title: Probing binding sites and mechanisms of action of an I(Ks) activator by computations and experiments.
abstract: The slow delayed rectifier (IKs) channel is composed of the KCNQ1 channel and KCNE1 auxiliary subunit, and functions to repolarize action potentials in the human heart. IKs activators may provide therapeutic efficacy for treating long QT syndromes. Here, we show that a new KCNQ1 activator, ML277, can enhance IKs amplitude in adult guinea pig and canine ventricular myocytes. We probe its binding site and mechanism of action by computational analysis based on our recently reported KCNQ1 and KCNQ1/KCNE1 3D models, followed by experimental validation. Results from a pocket analysis and docking exercise suggest that ML277 binds to a side pocket in KCNQ1 and the KCNE1-free side pocket of KCNQ1/KCNE1. Molecular-dynamics (MD) simulations based on the most favorable channel/ML277 docking configurations reveal a well-defined ML277 binding space surrounded by the S2-S3 loop and S4-S5 helix on the intracellular side, and by S4-S6 transmembrane helices on the lateral sides. A detailed analysis of MD trajectories suggests two mechanisms of ML277 action. First, ML277 restricts the conformational dynamics of the KCNQ1 pore, optimizing K(+) ion coordination in the selectivity filter and increasing current amplitudes. Second, ML277 binding induces global motions in the channel, including regions critical for KCNQ1 gating transitions. We conclude that ML277 activates IKs by binding to an intersubunit space and allosterically influencing pore conductance and gating transitions. KCNE1 association protects KCNQ1 from an arrhythmogenic (constitutive current-inducing) effect of ML277, but does not preclude its current-enhancing effect.
authors.affiliation: Department of Physiology & Biophysics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Yu
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Physiology & Biophysics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Physiology & Biophysics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Physiology & Biophysics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Min
authors.initials: M
authors.lastname: Jiang
authors.affiliation: Department of Medicine, Pulmonary Section, University of Illinois at Chicago, Illinois; Department of Chemistry, University of Illinois at Chicago, Illinois.
authors.forename: Avia
authors.initials: A
authors.lastname: Rosenhouse-Dantsker
authors.affiliation: Department of Biology, University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Tsjerk
authors.initials: T
authors.lastname: Wassenaar
authors.affiliation: Department of Physiology & Biophysics, Virginia Commonwealth University, Richmond, Virginia. Electronic address: gtseng@vcu.edu.
authors.forename: Gea-Ny
authors.initials: GN
authors.lastname: Tseng
mesh_terms: D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D051668:Delayed Rectifier Potassium Channels / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D006168:Guinea Pigs; D007477:Ions / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D017433:Protein Structure, Secondary; D014162:Transfection
chemical_list: D051668:Delayed Rectifier Potassium Channels; D007477:Ions; D018377:Neurotransmitter Agents; D011188:Potassium