Summary: Tight junction protein, Claudin-like
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This is the Wikipedia entry entitled "Claudin". More...
Claudin Edit Wikipedia article
Claudins are a family of proteins that are the most important components of the tight junctions, where they 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.
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[edit] Structure
Claudins are small (20â27 kilodalton (kDa)) transmembrane proteins which are found in many organisms, ranging from nematodes to human beings, and are very similar in their structure, although this 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 (4â10 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.[1] 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.
[edit] History
Claudins were first named in 1998 by Japanese researchers Mikio Furuse and Shoichiro Tsukita at Kyoto University.[2] The name claudin comes from Latin word claudere ("to close"), suggesting the barrier role of these proteins.
[edit] Genes
In humans, 24 members of the family have been described.
- CLDN1, CLDN2, CLDN3, CLDN4, CLDN5, CLDN6, CLDN7, CLDN8, CLDN9, CLDN10, CLDN11, CLDN12, CLDN13, CLDN14, CLDN15, CLDN16, CLDN17, CLDN18, CLDN19, CLDN20, CLDN21, CLDN22, CLDN23
[edit] See also
[edit] Additional images
[edit] References
- ^ 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): 135â44. PMID 15260435.
- ^ 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): 1539â50. doi:10.1083/jcb.141.7.1539. PMC 2132999. PMID 9647647.Wikilink embedded in URL title (help)
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This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.
This is the Wikipedia entry entitled "Tight junction". More...
Tight junction Edit Wikipedia article
| Tight junction | |
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| Diagram of Tight junction | |
| Latin | junctio occludens |
| Code | TH H1.00.01.1.02007 |
Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates. The corresponding junctions that occur in invertebrates are septate junctions.
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[edit] Structure
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This section does not cite any references or sources. (September 2012) |
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. Although more proteins are present, the major types are the claudins and the occludins. These associate with different peripheral membrane proteins located on the intracellular side of plasma membrane, which anchor the strands to the actin component of the cytoskeleton. Thus, tight junctions join together the cytoskeletons of adjacent cells.
[edit] Functions
They perform vital functions:
- They hold cells together.
- Barrier function, which can be further subdivided into protective barriers and functional barriers serving purposes such as material transport and maintenance of osmotic balance:
- They help to maintain the 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 aims to preserve the transcellular transport.
- They prevent the passage of molecules and ions through the space between cells. So materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue. This pathway provides control over what substances are allowed through. (Tight junctions play this role in maintaining the bloodâbrain barrier.) At 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 is proposed: large slit breaks formed by infrequent discontinuities in the TJ complex and numerous small circular pores.[1]
In human physiology there are two main types of epithelia using distinct types of barrier mechanism. Dermal structures such as skin form a barrier from many layers of keratinised squamous cells. Internal epithelia on the other hand more often rely on tight cells junctions for their barrier function. This kind of barriers is mostly formed by only one or two layers of cells. Until recently it was not clear whether tight cell junctions also play any role in the barrier function of the skin and similar external epithelia, recent research suggests that this is indeed the case.
[edit] Classification
Epithelia are classed as 'tight' or 'leaky' depending on the ability of the tight junctions to prevent water and solute movement:
- Tight epithelia have tight junctions that prevent most movement between cells. An example of a tight epithelium is the distal convoluted tubule, and the collecting duct part of the nephron in the kidney.
- Leaky epithelia do not have these tight junctions, or have less complex tight junctions. For instance, the tight junction in the kidney proximal tubule, a very leaky epithelium, has only two to three junctional strands, and these strands exhibit infrequent large slit breaks.
[edit] See also
[edit] References
- ^ Guo, Weinbaum and Weinstein. A dual-pathway ultrastructural model for the tight junction of rat proximal tubule epithelium. Am. J. Physiol.: Renal Physiol., 285: F241-F257, 2003
[edit] External links
- An Overview of the Tight Junction at Zonapse.Net
- Occludin in Focus at Zonapse.Net
- Tight Junctions at the US National Library of Medicine Medical Subject Headings (MeSH)
- BU Histology Learning System: 20502loa
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This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Tight junction protein, Claudin-like Provide feedback
This is a family of probable membrane tight junction, Claudin-like, proteins.
Internal database links
| Similarity to PfamA using HHSearch: | Clc-like L_HGMIC_fpl Claudin_2 |
External database links
| PANDIT: | PF06653 |
| Pseudofam: | PF06653 |
| SYSTERS: | Claudin_3 |
Domain organisation
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
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Pfam Clan
This family is a member of clan Transporter (CL0375), which contains the following 10 members:
Amastin Claudin_2 Claudin_3 Clc-like DUF3185 Fig1 GSG-1 L_HGMIC_fpl PMP22_Claudin SUR7Alignments
We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the NCBI sequence database, and our metagenomics sequence database. More...
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| Seed (24) |
Full (100) |
Representative proteomes | NCBI (107) |
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| RP15 (31) |
RP35 (34) |
RP55 (96) |
RP75 (96) |
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| PP/heatmap | 1 | |||||||
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We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
| Seed (24) |
Full (100) |
Representative proteomes | NCBI (107) |
Meta (0) |
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| RP15 (31) |
RP35 (34) |
RP55 (96) |
RP75 (96) |
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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
External links
MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.
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Note: You can also download the data file for the tree.
Curation and family details
This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.
Curation
| Seed source: | Pfam-B_21553 (release 10.0) |
| Previous IDs: | DUF1164; |
| Type: | Family |
| Author: | Moxon SJ, Coggill P |
| Number in seed: | 24 |
| Number in full: | 100 |
| Average length of the domain: | 156.80 aa |
| Average identity of full alignment: | 19 % |
| Average coverage of the sequence by the domain: | 88.16 % |
HMM information
| HMM build commands: |
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
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| Model details: |
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| Model length: | 164 | ||||||||||||
| Family (HMM) version: | 6 | ||||||||||||
| Download: | download the raw HMM for this family |
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