| Literature References | 1. KETCHUM, K.A., JOINER, W.J., SELLERS, A.J., KACZMAREK, L.K. AND
GOLDSTEIN, S.A.N.
A new family of outwardly rectifying potassium channel proteins with two
pore domains in tandem.
NATURE 376 690-695 (1995).
2. GOLDSTEIN, S.A.N., PRICE, L.A., ROSENTHAL, D.N. AND PAUSCH, M.H.
ORK1, a potassium-selective leak channel with two pore domains cloned from
Drosophila melanogaster by expression in Saccharomyces cerevisiae.
PROC.NATL.ACAD.SCI.U.S.A. 93 13256-13261 (1996).
3. FINK, M. DUPRAT, F., LESAGE, F., REYES, R., ROMEY, G., HEURTEAUX, C. AND
LAZDUNSKI, M.
Cloning, functional expression and brain localization of a novel
unconventional outward rectifier K+ channel.
EMBO J. 15 6854-6862 (1996).
4. LESAGE, F., GUILLEMARE, E., FINK, M., DUPRAT, F., LAZDUNSKI, M., ROMEY,
G. AND BARHANIN, J.
TWIK-1, a ubiquitous human weakly inward rectifying K+ channel with novel
structure.
EMBO J. 15 1004-1011 (1996).
5. DUPRAT, F., LESAGE, F., FINK, M., REYES, R., HEURTEAUX, C. AND
LAZDUNSKI, M.
TASK, a human background K+ channel to sense external pH variations near
physiological pH.
EMBO J. 16 5464-5471 (1997).
6. FINK, M., LESAGE, F., DUPRAT, F., HEURTEAUX, C., REYES, R., FOSSET, M.
AND LAZDUNSKI, M.
A neuronal two P domain K+ channel stimulated by arachidonic acid and
polyunsaturated fatty acids.
EMBO J. 17 3297-3308 (1998).
7. PATEL, A.J. AND HONORE, E.
Properties and modulation of mammalian 2P-domain K+ channels.
TRENDS NEUROSCI. 24(6) 339-346 (2001).
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| Documentation | Potassium (K+) channels play a key role in many cellular functions, in both
excitable and non-excitable tissues. Among the ion channels, they form the
largest family in terms of both structure and function. K+ channel subunits
contain a conserved pore-forming motif, the P-domain, which is considered to
be an essential element of the aqueous K+-selective pore. Shaker-type and
Kir K+ channel subunits both contain a single P-domain, and four such
subunits are thought to associate to form a multimer, together with
associated auxillary (regulatory) subunits. Recently, a new class of K+
channel subunits was cloned, which is clearly distinct from the Shaker and
Kir families; the new class contains not one but two P-domains in each
subunit, and evidence suggests a complete channel may be formed by the
dimerisation of two such subunits.
The first member of this family (TOK1) cloned from S.cerevisiae [1] was
predicted to have eight potential transmembrane (TM) helices. However,
subsequently-cloned two P-domain family members from Drosophila and
mammalian species are predicted to have only four TM segments. They are
usually referred to as TWIK-related channels (Tandem of P-domains in a
Weakly Inward rectifying K+ channel) [2-6]. Functional characterisation of
these channels has revealed a diversity of properties in that they may show
inward or outward rectification, their activity may be modulated in
different directions by protein phosphorylation, and their sensitivity to
changes in intracellular or extracellular pH varies. Despite these disparate
properties, they are all thought to share the same topology of four TM
segments, including two P-domains. That TWIK-related K+ channels all produce
instantaneous and non-inactivating K+ currents, which do not display a
voltage-dependent activation threshold, suggests that they are background
(leak) K+ channels involved in the generation and modulation of the resting
membrane potential in various cell types. Further studies have revealed that
they may be found in many species, including: plants, invertebrates and
mammals.
