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


RESULTS
BmKKx2 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.


CONCLUSIONS
Our 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.
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
You-Tian
YT
Hu
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Jun
J
Hu
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Tian
T
Li
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Jing-Jing
JJ
Wei
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Jing
J
Feng
Research Center of Ion Channelopathy, Institute of Cardiovascular Diseases, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China.
Yi-Mei
YM
Du
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Zhi-Jian
ZJ
Cao
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Wen-Xin
WX
Li
State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
Ying-Liang
YL
Wu
BmKKx2; Molecular mechanism; Pore region; Scorpion toxin; Turret; hERG channel