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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 .
The KCNQ2 channel subunit is thought to form active channels by hetero-
tetramerisation with KCNQ3, although some K+ channel activity does results
from the expression of KCNQ2 alone . Channel function is modulated by
phosphorylation, since experiments have demonstrated that an increase in
intracellular cAMP concentration can enhance channel activity .
Frameshift mutations in both KCNQ2 and KCNQ3 are associated with benign
familial neonatal epilepsy , a disorder where an infant begins to suffer
convulsions, within the first three days of life. These symptoms usually
disappear after approximately three months, but affected individuals have a
higher than average chance of subsequently developing epilepsy (10-15%), in
later life .
KCNQ2CHANNEL is a 4-element fingerprint that provides a signature for the
KCNQ2 voltage-gated potassium channel. The fingerprint was derived from an
initial alignment of 16 sequences: the motifs were drawn from conserved
regions spanning the N-terminal third of the alignment, focusing on those
sections that characterise the KCNQ2 channel but distinguish it from other
members of the K+ channel superfamily - motifs 1 and 2 span the N-terminal
intracellular region; and motifs 3 and 4 span putative TM domains 1 and 2,
and the extracellular loop connecting them. Two iterations on SPTR39_14f
were required to reach convergence, at which point a true set comprising 17
sequences was identified. A single partial match was also found, CIQ4_HUMAN,
the closely related human KCNQ4 channel, which matches motifs 3 and 4.