Summary: KCNQ voltage-gated potassium 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.
- 1 Classification
- 2 Animal research
- 3 Structure
- 4 Selectivity
- 5 Open and closed conformations
- 6 See also
- 7 References
- 8 External links
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:
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 in the inward direction (into the cell, from outside).
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 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.
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-[YF]-Gly sequences from the four channel subunits.
It may seem counterintuitive that a channel should 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
The structure of the mammalian voltage-gated K+ channel has been used to explain its ability to respond to the voltage across the membrane. Specific domains of the channel subunits have been identified that are responsible for voltage-sensing and converting between the open and closed conformations of the channel. There are at least two closed conformations. In the first, the channel can open if the membrane potential becomes more positive. This type of gating is mediated by a voltage-sensing domain that consists of the S4 alpha helix that contains 6–7 positive charges. Changes in membrane potential cause this alpha helix to move in the lipid bilayer. This movement in turn results a conformational change in the adjacent S5–S6 helices that form the channel pore and cause this pore to open or close. In the second, "N-type" inactivation, voltage-gated K+ channels inactivate after opening, entering a distinctive, closed conformation. In this 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 mechanism of this type of inactivation 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 blocks the inner porehole, preventing ion movement through the channel.
- 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.
- Antz C, Fakler B (August 1998). "Fast Inactivation of Voltage-Gated K(+) Channels: From Cartoon to Structure". News Physiol. Sci. 13 (4): 177–182. PMID 11390785.
- 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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KCNQ voltage-gated potassium channel Provide feedback
This family matches to the C-terminal tail of KCNQ type potassium channels.
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This tab holds annotation information from the InterPro database.
InterPro entry IPR013821
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.
KCNQ channels (also known as KQT-like channels) differ from other voltage-gated 6 TM helix channels, chiefly in that they possess no tetramerisation domain. Consequently, they rely on interaction with accessory subunits, or form heterotetramers with other members of the family [PUBMED:10838601]. Currently, 5 members of the KCNQ family are known. These have been found to be widely distributed within the body, having been shown to be expressed in the heart, brain, pancreas, lung, placenta and ear. They were initially cloned as a result of a search for proteins involved in cardiac arhythmia. Subsequently, mutations in other KCNQ family members have been shown to be responsible for some forms of hereditary deafness [PUBMED:8528244] and benign familial neonatal epilepsy [PUBMED:9430594].
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Curation and family details
|Number in seed:||9|
|Number in full:||568|
|Average length of the domain:||163.00 aa|
|Average identity of full alignment:||42 %|
|Average coverage of the sequence by the domain:||29.81 %|
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build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||9|
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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the KCNQ_channel domain has been found. There are 9 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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