An intrinsic membrane glycoprotein with cytosolically oriented n-linked sugars.
We demonstrate that the Na(+)-pump alpha-subunit polypeptide is glycosylated by using bovine milk galactosyltransferase, a specific enzyme which attaches galactose to terminal N-acetylglucosamine residues. The galactose acceptor sites are available for glycosylation only after permeabilization of right-side-out vesicles prepared from kidney outer medulla; therefore, the oligosaccharide moieties are facing the cytoplasm of the cell. We further show that the oligosaccharides are bound to asparagine residues of the alpha-subunit polypeptide, since the protein-carbohydrate linkage is hydrolyzed by peptide-N glycosidase F (an enzyme specific for N-linked sugars). Thus, the Na(+)-pump alpha subunit is a glycoprotein with its N-linked oligosaccharide moieties located at the cytosolic face of the cell membrane. Intrinsic membrane glycoproteins with such an oligosaccharide-protein linkage and cell membrane orientation have not been previously reported, to our knowledge.[1]References
- An intrinsic membrane glycoprotein with cytosolically oriented n-linked sugars. Pedemonte, C.H., Sachs, G., Kaplan, J.H. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
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