| Literature References | 1. MILLER, C.
An overview of the potassium channel family.
GENOME BIOL. 1(4) 1-5 (2000).
2. ASHCROFT, F.M.
Voltage-gated K+ channels.
IN ION CHANNELS AND DISEASE, ACADEMIC PRESS, 2000, PP.97-123.
3. SANSOM, M.S.
Putting the parts together.
CURR.BIOL. 9(19) R738-R741 (1999).
4. CONLEY, E.C. AND BRAMMAR, W.J.
Shab.
IN THE ION CHANNEL FACTSBOOK, VOLUME IV, ACADEMIC PRESS, 1999, PP.524-558.
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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, Kv 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+ channels (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 [1-2].
The Kv family can be divided into 4 subfamilies on the basis of sequence
similarity and function: Shaker (Kv1), Shab (Kv2), Shaw (Kv3) and Shal
(Kv4). All consist of pore-forming alpha subunits that associate with
different types of beta subunit. To form a functional K+ channel pore,
4 alpha subunits and 4 beta subunits are required. The alpha subunits
have 6 well-conserved TM domains, a pore loop region and variable length
N- and C-termini. TM domains 5 and 6, and the loop region, form the K+
channel pore through which the K+ ions pass [3].
The Shab voltage-gated delayed rectifier K+ channels (also known as Kv2
channels) are responsible for much of the delayed rectifier current in
Drosophila nervous system and muscle. However, in vertebrates, Kv2 channels
have largely undetermined roles in the delayed rectifier currents of the
heart and skeletal muscle. Kv2 channels can be further divided into 2
subtypes, designated Kv2.1 and Kv2.2 [4].
The first Kv2.2 channel was cloned from rat and was originally referred to
as the circumvillate papilla delayed rectifying K+ channel or cDRK. Several
mammalian channels have subsequently been found and, together with the rat
Kv2.2 channel, form a small subfamily. They are predominantly expressed in
the interneurones; however, their roles are largely undetermined [4].
KV22CHANNEL is a 7-element fingerprint that provides a signature for the
Kv2.2 voltage-gated K+ channel. The fingerprint was derived from an initial
alignment of 4 sequences: the motifs were drawn from conserved regions
spanning the C-terminal third of the alignment, focusing on those sections
that characterise the Kv2.2 channel but distinguish it from other members of
the Shab channel family. A single iteration on SPTR39_15f was required to
reach convergence, no further sequences being identified beyond the starting
set. Several partial matches were found, all of which are closely related
members of the Shab family that match 2 or 3 motifs.
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