Summary: Kv2 voltage-gated K+ channel
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Voltage-gated potassium channel Edit Wikipedia article
|Ion channel (eukaryotic)|
Potassium channel, structure in a membrane-like environment. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue dots.
|Ion channel (bacterial)|
Potassium channel KcsA. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue dots.
|Slow voltage-gated potassium channel (Potassium channel, voltage-dependent, beta subunit, KCNE)|
|KCNQ voltage-gated potassium channe|
|Kv2 voltage-gated K+ channel|
Voltage-gated potassium channels are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized cell to a resting state.
 Alpha subunits
Alpha subunits form the actual conductance pore. Based on sequence homology of the hydrophobic transmembrane cores, the alpha subunits of voltage-gated potassium channels are grouped into 12 classes. These are labeled Kvα1-12. The following is a list of the 40 known human voltage-gated potassium channel alpha subunits grouped first according to function and then subgrouped according to the Kv sequence homology classification scheme:
 Delayed rectifier
slowly inactivating or non-inactivating
- Kvα1.x - Shaker-related: Kv1.1 (KCNA1), Kv1.2 (KCNA2), Kv1.3 (KCNA3), Kv1.5 (KCNA5), Kv1.6 (KCNA6), Kv1.7 (KCNA7), Kv1.8 (KCNA10)
- Kvα2.x - Shab-related: Kv2.1 (KCNB1), Kv2.2 (KCNB2)
- Kvα3.x - Shaw-related: Kv3.1 (KCNC1), Kv3.2 (KCNC2)
- Kvα7.x: Kv7.1 (KCNQ1) - KvLQT1, Kv7.2 (KCNQ2), Kv7.3 (KCNQ3), Kv7.4 (KCNQ4), Kv7.5 (KCNQ5)
- Kvα10.x: Kv10.1 (KCNH1)
 A-type potassium channel
- Kvα1.x - Shaker-related: Kv1.4 (KCNA4)
- Kvα3.x - Shaw-related: Kv3.3 (KCNC3), Kv3.4 (KCNC4)
- Kvα4.x - Shal-related: Kv4.1 (KCND1), Kv4.2 (KCND2), Kv4.3 (KCND3)
- Kvα10.x: Kv10.2 (KCNH5)
Passes current more easily into the inwards direction (Into the cell).
 Slowly activating
Unable to form functional channels as homotetramers but instead heterotetramerize with Kvα2 family members to form conductive channels.
- Kvα5.x: Kv5.1 (KCNF1)
- Kvα6.x: Kv6.1 (KCNG1), Kv6.2 (KCNG2), Kv6.3 (KCNG3), Kv6.4 (KCNG4)
- Kvα8.x: Kv8.1 (KCNV1), Kv8.2 (KCNV2)
- Kvα9.x: Kv9.1 (KCNS1), Kv9.2 (KCNS2), Kv9.3 (KCNS3)
 Beta subunits
Beta subunits are auxiliary proteins that associate with alpha subunits, sometimes in a α4β4 stoichiometry. These subunits do not conduct current on their own but rather modulate the activity of Kv channels.
- Kvβ1 (KCNAB1)
- Kvβ2 (KCNAB2)
- Kvβ3 (KCNAB3)
- minK (KCNE1)
- MiRP1 (KCNE2)
- MiRP2 (KCNE3)
- MiRP3 (KCNE4)
- KCNE1-like (KCNE1L)
- KCNIP1 (KCNIP1)
- KCNIP2 (KCNIP2)
- KCNIP3 (KCNIP3)
- KCNIP4 (KCNIP4)
Proteins minK and MiRP1 are putative hERG beta subunits.
 Animal research
The voltage-gated K+ channels that provide the outward currents of action potentials have similarities to bacterial K+ channels.
These channels have been studied by X-ray diffraction, allowing determination of structural features at atomic resolution.
The function of these channels is explored by electrophysiological studies.
Genetic approaches include screening for behavioral changes in animals with mutations in K+ channel genes. Such genetic methods allowed the genetic identification of the "Shaker" K+ channel gene in Drosophila before ion channel gene sequences were well known.
Study of the altered properties of voltage-gated K+ channel proteins produced by mutated genes has helped reveal the functional roles of K+ channel protein domains and even individual amino acids within their structures.
Typically, vertebrate voltage-gated K+ channels are tetramers of four identical subunits arranged as a ring, each contributing to the wall of the trans-membrane K+ pore. Each subunit is composed of six membrane spanning hydrophobic α-helical sequences. The high resolution crystallographic structure of the rat Kvα1.2/β2 channel has recently been solved (Protein Databank Accession Number ), and then refined in a lipid membrane-like environment (PDB 2r9r).
Voltage-gated K+ channels are selective for K+ over other cations such as Na+. There is a selectivity filter at the narrowest part of the transmembrane pore.
