Biosynthesis of human colonic mucin: Muc2 is the prominent secretory mucin.
OBJECTIVE
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 CsCl 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.
Tytgat
K M
KM
Department of Pediatric Gastroenterology and Nutrition, Academic Medical Center, Amsterdam, The Netherlands.
Büller
H A
HA
Opdam
F J
FJ
Kim
Y S
YS
Einerhand
A W
AW
Dekker
J
J
D003106:Colon / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006031:Glycosylation; D006801:Humans; D007106:Immune Sera; D007413:Intestinal Mucosa / Q000378:metabolism; D008970:Molecular Weight; D055262:Mucin-2; D009077:Mucins / Q000032:analysis / Q000096:biosynthesis* / Q000378:metabolism; D011233:Precipitin Tests; D011498:Protein Precursors / Q000096:biosynthesis
D007106:Immune Sera; C524625:MUC2 protein, human; D055262:Mucin-2; D009077:Mucins; D011498:Protein Precursors