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Innexin

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Innexin
Identifiers
SymbolInnexin
PfamPF00876
InterProIPR000990
TCDB1.A.25
OPM superfamily194
OPM protein5h1r
Available protein structures:
Pfam structures/ECOD
PDBRCSB PDB;PDBe;PDBj
PDBsumstructure summary

Innexinsaretransmembrane proteinsthat formgap junctionsininvertebrates.Gap junctions are composed ofmembrane proteinsthat form achannelpermeable to ions and small molecules connecting thecytoplasmof adjacent cells. Although gap junctions provide similar functions in all multicellular organisms, it was not known what proteins invertebrates used for this purpose until the late 1990s. While theconnexinfamily of gap junction proteins was well-characterized invertebrates,no homologues were found innon-chordates.

Innexins or related proteins are widespread amongEumetazoa,with the exception ofechinoderms.[1]

Discovery[edit]

Gap junction proteins with nosequence homologyto connexins were initially identified infruit flies.It was suggested that these proteins are specific invertebrate gap junctions, and they were thus named "innexins" (invertebrate analog of connexins).[2]They were later identified in diverse invertebrates. Invertebrate genomes may contain more than a dozen innexin genes. Once the human genome was sequenced, innexin homologues were identified in humans and then in other vertebrates, indicating their ubiquitous distribution in the animal kingdom. These homologues were called "pannexins"(from the Greekpan- all, throughout, and Latinnexus- connection, bond).[3][4]However, increasing evidence suggests that pannexins do not form gap junctions unless overexpressed in tissue and thus, differ functionally from innexins.[5]

Structure[edit]

Innexins have fourtransmembrane segments(TMSs) and, like the vertebrateconnexingap junction protein, innexin subunits together form a channel (an "innexon" ) in theplasma membraneof the cell.[6]Two innexons in apposed plasma membranes can form a gap junction. Innexons are made from eight subunits, instead of the six subunits of connexons.[7]Structurally, innexins and connexins are very similar, consisting of 4 transmembrane domains, 2 extracellular and 1 intracellular loop, along with intracellular N- and C-terminal tails. Despite this shared topology, the protein families do not share enough sequence similarity to confidently infer common ancestry.

Pannexins are similar to innexins and are usually considered a sub-group, but they do not participate in the formation of gap junctions and the channels have seven subunits.[8][9]

Vinnexins,viral homologues of innexins, were identified inpolydnavirusesthat occur in obligate symbiotic associations with parasitoid wasps. It was suggested that vinnexins may function to alter gap junction proteins in infected host cells, possibly modifying cell-cell communication during encapsulation responses in parasitized insects.[10][11][12]

Function[edit]

Innexins form gap junctions found in invertebrates. They also form non-junctional membrane channels with properties similar to those of pannexons.[13]N-terminal- elongated innexins can act as a plug to manipulate hemichannel closure and provide a mechanism connecting the effect of hemichannel closure directly toapoptoticsignal transductionfrom the intracellular to the extracellular compartment.[14]

The vertebrate homolog pannexin do not form gap junctions. They only form the hemichannel "pannexons". These hemichannels can be present in plasma, ER and Golgi membranes. They transport Ca2+,ATP,inositol triphosphateand other small molecules and can form hemichannels with greater ease than connexin subunits.[15]

Transport reaction[edit]

The transport reactions catalyzed by innexin gap junctions is:

Small molecules (cell 1 cytoplasm) ⇌ small molecules (cell 2 cytoplasm)

Or for hemichannels:

Small molecules (cell cytoplasm) ⇌ small molecules (out)

Examples[edit]

See also[edit]

References[edit]

