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21-898: 2ZW3 , 3IZ1 , 3IZ2 , 5ERA , 5ER7 2706 14619 ENSG00000165474 ENSMUSG00000046352 P29033 Q00977 NM_004004 NM_008125 NP_003995 NP_032151 Gap junction beta-2 protein (GJB2), also known as connexin 26 (Cx26) — is a protein that in humans is encoded by the GJB2 gene . Gap junctions were first characterized by electron microscopy as regionally specialized structures on plasma membranes of contacting adherent cells. These structures were shown to consist of cell-to-cell channels. Proteins, called connexins , purified from fractions of enriched gap junctions from different tissues differ. The connexins are designated by their molecular mass. Another system of nomenclature divides gap junction proteins into two categories, alpha and beta, according to sequence similarities at

42-450: A gap junction. The crystal structure of the gap junction channel formed by human Cx26 (also known as GJB2) at 3.5 Å resolution is available. The density map showed the two membrane-spanning hemichannels and the arrangement of the four TMSs of the six protomers forming each hemichannel. The hemichannels feature a positively charged cytoplasmic entrance, a funnel, a negatively charged transmembrane pathway, and an extracellular cavity. The pore

63-417: Is a member of the connexin protein family and plays a crucial role in forming gap junctions, which are channels that allow the transport of nutrients, ions, and signaling molecules between adjacent cells. GJB2 is widely expressed throughout the body, with particularly important functions in the inner ear and skin. In the cochlea, GJB2 is believed to be essential for maintaining proper potassium ion levels and for

84-747: Is narrowed at the funnel, which is formed by the six amino-terminal helices lining the wall of the channel, which thus determines the molecular size restriction at the channel entrance. The connexin gene family is diverse, with twenty-one identified members in the sequenced human genome, and twenty in the mouse (nineteen of which are orthologous pairs). They usually weigh between 25 and 60 kDa, and have an average length of 380 amino acids. The various connexins have been observed to combine into both homomeric and heteromeric gap junctions, each of which may exhibit different functional properties including pore conductance, size selectivity, charge selectivity, voltage gating, and chemical gating. A remarkable aspect of connexins

105-475: Is suggested to promote cancer development by facilitating cell migration and invasion and by stimulating the self-perpetuation ability of cancer stem cells . This article on a gene on human chromosome 13 is a stub . You can help Misplaced Pages by expanding it . Connexin Connexins are commonly named according to their molecular weights, e.g. Cx26 is the connexin protein of 26 kDa. A competing nomenclature

126-401: Is that they have a relatively short half life of only a few hours. The result is the presence of a dynamic cycle by which connexins are synthesized and replaced. It has been suggested that this short life span allows for more finely regulated physiological processes to take place, such as in the myometrium . As they are being translated by ribosomes, connexins are inserted into the membrane of

147-575: Is the gap junction protein system, where connexins are sorted by their α (GJA) and β (GJB) forms, with additional connexins grouped into the C, D and E groupings, followed by an identifying number, e.g. GJA1 corresponds to Cx43. Following a vote at the Gap Junction Conference (2007) in Elsinore the community agreed to use the GJ nomenclature system for the genes that encode connexins, but wished to retain

168-512: Is the deletion of one guanine from a string of six, resulting in a frameshift and termination of the protein at amino acid number 13. Having two copies of this mutation results in deafness. Connexin 26 also plays a role in tumor suppression through mediation of the cell cycle. The abnormal expression of Cx26, correlated with several types of human cancers , may serve as a prognostic factor for cancers such as colorectal cancer, breast cancer, and bladder cancer. Furthermore, Cx26 over-expression

189-632: The ER and passing through the ERGIC , the folded connexins will usually enter the cis -Golgi network. However, some connexins, such as Cx26 may be transported independent of the Golgi. After being inserted into the plasma membrane of the cell, the hemichannels freely diffuse within the lipid bilayer. Through the aid of specific proteins, mainly cadherins , the hemichannels are able to dock with hemichannels of adjacent cells forming gap junctions. Recent studies have shown

210-834: The cytoskeleton , and the activation of intracellular signaling pathways. Thus, connexins and pannexins have multifaceted contributions to brain development and specific processes in the neuro-glio-vascular unit, including synaptic transmission and plasticity, glial signaling, vasomotor control, cell movement, and blood-brain barrier integrity in the mature CNS. Different connexins may exhibit differing specificities for solutes. For example, adenosine passed about 12-fold better through channels formed by Cx32 while AMP and ADP passed about 8-fold better, and ATP greater than 300-fold better, through channels formed by Cx43. Thus, addition of phosphate to adenosine appears to shift its relative permeability from channels formed by Cx32 to channels formed by Cx43. This may have functional consequence because

231-529: The endoplasmic reticulum (ER). It is in the ER that connexins are properly folded, yielding two extracellular loops, EL-1 and EL-2. It is also in the ER that the oligomerization of connexin molecules into hemichannels begins, a process which may continue in the UR-Golgi intermediate compartment as well. The arrangements of these hemichannels can be homotypic, heterotypic, and combined heterotypic/heteromeric. After exiting

