Innexin
Encyclopedia
An innexin is a member of a class of protein
s which is used to create gap junction
s in invertebrates. The innexin protein and its vertebrate homologue pannexin
1 have 4 transmembrane spanning units and, like the vertebrate connexin
gap junction protein, 6 innexin (or pannexin 1) subunits together form a channel, an "innexon," in the plasma membrane. Two innexons in apposed plasma membranes can form a gap junction.
The pannexin family combines invertebrate gap junction proteins and their vertebrate homologs. These proteins have been named innexins. Gap junctions are composed of membrane proteins, which form a channel permeable for ions and small molecules connecting cytoplasm of adjacent cells. Although gap junctions provide similar functions in all multicellular organisms, until recently it was believed that vertebrates and invertebrates use unrelated proteins for this purpose. While the connexins family of gap junction proteins is well- characterised in vertebrates, no homologs have been found in invertebrates. In turn, gap junction molecules with no sequence homology to connexins have been identified in insects and nematodes. It has been suggested that these proteins are specific invertebrate gap junctions, and they were thus named innexins (invertebrate analog of connexins). As innexin homologs were recently identified in other taxonomic groups including vertebrates, indicating their ubiquitous distribution in the animal kingdom, they were called pannexins (from the Latin pan-all, throughout, and nexus-connection, bond).
Genomes of vertebrates carry probably a conserved set of 3 pannexin paralogs (PANX1, PANX2 and PANX3). Invertebrate genomes may contain more than a dozen pannexin (innexin) genes. Vinnexins, viral homologs of pannexins/innexins, were identified in Polydnaviruses that occur in obligate symbiotic associations with parasitoid wasps. It was suggested that virally encoded vinnexin proteins may function to alter gap junction proteins in infected host cells, possibly modifying cell-cell communication during encapsulation responses in parasitized insects. Structurally pannexins are simillar to connexins. Both types of protein consist of a cytoplasmic N-terminal domain, followed by four transmembrane segments that delimit two extracellular and one cytoplasmic loops; the C- terminal domain is cytoplasmic.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s which is used to create gap junction
Gap junction
A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....
s in invertebrates. The innexin protein and its vertebrate homologue pannexin
Pannexin
Pannexins are a family of vertebrate proteins identified by their homology to the invertebrate innexins...
1 have 4 transmembrane spanning units and, like the vertebrate connexin
Connexin
Connexins, or gap junction proteins, are a family of structurally-related transmembrane proteins that assemble to form vertebrate gap junctions . Each gap junction is composed of two hemichannels, or connexons, which are themselves each constructed out of six connexin molecules...
gap junction protein, 6 innexin (or pannexin 1) subunits together form a channel, an "innexon," in the plasma membrane. Two innexons in apposed plasma membranes can form a gap junction.
The pannexin family combines invertebrate gap junction proteins and their vertebrate homologs. These proteins have been named innexins. Gap junctions are composed of membrane proteins, which form a channel permeable for ions and small molecules connecting cytoplasm of adjacent cells. Although gap junctions provide similar functions in all multicellular organisms, until recently it was believed that vertebrates and invertebrates use unrelated proteins for this purpose. While the connexins family of gap junction proteins is well- characterised in vertebrates, no homologs have been found in invertebrates. In turn, gap junction molecules with no sequence homology to connexins have been identified in insects and nematodes. It has been suggested that these proteins are specific invertebrate gap junctions, and they were thus named innexins (invertebrate analog of connexins). As innexin homologs were recently identified in other taxonomic groups including vertebrates, indicating their ubiquitous distribution in the animal kingdom, they were called pannexins (from the Latin pan-all, throughout, and nexus-connection, bond).
Genomes of vertebrates carry probably a conserved set of 3 pannexin paralogs (PANX1, PANX2 and PANX3). Invertebrate genomes may contain more than a dozen pannexin (innexin) genes. Vinnexins, viral homologs of pannexins/innexins, were identified in Polydnaviruses that occur in obligate symbiotic associations with parasitoid wasps. It was suggested that virally encoded vinnexin proteins may function to alter gap junction proteins in infected host cells, possibly modifying cell-cell communication during encapsulation responses in parasitized insects. Structurally pannexins are simillar to connexins. Both types of protein consist of a cytoplasmic N-terminal domain, followed by four transmembrane segments that delimit two extracellular and one cytoplasmic loops; the C- terminal domain is cytoplasmic.
Examples
Examples include:- C. elegansCaenorhabditis elegansCaenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
- Unc-7
- Unc-9
- DrosophilaDrosophila melanogasterDrosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
- Ogre
- shaking-B
- Hirudo medicinalis
- Hm-inx1
- Hm-inx2
- Hm-inx3
- Hm-inx6