A residue at the cytoplasmic entrance of BK-type channels regulating single-channel opening by its hydrophobicity.
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.
Guo
Zhaohua
Z
Key Laboratory of Molecular Biophysics (Huazhong University of Science and Technology), Ministry of Education, College of Life Science and Technology, Wuhan, Hubei 430074, China.
Lv
Caixia
C
Yi
Hong
H
Xiong
Yu
Y
Wu
Yingliang
Y
Li
Wenxin
W
Xu
Tao
T
Ding
Jiuping
J
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
D051036:Large-Conductance Calcium-Activated Potassium Channels; D007532:Isoleucine; D013912:Threonine; D002118:Calcium