| Literature References | 1. MILLER, C.
An overview of the potassium channel family.
GENOME BIOL. 1(4) 1-5 (2000).
2. ASHCROFT, F.M.
Ca2+ activated K+ channels.
IN ION CHANNELS AND DISEASE, ACADEMIC PRESS, 2000, PP.125-133.
3. VERGARA, C., LATORRE, R., MARRION, N.V. AND ADELMAN, J.P.
Calcium-activated potassium channels.
CURR.OPIN.NEUROBIOL. 8(3) 321-329 (1998).
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| Documentation | Potassium ion (K+) channels are a structurally diverse group of proteins
that facilitate the flow of K+ ions across cell membranes. They are
ubiquitous, being present in virtually all cell types. Activation of K+
channels tends to hyperpolarise cells, reducing the membrane's electrical
resistance, dampening nervous activity. In eukaryotic cells, K+ channels
are involved in neural signalling and generation of the cardiac rhythm, and
act as effectors in signal transduction pathways involving G protein-
coupled receptors (GPCRs). In prokaryotic cells, they play a role in the
maintenance of ionic homeostasis [1].
Structurally, calcium (Ca2+) activated channels belong to the subfamily of
K+ channels whose subunits contain 6 transmembrane (TM) domains: these are
the voltage-gated K+ (Kv) channels, the KCNQ channels, the EAG-like K+
channels and 3 kinds of Ca2+-activated K+ channel (BK, IK and SK) [2]. All
K+ channels share a characteristic sequence feature: a TMxTVGYG motif that
resides between the 2 C-terminal membrane-spanning helices, and forms
the K+-selective pore domain [1].
Ca2+-activated K+ channels are a diverse group of channels that are
activated by an increase in intracellular Ca2+ concentration. They are
found in the majority of nerve cells, where they modulate cell excitability
and action potential. Three types of Ca2+-activated K+ channel have been
characterised, termed small-conductance (SK), intermediate conductance (IK)
and large conductance (BK) respectively [2-3].
BK channels (also referred to as maxi-K channels) are widely expressed
in the body, being found in glandular tissue, smooth and skeletal muscle,
as well as in neural tissues. They have been demonstrated to regulate
arteriolar and airway diameter, and also neurotransmitter release. Each
channel complex is thought to be composed of 2 types of subunit: the pore-
forming (alpha) subunits and smaller accessory (beta) subunits.
The alpha subunit of the BK channel was initially thought to share the
characteristic 6TM organisation of the voltage-gated K+ channels. However,
the molecule is now thought to possess an additional TM domain, with an
extracellular N-terminus and intracellular C-terminus. This C-terminal
region contains 4 predominantly hydrophobic domains, which are also thought
to lie intracellularly. The extracellular N-terminus and the first TM region
are required for modulation by the beta subunit. The precise location of the
Ca2+-binding site that modulates channel activation remains unknown, but it
is thought to lie within the C-terminal hydrophobic domains.
BKCHANNELA is an 8-element fingerprint that provides a signature for the
calcium-activated BK potassium channel alpha subunit. The fingerprint was
derived from an initial alignment of 2 sequences: the motifs were drawn
from conserved regions spanning the full alignment length, focusing on those
sections that characterise the BK channel alpha subunits but distinguish
them from other members of the K+ channel superfamily. Two iterations on
SPTR39_14f were required to reach convergence, at which point a true set
comprising 24 sequences was identified. Several partial matches were also
found, all of which are members of the calcium-dependent BK potassium
channel family that match only 4 or 5 motifs.
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| Sequence Titles | O12942 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Gallus gallus (Chicken).
O18866 CALCIUM-ACTIVATED POTASSIUM CHANNEL ALPHA SUBUNIT - Sus scrofa (Pig).
O18867 CALCIUM-ACTIVATED POTASSIUM CHANNEL ALPHA SUBUNIT - Macaca mulatta (Rhesus macaque).
O46371 LARGE CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNEL ALPHA SUBUNIT - Oryctolagus cuniculus (Rabbit).
O55180 RAT-SLOWPOKE-ALPHA - Rattus norvegicus (Rat).
O73728 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Trachemys scripta (Red-eared slider turtle).
O73729 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Trachemys scripta (Red-eared slider turtle).
O73730 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Trachemys scripta (Red-eared slider turtle).
O73731 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Trachemys scripta (Red-eared slider turtle).
O93569 CALCIUM-ACTIVATED POTASSIUM CHANNEL ALPHA SUBUNIT - Gallus gallus (Chicken).
Q08460 SLOWPOKE HOMOLOG, POTASSIUM CHANNEL, CALCIUM-ACTIVATED (CALCIUM-ACTIVATED POTASSIUM CHANNEL) (SLOWPOKE HOMOLOG PROTEIN) - Mus musculus (Mouse).
Q12917 CALCIUM DEPENDENT POTASSIUM CHANNEL ALPHA SUBUNIT - Homo sapiens (Human).
Q12921 CALCIUM ACTIVATED POTASSIUM CHANNEL - Homo sapiens (Human).
Q12960 LARGE-CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNEL - Homo sapiens (Human).
Q13150 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Homo sapiens (Human).
Q28265 CALCIUM ACTIVATED POTASSIUM CHANNEL PROTEIN - Canis familiaris (Dog).
Q62976 CALCIUM ACTIVATED POTASSIUM CHANNEL - Rattus norvegicus (Rat).
Q98951 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Gallus gallus (Chicken).
Q9R196 LARGE CONDUCTANCE CALCIUM ACTIVATED POTASSIUM BK CHANNEL STREX-1 VARIANT - Mus musculus (Mouse).
Q9TT88 MAXI-K CHANNEL ALPHA SUBUNIT - Oryctolagus cuniculus (Rabbit).
Q9UBB0 CALCIUM-ACTIVATED POTASSIUM CHANNEL ALPHA SUBUNIT - Homo sapiens (Human).
Q9UQK6 BKCA ALPHA SUBUNIT - Homo sapiens (Human).
Q9W7J2 CALCIUM-ACTIVATED POTASSIUM CHANNEL ISOFORM THC7 - Trachemys scripta (Red-eared slider turtle) (Pseudemys scripta).
Q9WUI3 LARGE-CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNEL - Rattus norvegicus (Rat).
Q24369 CALCIUM ACTIVATED POTASSIUM CHANNEL - Drosophila melanogaster (Fruit fly).
Q9TWA1 CALCIUM-ACTIVATED POTASSIUM CHANNEL - Drosophila melanogaster (Fruit fly).
Q9VC51 SLO PROTEIN - Drosophila melanogaster (Fruit fly).
O54982 POTASSIUM LARGE CONDUCTANCE PH-SENSITIVE CHANNEL, SUBFAMILY M, ALPHA MEMBER 3 (PH SENSITIVE MAXI K+ CHANNEL) - Mus musculus (Mouse).
Q9U268 Y51A2D.19 PROTEIN - Caenorhabditis elegans.
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