Channel mutation studies have revealed the parts of the subunits that are essential for ion selectivity. They include the amino acid sequence (Thr-Val-Gly-Tyr-Gly) or (Thr-Val-Gly-Phe-Gly) typical to the selectivity filter of voltage-gated K+ channels. As K+ passes through the pore, interactions between potassium ions and water molecules are prevented and the K+ interacts with specific atomic components of the Thr-Val-Gly-X-Gly sequences from the four channel subunits.
It seems illogical at first that a channel should be able to allow potassium ions but not the smaller sodium ions through. However in an aqueous environment, potassium and sodium cations are solvated by water molecules. When moving through the selectivity filter of the potassium channel, the water-K+ interactions are replaced by interactions between K+ and carbonyl groups of the channel protein. The diameter of the selectivity filter is ideal for the potassium cation, but too big for the smaller sodium cation. Hence the potassium cations are well "solvated" by the protein carbonyl groups, but these same carbonyl groups are too far apart to adequately solvate the sodium cation. Hence, the passage of potassium cations through this selectivity filter is strongly favored over sodium cations.
 Open and closed conformations
Attempts continue to relate the structure of the mammalian voltage-gated K+ channel to its ability to respond to the voltage that exists across the membrane. Specific domains of the channel subunits have been identified that are important for voltage-sensing and converting between the open conformation of the channel and closed conformations. There are at least two closed conformations; in one, the channel can open if the membrane potential becomes positive inside. Voltage-gated K+ channels inactivate after opening, entering a distinctive, second closed conformation. In the inactivated conformation, the channel cannot open, even if the transmembrane voltage is favorable. The amino terminal domain of the K+ channel or an auxiliary protein can mediate "N-type" inactivation. The former has been described as a "ball and chain" model, where the N-terminus of the protein forms a ball that is tethered to the rest of the protein through a loop (the chain). The tethered ball is transiently sucked into the inner porehole, preventing ion movement through the channel.
 See also
- Gutman GA, Chandy KG, Grissmer S, Lazdunski M, McKinnon D, Pardo LA, Robertson GA, Rudy B, Sanguinetti MC, Stuhmer W, Wang X (2005). "International Union of Pharmacology. LIII. Nomenclature and molecular relationships of voltage-gated potassium channels.". Pharmacol Rev 57 (4): 473–508. doi:10.1124/pr.57.4.10. PMID 16382104.
- Pongs O, Leicher T, Berger M, Roeper J, Bahring R, Wray D, Giese KP, Silva AJ, Storm JF (1999). "Functional and molecular aspects of voltage-gated K+ channel beta subunits". Ann N Y Acad Sci 868 (Apr 30): 344–55. doi:10.1111/j.1749-6632.1999.tb11296.x. PMID 10414304.
- Li Y, Um SY, McDonald TV (2006). "Voltage-gated potassium channels: regulation by accessory subunits". Neuroscientist 12 (3): 199–210. doi:10.1177/1073858406287717. PMID 16684966.
- Zhang M, Jiang M, Tseng GN (2001). "minK-related peptide 1 associates with Kv4.2 and modulates its gating function: potential role as beta subunit of cardiac transient outward channel?". Circ Res 88 (10): 1012–9. doi:10.1161/hh1001.090839. PMID 11375270.
- McCrossan ZA, Abbott GW (2004). "The MinK-related peptides". Neuropharmacology 47 (6): 787–821. doi:10.1016/j.neuropharm.2004.06.018. PMID 15527815.
- Anantharam A, Abbott GW (2005). "Does hERG coassemble with a beta subunit? Evidence for roles of MinK and MiRP1". Novartis Found Symp 266 (42): 112–7, 155–8. doi:10.1002/047002142X.fmatter. PMID 16050264.
- Long SB, Campbell EB, Mackinnon R (2005). "Crystal structure of a mammalian voltage-dependent Shaker family K+ channel". Science 309 (5736): 897–903. doi:10.1126/science.1116269. PMID 16002581.
- Lee S, Lee A, Chen J, MacKinnon R (2005). "Structure of the KvAP voltage-dependent K+ channel and its dependence on the lipid membrane.". Proc Natl Acad Sci USA 102 (43): 15441–6. doi:10.1073/pnas.0507651102. PMC 1253646. PMID 16223877.
- Armstrong CM, Bezanilla F (April 1973). "Currents related to movement of the gating particles of the sodium channels". Nature 242 (5398): 459–61. doi:10.1038/242459a0. PMID 4700900.
- Murrell-Lagnado RD, Aldrich RW (December 1993). "Energetics of Shaker K channels block by inactivation peptides". J. Gen. Physiol. 102 (6): 977–1003. doi:10.1085/jgp.102.6.977. PMC 2229186. PMID 8133246.
- Voltage-Gated Potassium Channels at the US National Library of Medicine Medical Subject Headings (MeSH)
- "Voltage-Gated Potassium Channels". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology.
