Human MUC5AC mucin dimerizes in the rough endoplasmic reticulum, similarly to the MUC2 mucin.
Biosynthetic studies on the human MUC5AC mucin were performed by immunoprecipitations with antisera recognizing only the non-O-glycosylated apomucin in the colon adenocarcinoma cell line LS 174T. Pulse-chase studies and subcellular fractionations showed that MUC5AC formed dimers in the rough endoplasmic reticulum within 15 min of the initiation of biosynthesis. No non-O-glycosylated species larger than dimers were identified. The dimerization was N-glycosylation-dependent, because tunicamycin treatment significantly lowered the rate of dimerization. When the biosynthesis of MUC5AC apomucin was compared with that of MUC2 apomucin, also produced in the LS 174T cell line, both apomucins were assembled in similar ways with respect to their rates of dimerization with and without inhibition of N-glycosylation. No heterodimerization was observed between the human MUC5AC and the MUC2 apomucins despite the extensive sequence similarities in the positions of the cysteine residues in the C-termini proposed to be involved in mucin dimerization.
Asker
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N
Department of Medical Biochemistry, Göteborg University, Medicinaregatan 9A, S-413 90 Gothenburg, Sweden.
Axelsson
M A
MA
Olofsson
S O
SO
Hansson
G C
GC
D000595:Amino Acid Sequence; D000818:Animals; D001671:Biochemistry / Q000379:methods; D002277:Carcinoma / Q000737:chemistry / Q000378:metabolism; D003110:Colonic Neoplasms / Q000737:chemistry / Q000378:metabolism; D003429:Cross Reactions; D019281:Dimerization; D018870:Endoplasmic Reticulum, Rough / Q000378:metabolism*; D005752:Gastric Mucins / Q000276:immunology / Q000378:metabolism; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D007106:Immune Sera; D008969:Molecular Sequence Data; D055271:Mucin 5AC; D055262:Mucin-2; D009077:Mucins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D011817:Rabbits; D013347:Subcellular Fractions; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology; D014461:Ultracentrifugation
D005752:Gastric Mucins; D007106:Immune Sera; C524625:MUC2 protein, human; C524678:MUC5AC protein, human; D055271:Mucin 5AC; D055262:Mucin-2; D009077:Mucins; C053366:apomucin; D014415:Tunicamycin