Characterization of a novel missense mutation E637K in the pore-S6 loop of HERG in a patient with long QT syndrome.
OBJECTIVE
In a 32-year-old woman with marked QT prolongation (QTc=0.61 s) and repeated episodes of syncope, we identified a single pertinent base substitution (G to A at 1909) in HERG by genetic analysis. This novel missense mutation is predicted to cause an amino acid substitution of lysine for glutamic acid at position 637 (E637K) in the pore-S6 loop. Therefore, we investigated the role of a glutamic acid at the vicinity of the pore in HERG channels by mutating it to a lysine.


METHODS
We characterized the electrophysiological properties of the E637K mutation using a Xenopus oocyte heterologous expression system.


RESULTS
Injection of the E637K mutant cRNA alone into Xenopus oocytes did not result in any expression of detectable currents. Coexpression of wild-type (WT) and E637K (E637K/WT) elicited only about 30% of the control peak tail current that was expected from expression of WT alone. Kinetic analyses revealed that E637K/WT decelerated the rate of channel activation and enhanced steady-state inactivation. Furthermore, the reversal potentials at low concentrations of K+ showed a positive shift in oocytes injected with E637K/WT compared with WT alone.


CONCLUSIONS
These results indicated that the E637K mutation causes apparent dominant negative suppression of WT HERG channel function and suggest that E637 at the Pore-S6 is a crucial component of the activation and inactivation gate of HERG channels.
Hayashi
Kenshi
K
Molecular Genetics of Cardiovascular Disorders, Division of Cardiovascular Medicine, Graduate School of Medical Science, Kanazawa University 13-1, Takara-machi, Ishikawa 920-8640, Japan. kenshi@im2.m.kanazawa-u.ac.jp
Shimizu
Masami
M
Ino
Hidekazu
H
Yamaguchi
Masato
M
Mabuchi
Hiroshi
H
Hoshi
Naoto
N
Higashida
Haruhiro
H
D000328:Adult; D000704:Analysis of Variance; D000818:Animals; D027682:Cation Transport Proteins; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D013575:Syncope / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators; D014158:Transcription, Genetic; D000071230:Transcriptional Regulator ERG; D014981:Xenopus
D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG