Characterization of a novel missense mutation in the pore of HERG in a patient with long QT syndrome.
BACKGROUND
A new strategy to elucidate the molecular mechanisms underlying the long QT syndrome (LQTS) is now available with genetic mutational analyses and characterization of ion channel mutations.


RESULTS
In a 26-year-old woman with LQTS, we identified a novel missense mutation in the pore of HERG by using polymerase chain reaction/single-strand conformation polymorphism (PCR/SSCP) and sequencing of her genomic DNA. The mutation resulted in an amino acid substitution of a positively charged lysine for a highly conserved uncharged asparagine at codon 629 (N629K). Whole cell, patch clamp studies were conducted in COS7 cells by transfecting with wild-type (WT) and/or the mutant N629K HERG. The WT HERG produced an I(Kr)-like, E-4031-sensitive conductance with an inward rectification. In contrast, the cells transfected with the N629K HERG did not display any time-dependent current. Cotransfection of WT and N629K HERG (at a ratio of 1:1) produced a significantly smaller conductance when compared with WT HERG (WT 59.9 +/- 7.3 pA/pF [n = 22] vs WT+N629K 5.5 +/- 2.3 pA/pF [n = 11]; P < 0.01), but did not alter K+ ion selectivity and tail current-voltage dependence. Because aprindine hydrochloride was effective in preventing ventricular tachycardias, we also tested the effect of the drug on WT HERG (I(Kr)) and KvLQT1/KCNE1 (I(Ks)) currents expressed in COS7.


CONCLUSIONS
Functional analyses of a novel missense mutation in the pore of HERG suggest that the mutation causes marked reduction of I(Kr) via a dominant negative effect.
Yoshida
H
H
Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Japan.
Horie
M
M
Otani
H
H
Takano
M
M
Tsuji
K
K
Kubota
T
T
Fukunami
M
M
Sasayama
S
S
D000328:Adult; D000818:Animals; D019556:COS Cells; D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000503:physiopathology; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014162:Transfection
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