Molecular cloning and expression of an N-acetylgalactosamine-4-O-sulfotransferase that transfers sulfate to terminal and non-terminal beta 1,4-linkedN-acetylgalactosamine

We have identified and characterized an N-acetyl-galaetosamine-4-O-sulfotra nsferase designated GalNAc-4-ST2 (GenBank(TM) accession number AF332472) ba sed on its homology to HNK-1 sulfotransferase (HNK-1 ST). The cDNA predicts an open reading frame encoding a type II membrane protein of 443 amino aci ds with a 12-amino acid cytoplasmic domain, a 23-amino acid transmembrane d omain, and a 408-amino acid luminal domain containing four potential N-link ed glycosylation sites. GalNAc-4-ST2 displays a high degree of amino acid s equence identity with GalNAc-4-ST1 (46%), HNK-1 ST (23%), chondroitin 4-O-s ulfotransferase-1 (C4ST-1) (27%), and chondroitin 4-O-sulfotransferase-2 (C 4ST-2) (24%), GalNAc-4-ST2 transfers sulfate to the C-4 hydroxyl of termina l beta1,4-linked GalNAc in the sequence GalNAc beta1,4GlcNAc beta -R found on N-linked oligosaccharides and nonterminal beta1,4-linked GalNAc in chond roitin and dermatan. The translated region of GalNAc-4-ST2 is encoded by fi ve exons located on human chromosome 18q11.2, Northern blot analysis reveal s a 2.1-kilobase transcript. GalNAc-4-ST2 message is most highly expressed in trachea and to a lesser extent in heart, liver, pancreas, salivary gland , and testis. The I.M.A.G.E. cDNA clone 49547 contains a putative GalNAc-4- ST2 splice form with an open reading frame encoding a protein of 358 amino acids that lacks the transmembrane domain and the stem region. This form of GalNAc-4-ST2 is not retained by transfected cells and is active against ch ondroitin but not terminal beta1,4-linked GalNAc. Thus, as with GalNAc-4-ST 1, sequences N-terminal to the catalytic domain contribute to the specifici ty of GalNAc-4-ST2 toward terminal beta1,4-linked GalNAc.