title: NS1643 interacts around L529 of hERG to alter voltage sensor movement on the path to activation.
abstract: Activators of hERG1 such as NS1643 are being developed for congenital/acquired long QT syndrome. Previous studies identify the neighborhood of L529 around the voltage-sensor as a putative interacting site for NS1643. With NS1643, the V1/2 of activation of L529I (-34 ± 4 mV) is similar to wild-type (WT) (-37 ± 3 mV; P > 0.05). WT and L529I showed no difference in the slope factor in the absence of NS1643 (8 ± 0 vs. 9 ± 0) but showed a difference in the presence of NS1643 (9 ± 0.3 vs. 22 ± 1; P < 0.01). Voltage-clamp-fluorimetry studies also indicated that in L529I, NS1643 reduces the voltage-sensitivity of S4 movement. To further assess mechanism of NS1643 action, mutations were made in this neighborhood. NS1643 shifts the V1/2 of activation of both K525C and K525C/L529I to hyperpolarized potentials (-131 ± 4 mV for K525C and -120 ± 21 mV for K525C/L529I). Both K525C and K525C/K529I had similar slope factors in the absence of NS1643 (18 ± 2 vs. 34 ± 5, respectively) but with NS1643, the slope factor of K525C/L529I increased from 34 ± 5 to 71 ± 10 (P < 0.01) whereas for K525C the slope factor did not change (18 ± 2 at baseline and 16 ± 2 for NS1643). At baseline, K525R had a slope factor similar to WT (9 vs. 8) but in the presence of NS1643, the slope factor of K525R was increased to 24 ± 4 vs. 9 ± 0 mV for WT (P < 0.01). Molecular modeling indicates that L529I induces a kink in the S4 voltage-sensor helix, altering a salt-bridge involving K525. Moreover, docking studies indicate that NS1643 binds to the kinked structure induced by the mutation with a higher affinity. Combining biophysical, computational, and electrophysiological evidence, a mechanistic principle governing the action of some activators of hERG1 channels is proposed.
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
authors: Jiqing
authors: J
authors: Guo
authors: Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada.
authors: Yen May
authors: YM
authors: Cheng
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
authors: James P
authors: JP
authors: Lees-Miller
authors: Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors: Laura L
authors: LL
authors: Perissinotti
authors: Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada.
authors: Tom W
authors: TW
authors: Claydon
authors: Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada.
authors: Christina M
authors: CM
authors: Hull
authors: Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada.
authors: Samrat
authors: S
authors: Thouta
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
authors: Daniel E
authors: DE
authors: Roach
authors: Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors: Serdar
authors: S
authors: Durdagi
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada; Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada. Electronic address: snoskov@ucalgary.ca.
authors: Sergei Y
authors: SY
authors: Noskov
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada. Electronic address: hduff@ucalgary.ca.
authors: Henry J
authors: HJ
authors: Duff
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003408:Cresols / Q000378:metabolism* / Q000494:pharmacology*; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D005470:Fluorometry; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D009154:Mutation; D009865:Oocytes; D018408:Patch-Clamp Techniques; D010671:Phenylurea Compounds / Q000378:metabolism* / Q000494:pharmacology*; D017433:Protein Structure, Secondary; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D003408:Cresols; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D010671:Phenylurea Compounds; C507624:1,3-bis(2-hydroxy-5-trifluoromethylphenyl)urea