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252-532: The channels formed by these proteins (called pannexins ) act as very large transmembrane pores that connect the intra- and extracellular compartments. Within the CNS , gap junctions provide electrical coupling between progenitor cells, neurons, and glial cells. By using specific connexin knockout mice , studies revealed that cell coupling is essential for visual signaling. In the retina , ambient light levels influence cell coupling provided by gap junction channels, adapting

273-448: The connexin nomenclature for the encoded proteins using the weight of the human protein for the numbering of orthologous proteins. Connexins contain four highly ordered transmembrane segments (TMSs), primarily unstructured C and N cytoplasmic termini, a cytoplasmic loop (CL) and two extra-cellular loops, (EL-1) and (EL-2). Connexins are assembled in groups of six to form hemichannels, or connexons, and two hemichannels then combine to form

294-2793: The development of arterial disease. Gap junction protein From Misplaced Pages, the 💕 Gap junction proteins Gap junction α (GJA) proteins GJA1 , Cx43, gap junction alpha-1 protein GJA2 , Cx38, gap junction alpha-2 protein GJA3 , Cx46, gap junction alpha-3 protein GJA4 , Cx37, gap junction alpha-4 protein GJA5 , Cx40, gap junction alpha-5 protein GJA6 , Cx33 gap junction alpha-6 protein GJA7 , Cx44.3-45.6, gap junction alpha-7 protein GJA8 , Cx50, gap junction alpha-8 protein GJA9 , Cx58, gap junction alpha-9 protein GJA10 , Cx62, gap junction alpha-10 protein GJA11 , Cx59, gap junction alpha-11 protein GJA12 , Cx46.6, gap junction alpha-12 protein Gap junction β (GJB) proteins GJB1 , Cx32, gap junction beta-1 protein GJB2 , Cx26, gap junction beta-2 protein GJB3 , Cx31, gap junction beta-3 protein GJB4 , Cx30.3, gap junction beta-4 protein GJB5 , Cx31.1, gap junction beta-5 protein GJB6 , Cx30, gap junction beta-6 protein GJB7 , Cx25, gap junction beta-7 protein Gap junction γ (GJC) proteins GJC1 , Cx45.6, gap junction gamma-1 protein GJC2 , Cx47, gap junction gamma-2 protein GJC3 , Cx29, gap junction gamma-3 protein Gap junction δ (GJD) proteins GJD1 , Cx29, gap junction delta-1 protein GJD2 , Cx36, gap junction delta-2 protein GJD3 , Cx31.9, gap junction delta-3 protein GJD4 , Cx40.1, gap junction delta-4 protein Gap junction ε (GJE) proteins GJE1 , Cx23, gap junction epsilon-1 protein See also [ edit ] Tight junction protein [REDACTED] Index of articles associated with

315-403: The energy status of a cell could be controlled via connexin expression and channel formation. The transport reaction catalyzed by connexin gap junctions is: Gap junctions are essential for many physiological processes, such as the coordinated depolarization of cardiac muscle , proper embryonic development, and the conducted response in microvasculature. For this reason, deletion or mutation of

336-536: The existence of communication between adherens junctions and gap junctions, suggesting a higher level of coordination than previously thought. Connexin gap junctions are found only in vertebrates , while a functionally analogous (but genetically unrelated) group of proteins, the innexins , are responsible for gap junctions in invertebrate species. Innexin orthologs have also been identified in Chordates , but they are no longer capable of forming gap junctions. Instead,

357-437: The maturation of certain cochlear cells, both of which are critical for the process of converting sound waves into electrical nerve impulses. In the skin, GJB2 contributes to the growth, maturation, and stability of the epidermis. Defects in this gene lead to the most common form of congenital deafness in developed countries, called DFNB1 (also known as connexin 26 deafness or GJB2 -related deafness). One fairly common mutation

378-399: The nucleotide and amino acid levels. For example, CX43 ( GJA1 ) is designated alpha-1 gap junction protein, whereas GJB1 (CX32), and GJB2 (CX26; this protein) are called beta-1 and beta-2 gap junction proteins, respectively. This nomenclature emphasizes that GJB1 and GJB2 are more homologous to each other than either of them is to gap junction protein, alpha GJA1. Gap junction beta-2 protein

399-477: The same name This set index article includes a list of related items that share the same name (or similar names). If an internal link incorrectly 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=Gap_junction_protein&oldid=1157965070 " Category : Set index articles Hidden categories: Articles with short description Short description

420-504: The various connexin isoforms produces distinctive phenotypes and pathologies. While mutations in Cx43 are mostly linked to oculodentodigital dysplasia, Cx47 mutations are associated with Pelizaeus-Merzbacher -like disease and lymphedema. Cx40 mutations are principally linked to atrial fibrillation. Mutations in Cx37 have not yet been described, but polymorphisms in the Cx37 gene have been implicated in

441-644: The visual function for various lighting conditions. Cell coupling is governed by several mechanisms, including connexin expression. Decrock et al. . have discussed a multilevel platform via which connexins and pannexins can influence the following cellular functions within a tissue: (1) connexin gap junctional channels (GJCs) enable direct cell-cell communication of small molecules, (2) connexin hemichannels and pannexin channels can contribute to autocrine / paracrine signaling pathways, and (3) different structural domains of these proteins allow for channel-independent functions, such as cell-cell adhesion , interactions with

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