Mucin 1228983 216365118 2008-06-01T08:56:02Z 79.16.113.168 '''Mucins''' are a family of large, heavily [[glycosylation|glycosylated]] [[proteins]] ([[glycoconjugate]]s).<ref>{{Dorlands|m_21|12544036}}</ref> Although some mucins are [[cell membrane|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]]. ==Glycosylation and aggregation== Mucin [[gene]]s encode mucin [[monomers]] that are synthesized as rod-shape [[apomucin]] cores that are post-translationally modified by exceptionally abundant [[glycosylation]]. The dense "sugar coating" of mucins gives them considerable [[hygroscopic|water-holding]] capacity and also makes them resistant to [[proteolysis]], which may be important in maintaining [[mucous membrane|mucosal]] barriers. Mucins are secreted as massive [[aggregate]]s of proteins with molecular masses of roughly 1 to 10 million Da. Within these [[aggregate]]s, [[monomer]]s are linked to one another mostly by non-[[covalent]] interactions, although intermolecular [[disulfide]] bonds may also play a role in this process. ==Regions== Two distinctly different regions are found in mature mucins: * The amino- and carboxy-terminal regions are very lightly glycosylated, but rich in [[cysteine]]s, 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 acid]]s are [[serine]] or [[threonine]]. This area becomes saturated with hundreds of [[Glycosylation#O-linked glycosylation|O-linked]] [[oligosaccharides]]. [[Glycosylation#N-linked glycosylation|N-linked]] [[oligosaccharides]] are also found on mucins, but much less abundantly. ==Genes== At least 19 human mucin genes have been distinguished by cDNA cloning — [[MUC1]], [[MUC2]], [[MUC3A]], [[MUC3B]], [[MUC4]], [[MUC5AC]], [[MUC5B]], [[MUC6]], [[MUC7]], [[MUC8]], [[MUC12]], [[MUC13]], [[MUC15]], [[MUC16]], [[MUC17]], [[MUC19]], and [[MUC20]]. The major secreted airway mucins are [[MUC5AC]] and [[MUC5B]], while [[MUC2]] is secreted mostly in the intestine but also in the airway. ==Clinical significance== Increased mucin production occurs in many [[adenocarcinoma]]s, including cancer of the pancreas, lung, breast, ovary, colon, etc. Mucins are also overexpressed in lung diseases such as [[asthma]], [[bronchitis]], [[COPD]] or [[cystic fibrosis]]. Two membrane mucins, MUC1 and MUC4 have been extensively studied in relation to their pathological implication in the disease process.<ref>Singh, A.P. et al. "Inhibition of MUC4 expression suppresses pancreatic tumor cell growth and metastasis." Cancer Research 2004 Jan 15;64(2):622-30. PMID 14744777</ref><ref>Singh, A.P. et al. "Aberrant expression of transmembrane mucins, MUC1 and MUC4, in human prostate carcinomas". Prostate. 2006 Mar 1;66(4):421-9. PMID 16302265</ref><ref>Singh, A.P. et al. "Emerging roles of MUC4 in cancer: a novel target for diagnosis and therapy." Cancer Research 2007 Jan 15, 67(2):433-6. PMID 17234748</ref> Moreover, mucins are also being investigated for their potential as diagnostic markers. ==References== <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 ==External links== * {{MeshName|Mucins}} {{Mucoproteins}} [[Category:Proteins]] [[cs:Mucin]] [[de:Muzine]] [[fr:Mucine]] [[it:Mucina]] [[ja:ムチン]] [[fi:Musiini]]