COORDINATE AND RESTRICTED EXPRESSION OF THE PROXAAARG LYS-SPECIFIC GALNAC-TRANSFERASE AND THE TA-1,4GLCNAC-BETA-1,2MAN-ALPHA-4-SULFOTRANSFERASE/

Asn-linked oligosaccharides terminating with the sequence SO4-4GalNAcb eta1,4GlcNAcbeta1,2Manalpha (S4GGnM) are present on the glycoprotein h ormones lutropin and thyrotropin, pro-opiomelanocortin, and tissue fac tor pathway inhibitor. The peptide motif ProXaaArg/Lys (PXR/K), which is recognized by a PXR/K-specific GalNAc-transferase, is present in ea ch of these glycoproteins 6-9 residues NH2-terminal to an Asn glycosyl ation site. Both the PXR/K-specific GalNAc-transferase and a GalNAcbet a1,4GlcNAcbeta1,2Manalpha (GGnM)-4-sulfotransferase are required for s ynthesis of the S4GGnM sequence. Glycoproteins which do not contain th e PXR/K motif but bear Asn-linked oligosaccharides terminating with GG nM or sialic acidalpha2,3/6GGnM have also been described, suggesting a distinct GalNAc-transferase may be responsible for their synthesis. W e have examined a number of tissues and cultured cell lines for the tr ansfer of sulfate to the trisaccharide acceptor GGnM and transfer of G alNAc to oligosaccharide acceptors on protein which do, human chorioni c gonadotropin (hCG), and do not, transferrin (Trf), contain the PXR/K motif. The PXR/K-specific GalNAc-transferase and the GGnM-4-sulfotran sferase are expressed in salivary gland, pituitary, lacrimal gland, ki dney, and brain, and in the cell lines AtT-20, 293, SHSY5Y, and alphaT 3. In contrast Bowes, EL-4, and B16L6 cell extracts transferred GalNAc to oligosaccharides acceptors on Trf but not on hCG. A number of tiss ues and cell lines displayed transfer of GalNAc to both hCG and to Trf suggesting that two distinct GalNAc-transferases were present. The GG nM-4-sulfotransferase was expressed in tissues and cell lines which ex pressed the PXR/K-specific GalNAc-transferase but not in cell lines ex pressing exclusively the Trf-specific GalNAc-transferase. Thus, the PX R/K-specific GalNAc-transferase and the GGnM-4-sulfotransferase are co ordinately expressed in a number of tissues other than pituitary. The Trf-specific GalNAc-transferase may account for the presence of beta1, 4-linked GalNAc on glycoproteins which do not contain the PXR/K motif.