The TASK (TWIK-related acid-sensitive K+ channel) family contains five
members (TASK1-5), which share no more than 54% amino acid identity. These
form functional K+ channels in various cell types and encode background
K+ channels, thereby helping to set the resting membrane potential. All
members are very sensitive to variations in extracellular pH in the
physiological range, changing from fully-open to closed in approximately
0.5pH units around pH7.4. Thus, they may well constitute biological sensors
of external pH variations [7].
TASKCHANNEL is a 3-element fingerprint that provides a signature for the
TASK K+ channel. The fingerprint was derived from an initial alignment of 5
sequences: the motifs were drawn from conserved regions spanning virtually
the full alignment length, focusing on those sections that characterise
TASK channel proteins but distinguish them from related two P-domain K+
channel sequences - motif 1 is situated in the N-terminus; motif 2 spans
the second putative TM domain; and motif 3 is located in the fourth TM
domain. Three iterations on SPTR39.22_17.3f were required to reach
convergence, at which point a true set comprising 16 sequences was
identified. Several partial matches were also found, all of which are
members of the TASK family.
An update on SPTR55_38f identified a true set comprising 41 sequences,
together with 4 partial matches.
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| Sequence Titles | A2AHD2_MOUSE Potassium channel, subfamily K, member 15 - Mus musculus (Mouse).
A5WW77_DANRE Novel protein similar to vertebrate potassium channel, subfamily K, member 9 (KCNK9) - Danio rerio (Zebrafish) (Brachydanio rerio).
A6YQS3_LYMST TASK two-pore domain potassium channel - Lymnaea stagnalis (Great pond snail).
A8KB52_DANRE Putative uncharacterized protein - Danio rerio (Zebrafish) (Brachydanio rerio).
A8X4U9_CAEBR Putative uncharacterized protein - Caenorhabditis briggsae.
A8XVW8_CAEBR Putative uncharacterized protein - Caenorhabditis briggsae.
CIW9_CAVPO POTASSIUM CHANNEL SUBFAMILY K MEMBER 9 (ACID-SENSITIVE POTASSIUM CHANNEL PROTEIN TASK-3) (TWIK-RELATED ACID-SENSITIVE K+ CHANNEL 3) - Cavia porcellus (Guinea pig).
CIW9_HUMAN POTASSIUM CHANNEL SUBFAMILY K MEMBER 9 (ACID-SENSITIVE POTASSIUM CHANNEL PROTEIN TASK-3) (TWIK-RELATED ACID-SENSITIVE K+ CHANNEL 3) - Homo sapiens (Human).
KCNK9_MOUSE Potassium channel subfamily K member 9 (Acid-sensitive potassium channel protein TASK-3) (TWIK-related acid-sensitive K(+) channel 3) - Mus musculus (Mouse).
KCNK9_RAT Potassium channel subfamily K member 9 (Acid-sensitive potassium channel protein TASK-3) (TWIK-related acid-sensitive K(+) channel 3) (Two pore potassium channel KT3.2) - Rattus norvegicus (Rat).
KCNK9_XENLA Potassium channel subfamily K member 9 - Xenopus laevis (African clawed frog).
KCNKF_RAT Potassium channel subfamily K member 15 (Acid-sensitive potassium channel protein TASK-5) (TWIK-related acid-sensitive K(+) channel 5) (rTASK-5) - Rattus norvegicus (Rat).
O14649 TWIK-RELATED ACID-SENSITIVE K+ CHANNEL - HOMO SAPIENS (HUMAN).
O17185 F34D6.3 PROTEIN - Caenorhabditis elegans.
O35111 CTBAK - MUS MUSCULUS (MOUSE).
O54912 TWIK-RELATED ACID-SENSITIVE K+ CHANNEL - RATTUS NORVEGICUS (RAT).
O76790 PUTATIVE POTASSIUM CHANNEL SUBUNIT N2P20 - Caenorhabditis elegans.