  1. ^Hasegawa DK, Turnbull MW (April 2014). "Recent findings in evolution and function of insect innexins".FEBS Letters.588(8): 1403–10.doi:10.1016/j.febslet.2014.03.006.PMID24631533.S2CID25970503.
  2. ^Phelan P, Stebbings LA, Baines RA, Bacon JP, Davies JA, Ford C (January 1998). "Drosophila Shaking-B protein forms gap junctions in paired Xenopus oocytes".Nature.391(6663): 181–4.Bibcode:1998Natur.391..181P.doi:10.1038/34426.PMID9428764.S2CID205003383.
  3. ^Panchin Y, Kelmanson I, Matz M, Lukyanov K, Usman N, Lukyanov S (June 2000)."A ubiquitous family of putative gap junction molecules".Current Biology.10(13): R473-4.doi:10.1016/S0960-9822(00)00576-5.PMID10898987.S2CID20001454.
  4. ^Kelmanson IV, Shagin DA, Usman N, Matz MV, Lukyanov SA, Panchin YV (December 2002). "Altering electrical connections in the nervous system of the pteropod mollusc Clione limacina by neuronal injections of gap junction mRNA".The European Journal of Neuroscience.16(12): 2475–6.doi:10.1046/j.1460-9568.2002.02423.x.PMID12492443.S2CID41324492.
  5. ^Dahl G. & Harris A. 2009. Pannexins or Connexins? Chapter 12. In: A. Harris, D. Locke (eds.), Connexins: A Guidedoi:10.1007/978-1-59745-489-6_12
  6. ^Bao L, Samuels S, Locovei S, Macagno ER, Muller KJ, Dahl G (December 2007)."Innexins form two types of channels".FEBS Letters.581(29): 5703–8.doi:10.1016/j.febslet.2007.11.030.PMC2489203.PMID18035059.
  7. ^Oshima A, Matsuzawa T, Murata K, Tani K, Fujiyoshi Y (March 2016)."Hexadecameric structure of an invertebrate gap junction channel".Journal of Molecular Biology.428(6): 1227–1236.doi:10.1016/j.jmb.2016.02.011.PMID26883891.
  8. ^Michalski K, Syrjanen JL, Henze E, Kumpf J, Furukawa H, Kawate T (February 2020)."The cryo-EM structure of a pannexin 1 reveals unique motifs for ion selection and inhibition".eLife.9:e54670.doi:10.7554/eLife.54670.PMC7108861.PMID32048993.
  9. ^Qu R, Dong L, Zhang J, Yu X, Wang L, Zhu S (March 2020)."Cryo-EM structure of human heptameric Pannexin 1 channel".Cell Research.30(5): 446–448.doi:10.1038/s41422-020-0298-5.PMC7196123.PMID32203128.
  10. ^Turnbull M, Webb B (2002).Perspectives on polydnavirus origins and evolution.Advances in Virus Research. Vol. 58. pp. 203–54.doi:10.1016/S0065-3527(02)58006-4.ISBN9780120398584.PMID12205780.
  11. ^Kroemer JA, Webb BA (2004). "Polydnavirus genes and genomes: emerging gene families and new insights into polydnavirus replication".Annual Review of Entomology.49(1): 431–56.doi:10.1146/annurev.ento.49.072103.120132.PMID14651471.
  12. ^Marziano N.K.; Hasegawa D.K.; Phelan P.; Turnbull M.W. (October 2011)."Functional Interactions between Polydnavirus and Host Cellular Innexins".Journal of Virology.85(19): 10222–9.doi:10.1128/jvi.00691-11.PMC3196458.PMID21813607.
  13. ^Bao L, Samuels S, Locovei S, Macagno ER, Muller KJ, Dahl G (December 2007)."Innexins form two types of channels".FEBS Letters.581(29): 5703–8.doi:10.1016/j.febslet.2007.11.030.PMC2489203.PMID18035059.
  14. ^Chen YB, Xiao W, Li M, Zhang Y, Yang Y, Hu JS, Luo KJ (May 2016). "N-TERMINALLY ELONGATED SpliInx2 AND SpliInx3 REDUCE BACULOVIRUS-TRIGGERED APOPTOSIS VIA HEMICHANNEL CLOSURE".Archives of Insect Biochemistry and Physiology.92(1): 24–37.doi:10.1002/arch.21328.PMID27030553.
  15. ^Shestopalov VI, Panchin Y (February 2008)."Pannexins and gap junction protein diversity".Cellular and Molecular Life Sciences.65(3): 376–94.doi:10.1007/s00018-007-7200-1.PMC11131650.PMID17982731.S2CID23181471.

Further reading[edit]

External links[edit]

This article incorporates text from the public domainPfamandInterPro:IPR000990

As ofthis edit,this article uses content from"1.A.25 The Gap Junction-forming Innexin (Innexin) Family",which is licensed in a way that permits reuse under theCreative Commons Attribution-ShareAlike 3.0 Unported License,but not under theGFDL.All relevant terms must be followed.

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