Auxiliary KCNE subunits modulate both homotetrameric Kv2.1 and heterotetrameric Kv2.1/Kv6.4 channels.

Jens-Peter David,Nicole Schmitt,Elke Bocksteins,Jeroen I Stas

doi:10.1038/srep12813

Abstract

The diversity of the voltage-gated K+ (Kv) channel subfamily Kv2 is increased by interactions with auxiliary β-subunits and by assembly with members of the modulatory so-called silent Kv subfamilies (Kv5-Kv6 and Kv8-Kv9). However, it has not yet been investigated whether these two types of modulating subunits can associate within and modify a single channel complex simultaneously. Here, we demonstrate that the transmembrane β-subunit KCNE5 modifies the Kv2.1/Kv6.4 current extensively, whereas KCNE2 and KCNE4 only exert minor effects. Co-expression of KCNE5 with Kv2.1 and Kv6.4 did not alter the Kv2.1/Kv6.4 current density but modulated the biophysical properties significantly; KCNE5 accelerated the activation, slowed the deactivation and steepened the slope of the voltage-dependence of the Kv2.1/Kv6.4 inactivation by accelerating recovery of the closed-state inactivation. In contrast, KCNE5 reduced the current density ~2-fold without affecting the biophysical properties of Kv2.1 homotetramers. Co-localization of Kv2.1, Kv6.4 and KCNE5 was demonstrated with immunocytochemistry and formation of Kv2.1/Kv6.4/KCNE5 and Kv2.1/KCNE5 complexes was confirmed by Fluorescence Resonance Energy Transfer experiments performed in HEK293 cells. These results suggest that a triple complex consisting of Kv2.1, Kv6.4 and KCNE5 subunits can be formed. In vivo, formation of such tripartite Kv2.1/Kv6.4/KCNE5 channel complexes might contribute to tissue-specific fine-tuning of excitability.

Highlights

IntroductionThe KCNE family consists of five members, KCNE1-5 ( known as MinK (KCNE1) and MinK-related proteins (MiRP) 1–4 (KCNE2-5))
To accommodate a variety of functions, the Kv2.1 channel diversity is increased through different mechanisms: i) heterotetramerization with modulatory α -subunits of the Kv5, Kv6, Kv8 and Kv9 subfamilies, ii) post-translational modifications such asphosphorylation and SUMOylation[22], and iii) association with auxiliary β -subunits such as KChAP3, AMIGO4 and KCNE proteins
These studies revealed that human KCNE2 and KCNE3 significantly slowed the activation of rat Kv2.1 currents at + 60 mV while KCNE1 had a smaller, still significant, effect[5,6]

Summary

Introduction

The KCNE family consists of five members, KCNE1-5 ( known as MinK (KCNE1) and MinK-related proteins (MiRP) 1–4 (KCNE2-5)). They harbor a single transmembrane α -helix, an extracellular N-terminus and an intracellular C-terminus. We sought to investigate whether auxiliary β -subunits and modulatory α -subunits can simultaneously associate with Kv α -subunits into functional tripartite channel complexes. To this end, we examined the effect of co-expressing human Kv2.1 and the modulatory α -subunit Kv6.4 with auxiliary β -subunits of the KCNE family

Methods

Results

Conclusion