfotransferase (GalNAc4ST), which transfers sulfate to position 4 of t he nonreducing terminal GalNAc residue. The obtained cDNA contains a single open reading frame that predicts a type II transmembrane protein composed of 424 amino acid residues. Identity of the amino acid sequence between Gal NAc4ST and human C4ST was 30%. When the cDNA was transfected in COS-7 cells , sulfotransferase activity toward carbonic anhydrase VI was overexpressed but no sulfotransferase activity toward chondroitin or desulfated dermatan sulfate was increased over the control. Sulfation of carbonic anhydrase VI by the recombinant GalNAc4ST occurred at position 4 of the GalNAc residue o f N-linked oligosaccharides. The recombinant GalNAc4ST transferred sulfate to position 4 of GalNAc residue of p-nitrophenyl GalNAc, indicating that th is sulfotransferase transfers sulfate to position 4 at the nonreducing term inal GalNAc residue. Dot blot analysis showed that the message of GalNAc4ST was expressed strongly in the human pituitary, suggesting that the cloned GalNAc4ST may be involved in the synthesis of the nonreducing terminal GalN Ac 4-sulfate residues found in the N-linked oligosaccharides of pituitary g lycoprotein hormones.