Biosynthesis of human colonic mucin: Muc2 is the prominent secretory mucin

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Abstract

Background/Aims: Human colonic epithelium produces large amounts of mucin. The aim of this study was to examine mucin biosynthesis in the human colon. Methods: Human colonic mucin was isolated using CsCI density gradients, and polyclonal antiserum was raised. Biosynthesis of colonic mucins was studied by labeling colonic explants with 35S-labeled amino acids or [35S]sulfate and subsequent immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Results: The polyclonal antiserum specifically recognized colonic mucin, primarily reacting with peptide epitopes. Biosynthetic pulse/ chase experiments showed a 35S-amino acid-labeled mucin precursor of about 600 kilodaltons, which was converted into a mature, glycosylated, and sulfated mucin and subsequently secreted into the medium. This mature mucin comigrated with isolated colonic mucin with an apparent molecular weight of 550 kilodaltons on SDS-PAGE, whereas gel filtration indicated that the molecular weight is actually much larger. Independent immunoprecipitation with an anti-Muc2 antiserum showed cross-reactivity with the 600-kilodalton precursor. Conclusions: These results show the biosynthesis of a secretory colonic mucin for the first time. This mucin is synthesized as a precursor protein of approximately 600 kilodaltons, which, after glycosylation, is secreted as a glycoprotein with an apparent molecular weight of 550 kilodaltons on SDS-PAGE. It is very likely that this mucin is Muc2. © 1994.

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Tytgat, K. M. A. J., Büller, H. A., Opdam, F. J. M., Kim, Y. S., Einerhand, A. W. C., & Dekker, J. (1994). Biosynthesis of human colonic mucin: Muc2 is the prominent secretory mucin. Gastroenterology, 107(5), 1352–1363. https://doi.org/10.1016/0016-5085(94)90537-1

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