title: A residue at the cytoplasmic entrance of BK-type channels regulating single-channel opening by its hydrophobicity.
abstract: Single large-conductance calcium-activated K(+) (BK) channels encoded by the mSlo gene usually have synchronous gating, but a Drosophila dSlo (A2/C2/E2/G5/10) splice variant (dSlo1A) exhibits very flickery openings. To probe this difference in gating, we constructed a mutant I323T. This channel exhibits four subconductance levels similar to those of dSlo1A. Rectification of the single-channel current-voltage relation of I323T decreased as [Ca(2+) ](in) increased from 10 to 300 microM. Mutagenesis suggests that the hydrophobicity of the residue at the position is important for the wild-type gating; i.e., increasing hydrophobicity prolongs open duration. Molecular dynamics simulation suggests that four hydrophobic pore-lining residues at position 323 of mSlo act cooperatively in a "shutter-like" mechanism gating the permeation of K(+) ions. Rate-equilibrium free energy relations analysis shows that the four I323 residues in an mSlo channel have a conformation 65% similar to the closed conformation during gating. Based on these observations, we suggest that the appearance of rectification and substates of BK-type channels arise from a reduction of the cooperativity among these four residues and a lower probability of being open.
authors.affiliation: Key Laboratory of Molecular Biophysics (Huazhong University of Science and Technology), Ministry of Education, College of Life Science and Technology, Wuhan, Hubei 430074, China.
authors.forename: Zhaohua
authors.initials: Z
authors.lastname: Guo
authors.forename: Caixia
authors.initials: C
authors.lastname: Lv
authors.forename: Hong
authors.initials: H
authors.lastname: Yi
authors.forename: Yu
authors.initials: Y
authors.lastname: Xiong
authors.forename: Yingliang
authors.initials: Y
authors.lastname: Wu
authors.forename: Wenxin
authors.initials: W
authors.lastname: Li
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
authors.forename: Jiuping
authors.initials: J
authors.lastname: Ding
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating; D007532:Isoleucine; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D013912:Threonine
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D007532:Isoleucine; D013912:Threonine; D002118:Calcium