The oligomerization of a family of four genetically clustered human gastrointestinal mucins

• Published in: Glycobiology (Oxford) 1998-01, Vol.8 (1), p.67-75
• Main Authors: van Klinken, B.Jan-Willem, Einerhand, Alexandra W.C., Büller, Hans A., Dekker, Jan
• Format: Article
• Language: English
• Subjects: biosynthesis; Cell Line; Chromosomes, Human, Pair 11 - genetics; Dimerization; Endoplasmic Reticulum, Rough - chemistry; Gastric Mucins - chemistry; Gastric Mucins - genetics; Gastric Mucosa - chemistry; Glycosylation; Humans; Intestinal Mucosa - chemistry; LS174T cell line; Mucin 5AC; Mucin-2; Mucin-5B; Mucin-6; mucins; Mucins - chemistry; Mucins - genetics; Multigene Family; oligomerization; Protein Conformation; Protein Precursors - chemistry; Protein Precursors - genetics
• ISSN: 0959-6658; 1460-2423
• DOI: 10.1093/glycob/8.1.67

Mucins are synthesized and secreted by many epithelia. They are complex glycoproteins that offer cytoprotection. In their functional configuration, mucins form oligomers by a biosynthetic process that is poorly understood. A family of four human gastrointestinal mucin genes (MUC2, MUC5AC, MUC5B, and MUC6) is clustered to chromosome 11p15.5. To study oligomerization of these related mucins, we performed metabolic labeling experiments with [35S]amino acids in LS174T cells, and isolated mucin precursors by specific immunoprecipitations that were analyzed on SDS-PAGE. Each of the precursors of MUC2, MUC5AC, MUC5B, and MUC6 formed a single species of disulfide-linked homooligomer within 1 h after pulse labeling. Based on apparent molecular masses, these oligomeric precursors were most likely dimers. Inhibition of vesicular RER-to-Golgi transport, with brefeldin A and CCCP, did not affect the dimerization of MUC2 precursors, localizing dimerization to the RER. O-Glycosylation of MUC2 followed dimerization. Inhibition of N-glycosylation by tunicamycin retarded, but did not inhibit, dimerization, indicating that N-glycans play a role in efficient dimerization of MUC2 precursors. Based on sequence homology, the ability of MUC2, MUC5AC, MUC5B and MUC6 to dimerize most likely resides in their C-terminal domains. Thus, the RER-localized dimerization of secretory mucins likely proceeds by similar mechanisms, which is an essential step in the formation of the human gastrointestinal mucus-gels.