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| '''Ion channels''' are membrane proteins that catalyze the passive transport of ions through the cell membrane. Most ion channels are specific to an ion, like the [[natrium channels]], or the [[chloride channels]]. Some, like the [[TRP channels]], let through a bunch of cations. Another property of ion channels is that they can be either driven by voltage or concentration gradients, or they can be gated (by voltage, ligands, touch and other sensory signal). Finally, ion channels are the fastest of all membrane transporters, with 10^6 to 10^8 transported units per second versus 10^2 to 10^4 molecules per second for porters/carriers, or 10^0 to 10^3 for ATP-driven pumps. | | <applet load='1xyz' /> |
| | | '''Test''' <ref>Ref</ref> |
| == Classification ==
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| TCDB, the most sophisticated classification of transport proteins to date, classify ion channels as a heterogenous subset of all '''α-type channels''', whose singular property is to consist mainly of [[alpha helix|α-helices]] that span the membrane. They are distinct in this from the [[beta-barrel porins]], the [[pore-forming toxins]], but also from non-ribosomally synthesized channels like [[gramicidin]], [[polyglutamine]] or [[digitoxin]]. All these proteins are '''passive''' transport proteins.
| | <references/> |
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| == Available structures ==
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| Membrane transport proteins are notoriously difficult to crystallize while in a working state. So, it's no surprise that there are preciously few structure data for ion channels. At the moment, the following α-type ion channels have been at least partly resolved:
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| * the [[voltage-dependent potassium channel]] K<sub>v</sub>1 from ''Rattus norvegicus'' ([[1qrq]], [[1exb]], [[1t1d]], [[2a79]], [[2r9r]], [[3eau]], [[3eb3]], [[3eb4]])
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| * the [[voltage-dependent calcium channel]] from ''Rattus norvegicus'' (L-type: [[1t0h]], [[1t0j]], [[1vyt]], [[1vyu]], [[1vyv]], [[2vay]], [[3bxk]], R-type: [[3bxl]])
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| * the [[voltage-gated potassium channel]] KcsA from ''Streptomyces lividans'' and ''Mus musculus'' with the structures [[1bl8]], [[1k4c]], [[1k4d]], [[2bob]], [[2boc]], [[2hg5]],[[2h8p]], [[2hfe]], [[2itc]], [[2itd]], [[2k1e]], [[2nlj]]
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| * the [[voltage-gated potassium channel]] K<sub>v</sub>AP from ''Aeropyrum pernix'' ([[1orq]], [[2a0l]]), and human K<sub>v</sub>7 ([[2ovc]], [[3bj4]])
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| * the [[voltage-gated sodium channel]] Na<sub>v</sub>1.2 ([[1byy]], [[2kav]]) and Na<sub>v</sub>1.5 ([[2kbi]])
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| * the [[calcium-gated potassium channel mthK]] from ''Methanobacterium thermoautotrophicum'' ([[1lnq]], [[2fy8]])
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| * the hyperpolarization-activated and cyclic nucleotide-gated K+ channel [[HCN]] from ''Mus musculus'' ([[1q3e]], [[1q43]], [[1q5o]], [[2ptm]], [[2q0a]], [[3bpz]])
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| * the [[inward rectifier potassium channels]] KirBac3.1 ([[1xl4]],[[1xl6]]) and Kir3.1 (Cyt. only: [[1n9p]], [[1u4e]], [[1u4f]], [[1p7b]], [[2e4f]])
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| * the acid-sensitive (proton-gated) cation channel [[ASIC]] from ''Gallus gallus'' ([[2qts]])
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| * the human [[intracellular chloride channel]] CLIC-2 ([[2per]], [[2r4v]], [[2r5g]])
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| * the [[nicotinic acetylcholine-activated cation-selective channel]] from ''Torpedo marmorata'' ([[1oed]], [[2bg9]], [[2k58]], [[2k59]])
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| * a [[potassium channel]] from ''Burkholderia pseudomallei'' ([[1p7b]])
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| * the [[ammonium transporter]] from ''Archaeoglobus fulgidus'' ([[2b2f]]) and from ''Nitrosomonas europaea'' ([[3b9y]], [[3b9z]], [[3bhs]])
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| * the small-conductance [[mechanosensitive channel]] from ''E. coli'' K12 ([[2oau]], [[2vv5]], see also [[2k2b]])
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| * [[TRP channels]] ([[2rfa]], [[3e7k]])
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| * human [[phospholamban]] ([[1zll]], [[2hyn]])
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| * the P7 [[viroporin]] of Hepatitis C virus ([[2k8j]])
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| * the [[M2 protein]] from Influenza A ([[1nyj]], [[2kad]], [[2rlf]], [[3c9j]])
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| Additionally the following non-ribosomally synthesized channel proteins constitute ion channels, and have their structure resolved:
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| * [[Gramicidin]] ([[1av2]], [[1c4d]], [[1mag]])
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| * fungal [[Antiamoebin]] ([[1joh]], [[1gq0]])
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| * fungal [[Trichotoxin]] ([[1m24]])
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| * further [[Peptaibol]] antibiotics ([[1ob4]], [[1ob6]], [[1ob7]])
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| We do not count ClC chloride carriers as ion channels, as they are secondary active [[carriers]].
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| == Weblinks ==
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| *[http://www.tcdb.org/ The TCDB database]
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| *[http://www.tcdb.org/tcdb/subclass2.php?tc=1.A TCDB: 1.A α-Type channels]
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| *[http://www.tcdb.org/pdb_structure.php TCDB: Transport proteins with PDB structures]
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