Characterization of a thyroid sulfotransferase responsible for the 3-O-sulfation of terminal beta-D-galactosyl residues in N-linked carbohydrate units.
Calf thyroid microsomes were found to contain an enzyme which catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phospho[35S]sulfate (PAPS) to C-3 of terminal galactose residues in beta 1----4 linkage to GlcNAc. This sulfotransferase is believed to be involved in the biosynthesis of the recently described Gal(3-SO4) capping groups present in the N-linked oligosaccharides of thyroglobulin (Spiro, R.G., and Bhoyroo, V. D. (1988) J. Biol. Chem. 263, 14351-14358). Assays with various native and modified glycopeptides indicated that the enzyme acted optimally on complex-type carbohydrate units in which beta-linked Gal has been uncovered by desulfation or brought into a terminal position by removal of sialyl and/or alpha-galactosyl residues. With fetuin asialoglycopeptides as acceptors (Km = 0.1 mM) the transfer of sulfate from PAPS (Km = 6.3 microM) had a pH optimum of approximately 7.0, required Mn2+ ions (10-50 mM) and was markedly stimulated by Triton X-100 (0.1%) and ATP (2 mM). The same enzyme apparently sulfated free N-acetyllactosamine (LacNAc; Km = 0.69 mM) and its ethyl glycoside, indicating that it had no absolute requirement for a peptide recognition site. Studies with a number of disaccharides related to LacNAc provided information relating to the specifying role of the beta 1----4 galactosyl linkage and the configuration at C-2 of the sugar to which it is attached. Hydrazine-nitrous acid-NaBH4 treatment of the 35S-labeled products from sulfotransferase action on asialoglycopeptides as well as on the ethyl glycoside of LacNAc yielded the same disaccharide, Gal(3-SO4) beta 1----4 anhydromannitol, as is obtained from a similar treatment of thyroglobulin. Subcellular distribution studies indicated that the PAPS:galactose 3-O-sulfotransferase is located in the Golgi compartment which is consistent with the late occurrence of the requisite beta-galactosylation step. It is proposed that in certain tissues the ultimate nature of the capping groups attached to glycoproteins containing terminal Gal beta 1----4GlcNAc sequences could be the result of a competition between this 3-O-sulfotransferase and sialyl- and/or alpha-galactosyltransferases.
Kato
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Department of Biological Chemistry, Harvard Medical School, Boston, Massachusetts 02215.
Spiro
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D000117:Acetylglucosamine / Q000378:metabolism; D000606:Amino Sugars / Q000378:metabolism; D000818:Animals; D001212:Asialoglycoproteins / Q000378:metabolism; D001667:Binding, Competitive; D002236:Carbohydrate Conformation; D050260:Carbohydrate Metabolism; D002417:Cattle; D004187:Disaccharides / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology; D008970:Molecular Weight; D017830:Octoxynol; D010724:Phosphoadenosine Phosphosulfate / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D013379:Substrate Specificity; D013431:Sulfates / Q000378:metabolism*; D015238:Sulfotransferases / Q000378:metabolism*; D013961:Thyroid Gland / Q000201:enzymology* / Q000648:ultrastructure
D000606:Amino Sugars; D001212:Asialoglycoproteins; D004187:Disaccharides; D013431:Sulfates; D011092:Polyethylene Glycols; C000458:N-acetyllactosamine; D008345:Manganese; D010724:Phosphoadenosine Phosphosulfate; D017830:Octoxynol; D015238:Sulfotransferases; D000117:Acetylglucosamine; D005690:Galactose