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Ion channel
Bla Bla voltage-gated ion channel
Identifiers
SymbolIon_trans
PfamPF00520
InterProIPR005821
SCOP21bl8 / SCOPe / SUPFAM
TCDB1.A.1
OPM superfamily8
OPM protein2a79
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
PDB1qg9A:157-176 2a79B:225-409 1ho7A:378-397 1ho2A:378-397 1ujlA:570-611
Ion channel (bacterial)
Voltage-gated channel ....
Identifiers
SymbolIon_trans_2
PfamPF07885
InterProIPR013099
SCOP21bl8 / SCOPe / SUPFAM
OPM protein1r3j
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
PDB1lnqE:25-100 2a0lB:169-250 1orqC:169-250

1k4cC:34-116 1r3iC:34-116 2bocC:34-116 1j95C:34-116 1r3lC:34-116 1jvmB:34-116 1bl8C:34-116 2a9hD:34-116 1k4dC:34-116 1r3jC:34-116 1r3kC:34-116 2bobC:34-116

1p7bB:77-151
Slow voltage-gated potassium channel (Potassium channel, voltage-dependent, beta subunit, KCNE)
Identifiers
SymbolISK_Channel
PfamPF02060
InterProIPR000369
TCDB8.A.10
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
KCNQ voltage-gated potassium channe
Identifiers
SymbolKCNQ_channel
PfamPF03520
InterProIPR013821
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
Kv2 voltage-gated K+ channel
Identifiers
SymbolKv2channel
PfamPF03521
InterProIPR003973
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

TEST

Voltage-gated ion channel

Voltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical membrane potential near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells.

They have a crucial role in excitable neuronal and muscle tissues, allowing a rapid and co-ordinated depolarization in response to triggering voltage change. Found along the axon and at the synapse, voltage-gated ion channels directionally propagate electrical signals.

Structure

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They generally are composed of several subunits arranged in such a way that there is a central pore through which ions can travel down their electrochemical gradients. The channels tend to be ion-specific, although similarly sized and charged ions may sometimes travel through them.

Examples include:

Mechanism

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From crystallographic structural studies of a potassium channel, assuming that this structure remains intact in the corresponding plasma membrane, it is possible to surmise that when a potential difference is introduced over the membrane, the associated electromagnetic field induces a conformational change in the potassium channel. The conformational change distorts the shape of the channel proteins sufficiently such that the cavity, or channel, opens to admit ion influx or efflux to occur across the membrane, down its electrochemical gradient. This subsequently generates an electrical current sufficient to depolarise the cell membrane.

Voltage-gated sodium channels and calcium channels are made up of a single polypeptide with four homologous domains. Each domain contains 6 membrane spanning alpha helices. One of these helices, S4, is the voltage sensing helix.[1] It has many positive charges such that a high positive charge outside the cell repels the helix, keeping the channel in its closed state. Depolarization of the cell interior causes the helix to move, inducing a conformational change such that ions may flow through the channel (the open state). Potassium channels function in a similar way, with the exception that they are composed of four separate polypeptide chains, each comprising one domain.

The voltage-sensitive protein domain of these channels (the "voltage sensor") generally contains a region composed of S3b and S4 helices, known as the "paddle" due to its shape, which appears to be a conserved sequence, interchangeable across a wide variety of cells and species. A similar voltage sensor paddle has also been found in a family of voltage sensitive phosphatases in various species.[2] Genetic engineering of the paddle region from a species of volcano-dwelling archaebacteria into rat brain potassium channels results in a fully functional ion channel, as long as the whole intact paddle is replaced.[3] This "modularity" allows use of simple and inexpensive model systems to study the function of this region, its role in disease, and pharmaceutical control of its behavior rather than being limited to poorly characterized, expensive, and/or difficult to study preparations.[4]

References

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  1. ^ Voltage sensor in the voltage gated sodium and potassium channels | PharmaXChange.info
  2. ^ Murata, Y.; Iwasaki, H.; Sasaki, M.; Inaba, K.; Okamura, Y. (2005). "Phosphoinositide phosphatase activity coupled to an intrinsic voltage sensor". Nature. 435 (7046): 1239–1243. doi:10.1038/nature03650. PMID 15902207.
  3. ^ Alabi AA, Bahamonde MI, Jung HJ, Kim JI, Swartz KJ (November 2007). "Portability of paddle motif function and pharmacology in voltage sensors". Nature. 450 (7168): 370–5. doi:10.1038/nature06266. PMC 2709416. PMID 18004375.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ Long SB, Tao X, Campbell EB, MacKinnon R (November 2007). "Atomic structure of a voltage-dependent K+ channel in a lipid membrane-like environment". Nature. 450 (7168): 376–82. doi:10.1038/nature06265. PMID 18004376.{{cite journal}}: CS1 maint: multiple names: authors list (link)

See also

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Category:Ion channels Category:Electrophysiology Category:Integral membrane proteins