Tight junctions , also known as occluding junctions or zonulae occludentes (singular, zonula occludens ), are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epithelial cells . They also play a critical role maintaining the structure and permeability of endothelial cells . Tight junctions may also serve as leaky pathways by forming selective channels for small cations, anions, or water. The corresponding junctions that occur in invertebrates are septate junctions .
12-584: (Redirected from L-27 ) L27 or L-27 may refer to: L27 domain , a protein domain 60S ribosomal protein L27 Buick L27 engine , a V6 automobile engine Cessna L-27 , a light utility aircraft of the U.S. Air Force HMS L27 , a submarine of the Royal Navy HMS ; Hastings (L27) , a sloop of the Royal Navy Klemm L 27 ,
24-563: A German training aircraft Lectionary 27 , a medieval Greek manuscript [REDACTED] Topics referred to by the same term This disambiguation page lists articles associated with the same title formed as a letter–number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=L27&oldid=1090686851 " Category : Letter–number combination disambiguation pages Hidden categories: Short description
36-539: A tight, four-helix bundle in the heterodimer , whilst the third helix of each L27_2 domain forms another four-helix bundle that assembles the two units of the heterodimer into a tetramer . The L27_N domain is often found at the N-terminus of the L27 domain. It plays a role in the biogenesis of tight junctions and in the establishment of cell polarity in epithelial cells . Each L27_N domain consists of three alpha-helices,
48-523: Is a stub . You can help Misplaced Pages by expanding it . Tight junction Tight junctions are composed of a branching network of sealing strands, each strand acting independently from the others. Therefore, the efficiency of the junction in preventing ion passage increases exponentially with the number of strands. Each strand is formed from a row of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly. There are at least 40 different proteins composing
60-541: Is different from Wikidata All article disambiguation pages All disambiguation pages L27 domain The L27 domain is a protein domain that is found in receptor targeting proteins Lin-2 and Lin-7 ( LIN7A , LIN7B , LIN7C ), as well as some protein kinases and human MPP2 protein. The L27 domain is a protein interaction module that exists in a large family of scaffold proteins, functioning as an organisation centre of large protein assemblies required for
72-498: The apicobasal polarity of cells by preventing the lateral diffusion of integral membrane proteins between the apical and lateral/basal surfaces, allowing the specialized functions of each surface (for example receptor-mediated endocytosis at the apical surface and exocytosis at the basolateral surface) to be preserved. This allows polarized transcellular transport and specialized functions of apical and basolateral membranes. Epithelia are classed as "tight" or "leaky", depending on
84-516: The cytoskeletons of adjacent cells. Investigation using freeze-fracture methods in electron microscopy is ideal for revealing the lateral extent of tight junctions in cell membranes and has been useful in showing how tight junctions are formed. Tight junctions provide endothelial and epithelial cells with barrier function, which can be further subdivided into protective barriers and functional barriers serving purposes such as material transport and maintenance of osmotic balance. Tight junctions prevent
96-788: The establishment and maintenance of cell polarity. L27 domains form specific heterotetrameric complexes, in which each domain contains three alpha-helices . The L27_2 domain is a protein-protein interaction domain capable of organising scaffold proteins into supramolecular assemblies by formation of heteromeric L27_2 domain complexes. L27_2 domain-mediated protein assemblies have been shown to play essential roles in cellular processes including asymmetric cell division , establishment and maintenance of cell polarity , and clustering of receptors and ion channels . Members of this family form specific heterotetrameric complexes, in which each domain contains three alpha-helices . The two N-terminal helices of each L27_2 domain pack together to form
108-467: The first two of which form an antiparallel coiled-coil . Two L27 domains come together to form a four-helical bundle with the antiparallel coiled-coils formed by the first two helices . The third helix of each domain forms another coiled-coil packing at one end of the four-helix bundle, creating a large hydrophobic interface: the hydrophobic interactions are the major force that drives heterodimer formation. This protein -related article
120-405: The passage of molecules and ions through the intercellular space of adjacent cells, so materials must actually enter the cells (by diffusion or active transport ) in order to pass through the tissue. The constrained intracellular pathway exacted by the tight junction barrier system allows precise control over which substances can pass through a particular tissue (e.g. the blood–brain barrier ). At
132-413: The present time, it is still unclear whether the control is active or passive and how these pathways are formed. In one study for paracellular transport across the tight junction in kidney proximal tubule, a dual pathway model was proposed, consisting of large slit breaks formed by infrequent discontinuities in the tight junction complex and numerous small circular pores. Tight junctions also help maintain
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#1732844108050144-455: The tight junctions. These proteins consist of both transmembrane and cytoplasmic proteins. The three major transmembrane proteins are occludin , claudins , and junction adhesion molecule ( JAM ) proteins. These associate with different peripheral membrane proteins such as ZO-1 located on the intracellular side of plasma membrane, which anchor the strands to the actin component of the cytoskeleton . In this way, tight junctions join together
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