title: Mutational analysis of block and facilitation of HERG current by a class III anti-arrhythmic agent, nifekalant.
abstract: Chemicals and toxins are useful tools to elucidate the structure-function relationship of various proteins including ion channels. The HERG channel is blocked by many compounds and this may cause life-threatening cardiac arrhythmia. Besides block, some chemicals such as the class III anti-arrhythmic agent nifekalant stimulate HERG at low potentials by shifting its activation curve towards hyperpolarizing voltages. This is called "facilitation". Here, we report mutations and simulations analyzing the association between nifekalant and channel pore residues for block and facilitation. Alanine-scanning mutagenesis was performed in the pore region of HERG. The mutations at the base of the pore helix (T623A), the selectivity filter (V625A) and the S6 helix (G648A, Y652A and F656A) abolished and S624A attenuated both block and facilitation induced by the drug. On the other hand, the mutation of other residues caused either an increase or a decrease in nifekalant-induced facilitation without affecting block. An open-state homology model of the HERG pore suggested that T623, S624, Y652 and F656 faced the central cavity, and were positioned within geometrical range for the drug to be able to interact with all of them at the same time. Of these, S649 was the only polar residue located within possible interaction distance from the drug held in its blocking position. Further mutations and flexible-docking simulations suggest that the size, but not the polarity, of the side chain at S649 is critical for drug induced facilitation.
authors.affiliation: Department of Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Hosaka
authors.forename: Miki
authors.initials: M
authors.lastname: Iwata
authors.forename: Narutoshi
authors.initials: N
authors.lastname: Kamiya
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Yamada
authors.forename: Kengo
authors.initials: K
authors.lastname: Kinoshita
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Fukunishi
authors.forename: Kenji
authors.initials: K
authors.lastname: Tsujimae
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hibino
authors.forename: Yoshifusa
authors.initials: Y
authors.lastname: Aizawa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Inanobe
authors.forename: Haruki
authors.initials: H
authors.lastname: Nakamura
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kurachi
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D003198:Computer Simulation; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D018014:Gene Transfer Techniques; D006801:Humans; D008564:Membrane Potentials; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011487:Protein Conformation; D011744:Pyrimidinones / Q000494:pharmacology*; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D000889:Anti-Arrhythmia Agents; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D026902:Potassium Channel Blockers; D011744:Pyrimidinones; C076259:nifekalant; D011188:Potassium