Molecular cloning and expression of the pituitary glycoprotein hormone N-acetylgalactosamine-4-O-sulfotransferase

N-Linked oligosaccharides terminating with the sequence SO4-4-GalNAcβ1,4GlcNAcβ1,2Manα are present on the pituitary hormones lutropin (LH), thyrotropin, and pro-opiomelanocortin. The sulfated structures on LH are essential for expression of its biologic function in vivo. We have cloned the N-acetylgalactosamine-4-sulfotransferase (GalNAc-4-ST1, GenBankTM accession number AF300612), which mediates sulfate addition to the N-linked oligosaccharides on LH and other pituitary glycoproteins with terminal (β1,4-linked GalNAc based on its homology to HNK-1 sulfotransferase (HNK-1 ST). GalNAc-4-ST1 displays 23% identity to HNK-1 ST and 28% to chondroitin 4-sulfotransferase 1 (C4ST-1) and 26% to chondroitin 4-sulfotransferase 2 (C4ST-2). The cDNA predicts a type II transmembrane protein of 424 amino acids with four potential N-linked glycosylation sites and a single membrane-spanning domain. GalNAc-4-ST1 has putative 5′-phosphosulfonate and 3′-phosphate binding sites. Three more carboxyl-terminal regions of unknown function also show a high degree of identity with HNK-1 ST, C4ST-1, and C4ST-2. The membrane-bound form of GalNAc-4-ST1 transfers sulfate to GalNAcβ1,4GlcNAcβ-R but not to chondroitin, whereas truncated forms of GalNAc-4-ST1 that are released into the medium transfer sulfate to both GalNAcβ1,4GlcNAcβ-R and chondroitin. The first 118 amino acids of GalNAc-4-ST1 appear to contribute to both its activity and specificity for terminal β1,4-linked GalNAc. GalNAc-4-ST1 also efficiently transfers sulfate to N-linked oligosaccharides on native LH and other glycoproteins terminating with β1,4-linked GalNAc. A single transcript of 2.4 kilobases is most highly expressed in the pituitary and other regions of the central nervous system. The GalNAc-4-ST1 gene is located on human chromosome 19q13.1.