Mucins are a family of large, heavily glycosylated proteins. Although some mucins are membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, the concentration here is on those mucins that are secreted on mucosal surfaces and saliva. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouths of some animals, including humans. ...

Mucin genes encode mucin monomers that are synthesized as rod-shape apomucin cores that are post-translationally modified by exceptionally abundant glycosylation. Two distinctly different regions are found in mature mucins: This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Glycosylation is the process or result of addition of saccharides to proteins and lipids. ...

• The amino- and carboxy-terminal regions are very lightly glycosylated, but rich in cysteines, which are likely involved in establishing disulfide linkages within and among mucin monomers.

• A large central region formed of multiple tandem repeats of 10 to 80 residue sequences in which up to half of the amino acids are serine or threonine. This area becomes saturated with hundreds of O-linked oligosaccharides. N-linked oligosaccharides are also found on mucins, but much less abundantly.

The dense "sugar coating" of mucins gives them considerable water-holding capacity and also makes them resistant to proteolysis, which may be important in maintaining mucosal barriers. Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins, though only in small quantities. ... In chemistry, a disulfide is an ion formed by sulfur atoms. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... Serine is one of the 20 natural amino acids. ... Threonine is one of the 20 natural amino acids. ... Glycosylation is the process or result of addition of saccharides to proteins and lipids. ... The term “oligosaccharide” refers to a short chain of sugar molecules (“oligo” means “few” and “saccharide” means “sugar. ... Glycosylation is the process or result of addition of saccharides to proteins and lipids. ... The term “oligosaccharide” refers to a short chain of sugar molecules (“oligo” means “few” and “saccharide” means “sugar. ... A hygroscopic substance is a substance that absorbs water readily from its surroundings. ... Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... The mucous membranes (or mucosae; singular: mucosa) are linings of ectodermic origin, covered in epithelium, and are involved in absorption and secretion. ...

Mucins are secreted as massive aggregates of proteins with molecular masses of roughly 1 to 10 million Da. Within these aggregates, monomers are linked to one another mostly by non-covalent interactions, although intermolecular disulfide bonds may also play a role in this process. At least 19 human mucin genes have been distinguished by cDNA cloning--MUC1, 2, 3A, 3B, 4, 5AC, 5B, 6-9, 11-13, and 15-19. The major secreted airway mucins are MUC5AC and MUC5B, while MUC2 is secreted mostly in the intestine but also in the airway. Look up Aggregate in Wiktionary, the free dictionary. ... Look up Aggregate in Wiktionary, the free dictionary. ... In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... In chemistry, a disulfide is an ion formed by sulfur atoms. ...

Increased mucin production occurs in Adenocarcinoma, a type of lung cancer, and in lung diseases such as asthma, bronchitis, COPD or cystic fibrosis. In medicine, carcinoma is any cancer that arises from epithelial cells. ... Bronchitis is an obstructive pulmonary disease characterized by inflammation of the bronchi of the lungs. ... Chronic obstructive pulmonary disease (COPD) is an umbrella term for a group of respiratory tract diseases that are characterised by airflow obstruction or limitation. ...

References

Ali, M.S., et al. "Major secretory mucin expression in chronic sinusitis." Otolaryngol Head Neck Surg. 2005 Sep; 133(3); 423-8. PMID: 16143194

Perez-Vilar, J. and Hill, R. L. Mucin Family of Glycoproteins. Encyclopedia of Biological Chemistry (Lennarz & Lane, EDs.) Academic Press/Elsevier, Oxford, 2004, vol. 2, pp 758-764