The Interaction of Large Bowel Microflora with the Colonic Mucus Barrier

Figure 1

Major posttranscriptional steps involved in colonic mucin synthesis and secretion. (1) MUC gene products are translated at the rough endoplasmic reticulum. (2) MUC gene products are then N-glycosylated and dimerised at the C-terminal. (3) The N-glycosylation is necessary for mucins to be transferred to the Golgi apparatus for further processing. Within the Golgi apparatus, mucins are O-glycosylated and polymerised by disulphide bridge formation between cysteine-rich N-terminal sections of the polypeptide backbone. Polymeric mucins become tightly packed due to the presence of high concentrations of calcium ions. (4) The resulting mucin granules are externalised by the goblet cells via exocytosis. (5) Following release, mucin granules rapidly unfurl into a viscoelastic mucus gel bilayer (adapted from details given in [23, 45, 46]).