| 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.
Shaw.
IN THE ION CHANNEL FACTSBOOK, VOLUME IV, ACADEMIC PRESS, 1999, PP.559-614.
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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 5/6 and the loop region form the K+
channel pore through which the K+ ions pass [3].
The shaw gene was first isolated from Drosophila. Several vertebrate K+
channels with similar amino acid sequences were subsequently found and,
together with the Drosophila Shaw channel, now constitute the Shaw (Kv3)
family. These channels are thought to play a role in shortening of action
potential durations and modulating pre-synaptic neurotransmitter release.
In mammals, the family consists of 4 genes (Kv3.1, Kv3.2, Kv3.3 and Kv3.4).
Each gene product has its own subcellular location and function [4].
SHAWCHANNEL is a 5-element fingerprint that provides a signature for the
Shaw voltage-gated K+ channel family. The fingerprint was derived from an
initial alignment of 6 sequences: the motifs were drawn from conserved
regions spanning the full alignment lenth: motifs 1 and 2 reside within the
N-terminus; motif 3 spans the N-terminus and part of TM domain 1; motif 4
spans the loop between TM domains 2 and 3; and motif 5 resides in the
C-terminal domain. Three iterations on SPTR39_14f were required to reach
convergence, at which point a true set comprising 18 sequences was
identified.
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