C-Terminal β9-Strand of the Cyclic Nucleotide-Binding Homology Domain Stabilizes Activated States of Kv11.1 Channels

Chai Ann Ng,Adam P Hill,Peter S Tan,Matthew D Perry,Jamie I Vandenberg,Ying Ke,Paolo Carloni

doi:10.1371/journal.pone.0077032

Abstract

Kv11.1 potassium channels are important for regulation of the normal rhythm of the heartbeat. Reduced activity of Kv11.1 channels causes long QT syndrome type 2, a disorder that increases the risk of cardiac arrhythmias and sudden cardiac arrest. Kv11.1 channels are members of the KCNH subfamily of voltage-gated K+ channels. However, they also share many similarities with the cyclic nucleotide gated ion channel family, including having a cyclic nucleotide-binding homology (cNBH) domain. Kv11.1 channels, however, are not directly regulated by cyclic nucleotides. Recently, crystal structures of the cNBH domain from mEAG and zELK channels, both members of the KCNH family of voltage-gated potassium channels, revealed that a C-terminal β9-strand in the cNBH domain occupied the putative cyclic nucleotide-binding site thereby precluding binding of cyclic nucleotides. Here we show that mutations to residues in the β9-strand affect the stability of the open state relative to the closed state of Kv11.1 channels. We also show that disrupting the structure of the β9-strand reduces the stability of the inactivated state relative to the open state. Clinical mutations located in this β9-strand result in reduced trafficking efficiency, which suggests that binding of the C-terminal β9-strand to the putative cyclic nucleotide-binding pocket is also important for assembly and trafficking of Kv11.1 channels.

Highlights

The KCNH gene family encodes three subtypes of voltagegated K+ channels, the ether-a-go-go (EAG, Kv10.x), the ether-a-go-gorelated (ERG, Kv11.x) and the ether-a-go-go-like (ELK, Kv12.x) voltage-gated K+ channels [1]
The second difference can be found at the C-terminus, where the aC of the cyclic nucleotide-binding homology (cNBH) domain in mHCN2 is replaced with a shortened a-helix and a short b-strand (b9) in both the zELK and mEAG cNBH domain structures (Figure 1B, green and blue)
Crystal structures have been obtained for the cNBH domains of both mEAG and zELK channels [13,14]

Summary

Introduction

The KCNH gene family encodes three subtypes of voltagegated K+ channels, the ether-a-go-go (EAG, Kv10.x), the ether-a-go-gorelated (ERG, Kv11.x) and the ether-a-go-go-like (ELK, Kv12.x) voltage-gated K+ channels [1]. The KCNH subfamily of voltage-gated K+ channels share many structural and functional similarities with the KCNA (Shaker, Kv1.x) family of voltage-gated K+ channels They assemble as tetramers, with each subunit containing cytoplasmic N-terminal and C-terminal domains, as well as a transmembrane region containing the voltage sensor domain, composed of four transmembrane helices (S1–S4), and a pore domain, composed of two transmembrane helices (S5–S6) along with an intervening Ploop segment that contains the K+ selectivity filter. The cNBH domain in the KCNH family lacks the critical arginine residue that binds the phosphate headgroup of cAMP [12] and the b-roll cavity has an overall net negative charge which makes it unfavourable for cAMP binding and in contrast to cNG and HCN channels, the KCNH family of channels do not appear to be directly regulated by binding of cyclic nucleotides [12,13]

Methods

Results

Conclusion