title: Crucial points within the pore as determinants of K⁺ channel conductance and gating.
abstract: While selective for K⁺, K⁺ channels vary significantly among their rate of ion permeation. Here, we probe the effect of steric hindrance and electrostatics within the ion conduction pathway on K⁺ permeation in the MthK K⁺ channel using structure-based mutagenesis combined with single-channel electrophysiology and X-ray crystallography. We demonstrate that changes in side-chain size and polarity at Ala88, which forms the constriction point of the open MthK pore, have profound effects on single-channel conductance as well as open probability. We also reveal that the negatively charged Glu92s at the intracellular entrance of the open pore form an electrostatic trap, which stabilizes a hydrated K⁺ and facilitates ion permeation. This electrostatic attraction is also responsible for intracellular divalent blockage, which renders the channel inward rectified in the presence of Ca²⁺. In light of the high structural conservation of the selectivity filter, the size and chemical environment differences within the portion of the ion conduction pathway other than the filter are likely the determinants for the conductance variations among K⁺ channels.
authors.affiliation: Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Shi
authors.forename: Weizhong
authors.initials: W
authors.lastname: Zeng
authors.forename: Sheng
authors.initials: S
authors.lastname: Ye
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Youxing
authors.initials: Y
authors.lastname: Jiang
mesh_terms: D018360:Crystallography, X-Ray; D017013:Methanobacteriaceae / Q000201:enzymology*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D055672:Static Electricity
chemical_list: D015221:Potassium Channels; D011188:Potassium