Ion channels: Difference between revisions

[[Image:1qrq1.png|left|200px|thumb|Crystal structure of voltage-dependent potassium channel, [[1qrq]]]]

{{STRUCTURE_1qrq|  PDB=1qrq  | SIZE=300| SCENE=Ion_channels/Cv/1 |right|CAPTION=voltage-dependent potassium channel, [[1qrq]] }}

[[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 [[sodium channels]], or the [[chloride channels]]. Some, like the [[TRP channels]], let through various 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). [[Potassium Channel|Potassium channels]] (KCh) are subdivided to voltage-gated KCh and calcium-dependent KCh.  The latter are subdivided into high- (BK, LKCa), intermediate- and small-conductance KCh (human SK1, rat SK2, SKCa).

MthK is a calcium-dependent potassium channel from ''Methanobacterium thermoautrophicum''. MscL and MscS are large- and small-conductance mechanosensitive channels which protect bacteria from osmotic shock by allowing ions to flow across the cell membrane. Voltage-Dependent Calcium Channels (VDCC) allow Ca⁺⁺ to enter the cell resulting in muscle contraction, neuron excitation or hormone release.  VDCC are composed of several subunits and are named as a ''Cav'' gene product. Finally, ion channels are the fastest of all membrane transporters, with 10⁶ to 10⁸ transported units per second versus 10² to 10⁴ molecules per second for porters/carriers, or 10⁰ to 10³ for ATP-driven pumps. The images at the left and at the right correspond to one representative ion channel structure, ''i.e.'' the crystal structure of voltage-dependent potassium channel from ''Rattus norvegicus'' ([[1qrq]]).

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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]] and the [[pore-forming toxins]], as well as from non-ribosomally synthesized channels like [[gramicidin]], [[polyglutamine]] or [[digitoxin]]. All these proteins are '''passive''' transport proteins.

== Available 3D structures ==

 

See: [[Potassium_Channel#Additional_Structures_of_Potassium_Channels|Potassium Channels]]

 

 

 

 

 

 

 

 

 

 

 

 

[[2oau]], [[2vv5]] - EcMscS

 

 

[[2ahe]], [[2d2z]] – hClCh protein 4<br />