Cytokeratin 13 contains O-glycosidically linked N-acetylglucosamine residues.
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.
King
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IA
Dermatology Research Group, Medical Research Council Clinical Research Center, Harrow, United Kingdom.
Hounsell
E F
EF
D000117:Acetylglucosamine / Q000302:isolation & purification* / Q000378:metabolism; D000818:Animals; D002236:Carbohydrate Conformation; D002294:Carcinoma, Squamous Cell / Q000032:analysis; D002460:Cell Line; D002478:Cells, Cultured; D005944:Glucosamine / Q000031:analogs & derivatives*; D006027:Glycosides / Q000378:metabolism*; D006801:Humans; D007624:KB Cells / Q000032:analysis; D007633:Keratins / Q000302:isolation & purification* / Q000378:metabolism; D051379:Mice; D012867:Skin
D006027:Glycosides; D007633:Keratins; D005944:Glucosamine; D000117:Acetylglucosamine