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Proc Natl Acad Sci U S A. 2017 Jan 31;114(5):E869-E878. doi: 10.1073/pnas.1612622114. Epub 2017 Jan 17.

Competition of calcified calmodulin N lobe and PIP2 to an LQT mutation site in Kv7.1 channel.

Author information

1
Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel.
2
Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Institute of Structural Biology, Tel Aviv University, Tel Aviv 69978, Israel.
3
Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
4
Laboratory of Structural Physiology, Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
5
Department of Physiology and Pharmacology, Sackler Faculty of Medicine and Sagol School of Neurosciences, Tel Aviv University, Tel Aviv 69978, Israel; battali@post.tau.ac.il.

Abstract

Voltage-gated potassium 7.1 (Kv7.1) channel and KCNE1 protein coassembly forms the slow potassium current IKS that repolarizes the cardiac action potential. The physiological importance of the IKS channel is underscored by the existence of mutations in human Kv7.1 and KCNE1 genes, which cause cardiac arrhythmias, such as the long-QT syndrome (LQT) and atrial fibrillation. The proximal Kv7.1 C terminus (CT) binds calmodulin (CaM) and phosphatidylinositol-4,5-bisphosphate (PIP2), but the role of CaM in channel function is still unclear, and its possible interaction with PIP2 is unknown. Our recent crystallographic study showed that CaM embraces helices A and B with the apo C lobe and calcified N lobe, respectively. Here, we reveal the competition of PIP2 and the calcified CaM N lobe to a previously unidentified site in Kv7.1 helix B, also known to harbor an LQT mutation. Protein pulldown, molecular docking, molecular dynamics simulations, and patch-clamp recordings indicate that residues K526 and K527 in Kv7.1 helix B form a critical site where CaM competes with PIP2 to stabilize the channel open state. Data indicate that both PIP2 and Ca2+-CaM perform the same function on IKS channel gating by producing a left shift in the voltage dependence of activation. The LQT mutant K526E revealed a severely impaired channel function with a right shift in the voltage dependence of activation, a reduced current density, and insensitivity to gating modulation by Ca2+-CaM. The results suggest that, after receptor-mediated PIP2 depletion and increased cytosolic Ca2+, calcified CaM N lobe interacts with helix B in place of PIP2 to limit excessive IKS current inhibition.

KEYWORDS:

KCNQ; LQT; PIP2; calmodulin; potassium channel

PMID:
28096388
PMCID:
PMC5293103
DOI:
10.1073/pnas.1612622114
[Indexed for MEDLINE]
Free PMC Article

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