Claudins are a family of proteins which, along with occludin, are the most important components of the tight junctions (zonulae occludentes). Tight junctions establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium. They have four transmembrane domains, with the N-terminus and the C-terminus in the cytoplasm.
Claudins are small (20–24/27 kilodalton (kDa)) transmembrane proteins which are found in many organisms, ranging from nematodes to human beings. They all have a very similar structure, although this structural conservation is not observed on the genetic level. Claudins span the cellular membrane 4 times, with the N-terminal end and the C-terminal end both located in the cytoplasm, and two extracellular loops which show the highest degree of conservation. The first extracellular loop consists on average of 53 amino acids and the second one, being slightly smaller, of 24 amino acids. The N-terminal end is usually very short (4–10 amino acids), the C-terminal end varies in length from 21 to 63 and is necessary for the localisation of these proteins in the tight junctions. It is suspected that the cysteines of individual or separate claudins form disulfide bonds. All human claudins (with the exception of Claudin 12) have domains that let them bind to PDZ domains of scaffold proteins.
Claudins create both cis and trans strand formation between cell membranes.
Claudins were first named in 1998 by Japanese researchers Mikio Furuse and Shoichiro Tsukita at Kyoto University. The name claudin comes from Latin word claudere ("to close"), suggesting the barrier role of these proteins.
- CLDN1, CLDN2, CLDN3, CLDN4, CLDN5, CLDN6, CLDN7, CLDN8, CLDN9, CLDN10, CLDN11, CLDN12, CLDN13, CLDN14, CLDN15, CLDN16, CLDN17, CLDN18, CLDN19, CLDN20, CLDN21, CLDN22, CLDN23
- Hou, Jianghui; Konrad, Martin (2010-01-01), L. Yu, Alan S. (ed.), "Chapter 7 - Claudins and Renal Magnesium Handling", Current Topics in Membranes, Academic Press, 65, pp. 151–176, doi:10.1016/s1063-5823(10)65007-7, retrieved 2020-10-22
- Furuse, Mikio (2010-01-01), L. Yu, Alan S. (ed.), "Chapter 1 - Introduction: Claudins, Tight Junctions, and the Paracellular Barrier", Current Topics in Membranes, Academic Press, 65, pp. 1–19, doi:10.1016/s1063-5823(10)65001-6, retrieved 2020-10-22
- Szaszi, Katalin; Amoozadeh, Yasaman (2014-01-01), Jeon, Kwang W. (ed.), "Chapter Six - New Insights into Functions, Regulation, and Pathological Roles of Tight Junctions in Kidney Tubular Epithelium", International Review of Cell and Molecular Biology, Academic Press, 308, pp. 205–271, doi:10.1016/b978-0-12-800097-7.00006-3, retrieved 2020-10-22
- Greene, Chris; Campbell, Matthew; Janigro, Damir (2019-01-01), Lonser, Russell R.; Sarntinoranont, Malisa; Bankiewicz, Krystof (eds.), "Chapter 1 - Fundamentals of Brain–Barrier Anatomy and Global Functions", Nervous System Drug Delivery, Academic Press, pp. 3–20, doi:10.1016/b978-0-12-813997-4.00001-3, ISBN 978-0-12-813997-4, retrieved 2020-10-22
- Rüffer C, Gerke V (May 2004). "The C-terminal cytoplasmic tail of claudins 1 and 5 but not its PDZ-binding motif is required for apical localization at epithelial and endothelial tight junctions". Eur. J. Cell Biol. 83 (4): 135–44. doi:10.1078/0171-9335-00366. PMID 15260435.
- Haseloff, Reiner F.; Piontek, Jörg; Blasig, Ingolf E. (2010-01-01), L. Yu, Alan S. (ed.), "Chapter 5 - The Investigation of cis- and trans-Interactions Between Claudins", Current Topics in Membranes, Academic Press, 65, pp. 97–112, doi:10.1016/s1063-5823(10)65005-3, retrieved 2020-10-22
- Furuse M, Fujita K, Hiiragi T, Fujimoto K, Tsukita S (June 1998). "Claudin-1 and -2: novel integral membrane proteins localizing at tight junctions with no sequence similarity to occludin". J. Cell Biol. 141 (7): 1539–50. doi:10.1083/jcb.141.7.1539. PMC 2132999. PMID 9647647.
- Liu F, Koval M, Ranganathan S, Fanayan S, Hancock WS, Lundberg EK, Beavis RC, Lane L, Duek P, McQuade L, Kelleher NL, Baker MS (Dec 2015). "A systems proteomics view of the endogenous human claudin protein family". J Proteome Res. 15 (2): 339–359. doi:10.1021/acs.jproteome.5b00769. PMC 4777318. PMID 26680015.
- Hou, Jianghui (2019-01-01), Hou, Jianghui (ed.), "Chapter 7 - Paracellular Channel in Organ System", The Paracellular Channel, Academic Press, pp. 93–141, doi:10.1016/b978-0-12-814635-4.00007-3, ISBN 978-0-12-814635-4, retrieved 2020-10-22
- Hou, Jianghui (2019-01-01), Hou, Jianghui (ed.), "Chapter 8 - Paracellular Channel in Human Disease", The Paracellular Channel, Academic Press, pp. 143–173, doi:10.1016/b978-0-12-814635-4.00008-5, ISBN 978-0-12-814635-4, retrieved 2020-10-22