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An overview of the potassium channel family.
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Voltage-gated K+ channels.
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Maximal function of minimal K+ channel subunits.
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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 .
Structurally, KCNQ channels belong to the subfamily of K+ channels whose
subunits contain 6 transmembrane (TM) domains: these are the voltage-gated
K+ channels, the KCNQ channels, the EAG-like K+ channels and 3 kinds of
Ca2+-activated K+ channel (BK, IK and SK) . 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 .
KCNQ 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 . 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  and benign familial neonatal epilepsy .
KCNQCHANNEL is a 3-element fingerprint that provides a signature for the
KCNQ voltage-gated potassium channel family. The fingerprint was derived
from an initial alignment of 25 sequences: the motifs were drawn from
conserved regions spanning the N-terminal third of the alignment, focusing
on those sections that characterise the KCNQ channels but distinguish them
from other members of the K+ channel superfamily - motifs 1 and 2 span the
putative extracellular loop region between the putative TM domains 1 and 2;
and motif 3 spans the putative intracellular loop between TM domains 3 and
4. Two iterations on SPTR39_14f were required to reach convergence, at
which point a true set comprising 31 sequences was identified.