Respiratory tract mucins: structure and expression patterns.
Goblet cells produce mainly MUC5AC, but also MUC5B and some MUC2 in apparently 'irritated' airways. MUC5B dominates in the submucosal glands although a little MUC5AC and MUC7 are usually present. MUC4 originates from the ciliated cells. After separation into a gel and a sol phase, lysozyme and lactoferrin are enriched in the salivary gel phase suggesting that mucus may act as a matrix for 'protective' proteins on the mucosal surface. A salivary MUC5B N-terminal fragment consistent with a cleavage event in the D' domain was detected with antibodies against various N-terminal peptide sequences suggesting that assembly of MUC5B occurs through a mechanism similar to that of the von Willebrand factor. Identification of additional cleavage sites C-terminal to the D' domain suggests that most of the N-terminal low-glycosylated part of MUC5B may be removed without affecting the oligomeric nature of the mucin. Possibly, the generation of mucins with different macromolecular properties through proteolytic 'processing' is one way of adapting the mucus polymer matrix to meet local physiological demands. Monomeric mucins that appear to turn over rapidly in the airway epithelium have been identified using radiolabelled mucin precursors. 'Shedding' of such mucins after microbe attachment may prevent colonization of epithelial surfaces.
Davies
Julia R
JR
Mucosal Biology Group, Department of Cell and Molecular Biology, Lund University, BMC, C13, 5-22184, Lund, Sweden.
Herrmann
Annkatrin
A
Russell
Wayne
W
Svitacheva
Naila
N
Wickström
Claes
C
Carlstedt
Ingemar
I
D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D010450:Endopeptidases / Q000378:metabolism; D005088:Exocrine Glands / Q000378:metabolism; D005089:Exocytosis; D005782:Gels; D005786:Gene Expression Regulation; D006031:Glycosylation; D006801:Humans; D009077:Mucins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D011110:Polymorphism, Genetic; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D012137:Respiratory System / Q000378:metabolism*; D012471:Salivary Proteins and Peptides / Q000737:chemistry / Q000378:metabolism; D014783:Viscosity
D018076:DNA, Complementary; D005782:Gels; D009077:Mucins; D012471:Salivary Proteins and Peptides; D010450:Endopeptidases