title: Hydrophobic interaction between contiguous residues in the S6 transmembrane segment acts as a stimuli integration node in the BK channel.
abstract: Large-conductance Ca(2+)- and voltage-activated K(+) channel (BK) open probability is enhanced by depolarization, increasing Ca(2+) concentration, or both. These stimuli activate modular voltage and Ca(2+) sensors that are allosterically coupled to channel gating. Here, we report a point mutation of a phenylalanine (F380A) in the S6 transmembrane helix that, in the absence of internal Ca(2+), profoundly hinders channel opening while showing only minor effects on the voltage sensor active-resting equilibrium. Interpretation of these results using an allosteric model suggests that the F380A mutation greatly increases the free energy difference between open and closed states and uncouples Ca(2+) binding from voltage sensor activation and voltage sensor activation from channel opening. However, the presence of a bulky and more hydrophobic amino acid in the F380 position (F380W) increases the intrinsic open-closed equilibrium, weakening the coupling between both sensors with the pore domain. Based on these functional experiments and molecular dynamics simulations, we propose that F380 interacts with another S6 hydrophobic residue (L377) in contiguous subunits. This pair forms a hydrophobic ring important in determining the open-closed equilibrium and, like an integration node, participates in the communication between sensors and between the sensors and pore. Moreover, because of its effects on open probabilities, the F380A mutant can be used for detailed voltage sensor experiments in the presence of permeant cations.
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile.
authors.forename: Willy
authors.initials: W
authors.lastname: Carrasquel-Ursulaez
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile.
authors.forename: Gustavo F
authors.initials: GF
authors.lastname: Contreras
authors.affiliation: Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile.
authors.forename: Romina V
authors.initials: RV
authors.lastname: Sepúlveda
authors.affiliation: Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile.
authors.forename: Daniel
authors.initials: D
authors.lastname: Aguayo
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile Centro de Bioinformática y Biología Integrativa and Doctorado en Biotecnología, Facultad de Ciencias Biológicas, Universidad Andres Bello, Santiago 8370146, Chile.
authors.forename: Fernando
authors.initials: F
authors.lastname: González-Nilo
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile ramon.latorre@uv.cl carlos.gonzalezl@uv.cl.
authors.forename: Carlos
authors.initials: C
authors.lastname: González
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso and Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103, Chile ramon.latorre@uv.cl carlos.gonzalezl@uv.cl.
authors.forename: Ramón
authors.initials: R
authors.lastname: Latorre
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000235:genetics; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000235:genetics; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D014981:Xenopus
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D010649:Phenylalanine; D008239:Lysine; D002118:Calcium