Cytokeratin 13 contains O-glycosidically linked N-acetylglucosamine residues.

I. A. King,E. Hounsell

Published 1989 in Journal of Biological Chemistry

ABSTRACT

The glycosylation of human cytokeratins was investigated in cultured human keratinocytes and A431 cells by metabolic labeling with [3H]glucosamine. In the presence of tunicamycin, keratinocytes incorporated [3H]glucosamine into a vitamin A-regulated acidic 53-kDa component of the cytoskeleton which was identified as cytokeratin 13 by one- and two-dimensional immunoblotting with specific monoclonal antibodies. This cytoskeletal component was also labeled with [3H]glucosamine in A431 cells but not in KB cells, which do not express cytokeratin 13. Its labeling was resistant to tunicamycin, suggesting that [3H]glucosamine had not been incorporated into N-linked oligosaccharides. Acid hydrolysis followed by paper and ion-exchange chromatography showed that the radioactivity in electrophoretically purified cytokeratin 13 was still present as glucosamine. Radioactivity was completely removed by treatment with beta-N-acetylglucosaminidase, suggesting that it was present in terminal N-acetylglucosamine residues. The labeled carbohydrate was released by alkaline borohydride treatment and was bound by a phenylboronic acid column, indicating an O-glycosidic linkage. On Bio-Gel P-2 columns, the beta-eliminated carbohydrate co-eluted with authentic N-acetylglucosaminitol. The results indicate that cytokeratin 13 contains single residues of N-acetylglucosamine O-glycosidically linked to the polypeptide chain.

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