Abstract
Differential expression of glycosyltransferases has the potential to generate functionally distinct glycoforms of otherwise identical proteins. We have previously demonstrated the presence of unique oligosaccharides terminating with GalNAc-4-SO4 on the pituitary glycoproteins lutropin (LH), thyroid stimulating hormone (TSH), and pro-opiomelanocortin (POMC). A glycoprotein hormone:GalNAc-transferase and a GalNAc-4-sulfotransferase are present in the pituitary and can account for the synthesis of these unique oligosaccharides on specific glycoproteins. Both transferases are coordinately expressed in a number of tissues in addition to pituitary, including submaxillary gland, lacrimal gland, and kidney, suggesting that additional glycoproteins bearing oligosaccharides terminating with GalNAc-4-SO4 are synthesized in these tissues. In this study we show that while the glycoprotein hormone:GalNAc-transferase and the GalNAc-4-sulfotransferase are coordinately expressed in bovine submaxillary gland, the GalNAc-transferase is expressed in the parotid gland in the absence of the GalNAc-4-sulfotransferase. The relative expression of these two transferases in submaxillary and parotid glands correlates with the presence of unique Asn-linked oligosaccharides on carbonic anhydrase VI (CA VI) synthesized in each of these tissues. The majority of Asn-linked oligosaccharides on CA VI synthesized in submaxillary gland terminate with GalNAc-4-SO4. In contrast, CA VI which is synthesized in bovine parotid gland bears oligosaccharides which terminate predominantly with beta 1,4-linked GalNAc which is not sulfated. The presence of different terminal residues on the Asn-linked oligosaccharides of submaxillary and parotid CA VI thus correlates with the complement of transferases in these glands and suggests differing biological roles for submaxillary and parotid CA VI.
Highlights
The abbreviations used are: LH, luteinizing hormone; TSH, thyroid stimulating hormone; POMC, proopiomelanocortin; tissue factor pathway inhibitor (TFPI), tissue factor synthesized in the anterior lobe of the pituitary and the placenta, respectively [1]
We report here that both the glycoprotein hormone:GaINActransferase and the GaINAc-4-sulfotransferase are expressed in bovine submaxillary gland and that the majority of Asnlinked oligosaccharides present on the secreted form of carbonic anhydrase (CA VI) synthesized by bovine submaxillary gland terminate with GaINAc-4-S04 In addition, we demonstrate that a similar proportion of Asn-linked oligosaccharides on carbonic anhydrase VI (CA VI) synthesized in the bovine parotid gland terminate with IH,4-linked GalNAc which is not sulfated
Relative Expression of Glycoprotein Hormone:GalNAc-transferase and GalNAc-4-sulfotransferase Differs in Bovine Submaxillary and Parotid Glands-We have previously shown that a GalNAc-transferase and GaINAc-4-sulfotransferase with the same specificity and properties as the glycoprotein hormone:GaINAc-transferase and GaINAc-4-sulfotransferase found in pituitary are expressed at high levels in a number of rat tissues, including the submaxillary gland, lacrimal gland, and kidney [22]
Summary
Vol 270, No 11, Issue of March 17, pp. 5985--5993, 1995 Printed in U.S.A. Differential Expression of GalNAc-4-sulfotransferase and GalNActransferase Results in Distinct Glycoforms of Carbonic Anhydrase VI in Parotid and Submaxillary Glands*. The relative expression of these two transferases in submaxillary and parotid glands correlates with the presence of unique Asn-linked oligosaccharides on carbonic anhydrase VI (CA VI) synthesized in each of these tissues. Glycoproteins expressed in cells which differ in their complement of glycosyltransferases will potentially bear oligosaccharides differing in structure, producing distinct glycoforms of otherwise identical proteins which may differ in their biologic functions. We demonstrated this to be the case for equine lutropin (LH) and chorionic gonadotropin (CG) which are. Equine LH and CG bear Asn-linked oligosaccharides terminating with 804-4-GalNAc{31,4GlcNAc{31,2Mana and sialic acid a2,3Gal{31,4GlcNAc{31,2Mana, respectively, because of differences in the complement of glycosyltransferases expressed in pituitary and placenta.
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