Open conformation of hERG channel turrets revealed by a specific scorpion toxin BmKKx2.

You-Tian Hu,Tian Li,Wen-Xin Li,Zhi-Jian Cao,Jing Feng,Jun Hu,Ying-Liang Wu,Yi-Mei Du,Jing-Jing Wei

doi:10.1186/2045-3701-4-18

Abstract

BackgroundThe human ether-a-go-go-related gene potassium channel (hERG) has an unusual long turret, whose role in recognizing scorpion toxins remains controversial. Here, BmKKx2, the first specific blocker of hERG channel derived from scorpion Mesobuthus martensii, was identified and the turret role of hERG channel was re-investigated using BmKKx2 as a molecular probe.ResultsBmKKx2 was found to block hERG channel with an IC50 of 6.7 ± 1.7 nM and share similar functional surface with the known hERG channel inhibitor BeKm-1. The alanine-scanning mutagenesis data indicate that different residue substitutions on hERG channel by alanine decreased the affinities of toxin BmKKx2 by about 10-fold compared with that of wild-type hERG channel, which reveals that channel turrets play a secondary role in toxin binding. Different from channel turret, the pore region of hERG channel was found to exert the conserved and essential function for toxin binding because the mutant hERG-S631A channel remarkably decreased toxin BmKKx2 affinity by about 104-fold.ConclusionsOur results not only revealed that channel turrets of hERG channel formed an open conformation in scorpion toxin binding, but also enriched the diversity of structure-function relationships among the different potassium channel turrets.

Highlights

The human ether-a-go-go-related gene potassium channel has an unusual long turret, whose role in recognizing scorpion toxins remains controversial
The structure-function relationship of toxin BmKKx2 indicated that it shared the same critical residues (Tyr11, Lys18, Arg20 and Lys23) as those of nearly identical scorpion toxin BeKm-1 (Figures 3 and 7A-B, and Table 1) [12]. These results demonstrated that toxin BmKKx2 was a useful molecule probe to explore the functional role of human ether-a-go-go-related gene potassium channel (hERG) channel turrets in toxin recognition
With the help of a new specific scorpion toxin BmKKx2, the first specific blocker for hERG channels from scorpion Mesobuthus martensii, the turret role of hERG channel was re-investigated through the alanine-scanning mutagenesis

Summary

Introduction

The human ether-a-go-go-related gene potassium channel (hERG) has an unusual long turret, whose role in recognizing scorpion toxins remains controversial. BmKKx2, the first specific blocker of hERG channel derived from scorpion Mesobuthus martensii, was identified and the turret role of hERG channel was re-investigated using BmKKx2 as a molecular probe. Due to the channel structure complexity and technique challenge, there are a few crystal structures of eukaryotic potassium channels, such as Kv1.2, Kir2.2 and Kir3.2 [3,4,5]. Comparison of these crystal structures reveals essential conformation differences in the extracellular pore entryway that includes turret and filter regions. Other structural features of channel turrets were revealed by the specific scorpion toxins as the molecular probes.

Methods

Results

Discussion

Conclusion