Evidence for a second peptide cleavage in the C-terminal domain of rodent intestinal mucin Muc3.

Rat intestinal mucin Muc3 (rMuc3), like its human homologue (MUC3) and several other membrane mucins, contains a C-terminally located SEA (sea urchin sperm protein, enterokinase and agrin) module, with an intrinsic proteolytic site sequence G downward arrow SIVV (where G downward arrow S is the glycine serine cleavage site). As shown previously [Wang, Khatri and Forstner (2002) Biochem. J.

N-linked oligosaccharides play a role in disulphide-dependent dimerization of intestinal mucin Muc2.

Within the C-terminal domain of many secretory mucins is a 'cystine knot' (CK), which is needed for dimer formation in the endoplasmic reticulum. Previous studies indicate that in addition to an unpaired cysteine, the three intramolecular cystine bonds of the knot are important for stability of the dimers formed by rat intestinal mucin Muc2. The present study was undertaken to determine whether the two N-glycans N9 and N10, located near the first and second cysteines of the knot, also play a role in dimer formation.

Effect of chondroitinase ABC on purulent sputum from cystic fibrosis and other patients.

Cystic fibrosis (CF) patients develop chronic lung infections associated with airway obstruction by viscous and insoluble mucus secretions. Although mucus glycoproteins (mucins) are thought to be responsible for mucus plugs, other glycoconjugate components of airway secretions have not been systematically evaluated. The aim of the present study was to determine whether chondroitin sulfate proteoglycans (CSPG) contribute to the insolubility of CF sputum.

SEA (sea-urchin sperm protein, enterokinase and agrin)-module cleavage, association of fragments and membrane targeting of rat intestinal mucin Muc3.

In a previous study we showed, by transient expression studies in COS-1 cells, that the C-terminal domain of rat intestinal membrane mucin Muc3 was cleaved between glycine and serine within a GSIVV (one-letter) amino acid sequence during its residence in the endoplasmic reticulum. The extracellular domain fragment remained linked to the membrane-associated fragment by non-covalent interactions. The present study demonstrates that cleavage depends not only on the presence of the G/SIVV site (where G/S is the glycine downward arrow serine cleavage site), but also on more distant C-terminal sequences in the SEA (sea-urchin sperm protein, enterokinase and agrin) module.

C-terminal domain of rodent intestinal mucin Muc3 is proteolytically cleaved in the endoplasmic reticulum to generate extracellular and membrane components.

Although human MUC3 and rodent Muc3 are both membrane-associated intestinal mucins, the present study has explored the possibility that rodent Muc3 might exist in soluble as well as membrane forms. No evidence was obtained for the existence of soluble splice variants; however, experiments with heterologous cells transfected with cDNA encoding the 381-residue C-terminal domain of rodent Muc3 showed that a definitive proteolytic cleavage occurs during processing in the endoplasmic reticulum. The products consisted of a V5-tagged 30 kDa extracellular glycopeptide and a Myc-tagged 49 kDa membrane-associated glycopeptide.