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A conserved threonine in the S1–S2 loop of KV7.2 and KV7.3 channels regulates voltage-dependent activation

  • Ion Channels, Receptors and Transporters
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Abstract

The voltage-gated potassium channels KV7.2 and KV7.3 (KCNQ2/3 genes) play an important role in regulating neuronal excitability. More than 50 KCNQ2/3 mutations have been identified to cause an inherited form of epilepsy in newborns. For two of those (E119G and S122L) found in the S1–S2 region of KV7.2, we previously showed a decreased channel availability mainly at action potential subthreshold voltages caused by a slight depolarizing shift of the activation curve. Interestingly, recent studies revealed that a threonine residue within the S1–S2 loop, highly conserved among different classes of KV channels, is crucial for both their function and surface expression. To investigate the functional role of the homologous threonine residues in KV7.2 (T114) and KV7.3 (T144) channels, we replaced them with alanine and examined the electrophysiological properties using heterologous expression in CHO cells and whole cell patch clamping. Channels comprising mutant subunits yielded decreased potassium currents with slowed activation and accelerated deactivation kinetics. However, the most striking effect was a depolarizing shift in the voltage dependence of activation reaching +30 mV upon co-expression of both mutant subunits. Potential interactions of T114 within the channel were analyzed by creating a 3D homology model of KV7.2 in an open state suggesting that this residue plays a central role in the formation of a stable interface between the S1–S2 and the S5 segment helices. This could be the explanation why substitution of the conserved threonine in KV7.2 and KV7.3 channels destabilizes the open and favors the closed state of these channels.

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Acknowledgments

This work was supported by grants from the E-rare program (EUROBFNS, Federal Ministry for Education and Research [BMBF] grant no. 01GM0804 to HL), the European Union (Epicure: LSH 037315 to HL), and the German network for rare diseases of the BMBF (IonNeurONet: 01GM1105A to SM and HL).

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Authors and Affiliations

  1. Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried Müller-Str. 27, 72076, Tübingen, Germany

    Yvonne Füll, Holger Lerche & Snezana Maljevic

  2. Myocellular Electrophysiology - Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Münster, Münster, Germany

    Guiscard Seebohm

Authors
  1. Yvonne Füll
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  2. Guiscard Seebohm
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  3. Holger Lerche
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  4. Snezana Maljevic
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Correspondence to Snezana Maljevic.

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Füll, Y., Seebohm, G., Lerche, H. et al. A conserved threonine in the S1–S2 loop of KV7.2 and KV7.3 channels regulates voltage-dependent activation. Pflugers Arch - Eur J Physiol 465, 797–804 (2013). https://doi.org/10.1007/s00424-012-1184-x

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