- Li B, Gallin W (2004). "VKCDB: voltage-gated potassium channel database.". BMC Bioinformatics 5: 3. doi:10.1186/1471-2105-5-3. PMC 317694. PMID 14715090.
- "Voltage-gated potassium channel database (VKCDB)" at ualberta.ca
- UMich Orientation of Proteins in Membranes families/superfamily-8 - Spatial positions of voltage gated potassium channels in membranes
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Kv2 voltage-gated K+ channel Provide feedback
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This tab holds annotation information from the InterPro database.
InterPro entry IPR003973
Potassium channels are the most diverse group of the ion channel family [PUBMED:1772658, PUBMED:1879548]. They are important in shaping the action potential, and in neuronal excitability and plasticity [PUBMED:2451788]. The potassium channel family is composed of several functionally distinct isoforms, which can be broadly separated into 2 groups [PUBMED:2555158]: the practically non-inactivating 'delayed' group and the rapidly inactivating 'transient' group.
These are all highly similar proteins, with only small amino acid changes causing the diversity of the voltage-dependent gating mechanism, channel conductance and toxin binding properties. Each type of K+ channel is activated by different signals and conditions depending on their type of regulation: some open in response to depolarisation of the plasma membrane; others in response to hyperpolarisation or an increase in intracellular calcium concentration; some can be regulated by binding of a transmitter, together with intracellular kinases; while others are regulated by GTP-binding proteins or other second messengers [PUBMED:2448635]. In eukaryotic cells, K+ channels are involved in neural signalling and generation of the cardiac rhythm, act as effectors in signal transduction pathways involving G protein-coupled receptors (GPCRs) and may have a role in target cell lysis by cytotoxic T-lymphocytes [PUBMED:1373731]. In prokaryotic cells, they play a role in the maintenance of ionic homeostasis [PUBMED:11178249].
All K+ channels discovered so far possess a core of alpha subunits, each comprising either one or two copies of a highly conserved pore loop domain (P-domain). The P-domain contains the sequence (T/SxxTxGxG), which has been termed the K+ selectivity sequence. In families that contain one P-domain, four subunits assemble to form a selective pathway for K+ across the membrane. However, it remains unclear how the 2 P-domain subunits assemble to form a selective pore. The functional diversity of these families can arise through homo- or hetero-associations of alpha subunits or association with auxiliary cytoplasmic beta subunits. K+ channel subunits containing one pore domain can be assigned into one of two superfamilies: those that possess six transmembrane (TM) domains and those that possess only two TM domains. The six TM domain superfamily can be further subdivided into conserved gene families: the voltage-gated (Kv) channels; the KCNQ channels (originally known as KvLQT channels); the EAG-like K+ channels; and three types of calcium (Ca)-activated K+ channels (BK, IK and SK) [PUBMED:11178249]. The 2TM domain family comprises inward-rectifying K+ channels. In addition, there are K+ channel alpha-subunits that possess two P-domains. These are usually highly regulated K+ selective leak channels.
The Kv family can be divided into several subfamilies on the basis of sequence similarity and function. Four of these subfamilies, Kv1 (Shaker), Kv2 (Shab), Kv3 (Shaw) and Kv4 (Shal), consist of pore-forming alpha subunits that associate with different types of beta subunit. Each alpha subunit comprises six hydrophobic TM domains with a P-domain between the fifth and sixth, which partially resides in the membrane. The fourth TM domain has positively charged residues at every third residue and acts as a voltage sensor, which triggers the conformational change that opens the channel pore in response to a displacement in membrane potential [PUBMED:10712896]. More recently, 4 new electrically-silent alpha subunits have been cloned: Kv5 (KCNF), Kv6 (KCNG), Kv8 and Kv9 (KCNS). These subunits do not themselves possess any functional activity, but appear to form heteromeric channels with Kv2 subunits, and thus modulate Shab channel activity [PUBMED:9305895]. When highly expressed, they inhibit channel activity, but at lower levels show more specific modulatory actions.
The Kv2 voltage-dependent potassium channels (also known as the Shab family) are responsible for much of the delayed rectifier current in Drosophila melanogaster (Fruit fly) nervous system and muscle. However, in vertebrates, Kv2 channels have been shwon to be involved in the delayed rectifier currents of the heart and skeletal muscles. They are also thought to be important in determining intrinsic neuronal excitability in both mammals and non-mammals [PUBMED:15950285]. Kv2 channels can be further divided into 2 subtypes, designated Kv2.1 and Kv2.2.
This entry represents the voltage-dependent Kv2 potassium channels.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||voltage-gated potassium channel complex (GO:0008076)|
|Molecular function||voltage-gated potassium channel activity (GO:0005249)|
|Biological process||potassium ion transport (GO:0006813)|
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|Number in full:||108|
|Average length of the domain:||204.20 aa|
|Average identity of full alignment:||45 %|
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