O95279 TWO PORE DOMAIN K+ CHANNEL - HOMO SAPIENS (HUMAN).
Q058Y1_DROME IP11279p - Drosophila melanogaster (Fruit fly).
Q16NN0_AEDAE Putative uncharacterized protein - Aedes aegypti (Yellowfever mosquito).
Q172H0_AEDAE Putative uncharacterized protein - Aedes aegypti (Yellowfever mosquito).
Q2KTA6_RAT Potassium channel, subfamily K, member 5 (Similar to potassium channel TASK2) - Rattus norvegicus (Rat).
Q32PR9_DANRE Zgc:123271 - Danio rerio (Zebrafish) (Brachydanio rerio).
Q3T9D4_MOUSE Activated spleen cDNA, RIKEN full-length enriched library, clone:F830219D13 product:potassium channel, subfamily K, member 5, full insert sequence - Mus musculus (Mouse).
Q3ZZY0_DROME Acid-sensitive two pore domain K+ channel dTASK-7 - Drosophila melanogaster (Fruit fly).
Q3ZZY1_DROME Acid-sensitive two pore domain K+ channel dTASK-6 - Drosophila melanogaster (Fruit fly).
Q4RQY2_TETNG Chromosome 14 SCAF15003, whole genome shotgun sequence - Tetraodon nigroviridis (Green puffer).
Q4SDP6_TETNG Chromosome 10 SCAF14634, whole genome shotgun sequence - Tetraodon nigroviridis (Green puffer).
Q52LL3_HUMAN Potassium channel, subfamily K, member 15 - Homo sapiens (Human).
Q53SU2_HUMAN Putative uncharacterized protein KCNK3 (Potassium channel, subfamily K, member 3, isoform CRA_a) - Homo sapiens (Human).
Q5HZL7_XENLA LOC496362 protein - Xenopus laevis (African clawed frog).
Q5RGB0_DANRE Novel protein (Zgc:63921) - Danio rerio (Zebrafish) (Brachydanio rerio).
Q5TZ59_DANRE Novel protein similar to vertebrate potassium channel, subfamily K, member 3 (KCNK3) - Danio rerio (Zebrafish) (Brachydanio rerio).
Q5UE95_RABIT Potassium channel, subfamily K, member 5 - Oryctolagus cuniculus (Rabbit).
Q5VV76_HUMAN Potassium channel, subfamily K, member 5 (Potassium channel, subfamily K, member 5, isoform CRA_a) - Homo sapiens (Human).
Q6PFU3_DANRE Potassium channel, subfamily K, member 5 - Danio rerio (Zebrafish) (Brachydanio rerio).
Q7QC61_ANOGA AGAP002466-PA - Anopheles gambiae str. PEST.
Q9H427 DJ781B1.1 (A NOVEL PROTEIN SIMILAR TO THE ACID-SENSITIVE POTASSIUM CHANNEL PROTEIN TASK (KCNK3)) - Homo sapiens (Human).
Q9JK62 POTASSIUM CHANNEL TASK2 (TASK2 POTASSIUM CHANNEL) - Mus musculus (Mouse).
Q9VFS9 CG9637 PROTEIN - Drosophila melanogaster (Fruit fly).
Q9VHE0 CG9361 PROTEIN - Drosophila melanogaster (Fruit fly).
KCNKG_HUMAN Potassium channel subfamily K member 16 (TWIK-related alkaline pH- activated K(+) channel 1) (2P domain potassium channel Talk-1) - Homo sapiens (Human).
Q6X6Z5_HUMAN Pancreatic potassium channel TALK-1b - Homo sapiens (Human).
Q9ESM4 TWIK-RELATED ACID-SENSITIVE K+ CHANNEL SPRICE VARIANT (TASK1C) - Rattus norvegicus (Rat).
Q9ESM5 TASK1 SPLICE BVARIANT (TASK1B) - Rattus norvegicus (Rat).
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