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The Journal of Neuroscience, September 15, 2002, 22(18):7991-8001
Calmodulin Is an Auxiliary Subunit of KCNQ2/3 Potassium
Channels
Hua
Wen and
Irwin B.
Levitan
Department of Neuroscience, University of Pennsylvania School of
Medicine, Philadelphia, Pennsylvania 19104
Calmodulin (CaM) was identified as a KCNQ2 and KCNQ3 potassium
channel-binding protein, using a yeast two-hybrid screen. CaM is
tethered constitutively to the channel, in the absence or presence of
Ca2+, in transfected cells and also
coimmunoprecipitates with KCNQ2/3 from mouse brain. The structural
elements critical for CaM binding to KCNQ2 lie in two conserved motifs
in the proximal half of the channel C-terminal domain. Truncations and
point mutations in these two motifs disrupt the interaction. The first
CaM-binding motif has a sequence that conforms partially to the
consensus IQ motif, but both wild-type CaM and a
Ca2+-insensitive CaM mutant bind to KCNQ2. The
voltage-dependent activation of the KCNQ2/3 channel also shows no
Ca2+ sensitivity, nor is it affected by
overexpression of the Ca2+-insensitive CaM mutant.
On the other hand, KCNQ2 mutants deficient in CaM binding are unable to
generate detectable currents when coexpressed with KCNQ3 in CHO cells,
although they are expressed and targeted to the cell membrane and
retain the ability to assemble with KCNQ3. A fusion protein containing
both of the KCNQ2 CaM-binding motifs competes with the full-length
KCNQ2 channel for CaM binding and decreases KCNQ2/3 current density in
CHO cells. The correlation of CaM binding with channel function
suggests that CaM is an auxiliary subunit of the KCNQ2/3 channel.
Key words:
calmodulin; KCNQ channels; M current; IQ motif; channel
modulation; auxiliary subunit; Ca2+-independent
interaction
Copyright © 2002 Society for Neuroscience 0270-6474/02/22187991-11$05.00/0
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