Mutations in the pore regions of the yeast K+ channel YKC1 affect gating by extracellular K+.
The product of the Saccharomyces cerevisiae K+-channel gene YKC1 includes two pore-loop sequences that are thought to form the hydrophilic lining of the pore. Gating of the channel is promoted by membrane depolarization and is regulated by extracellular K+ concentration ([K+]o) both in the yeast and when expressed in Xenopus oocytes. Analysis of the wild-type current now shows that: (i) [K+]o suppresses a very slowly relaxing component, accelerating activation; (ii) [K+]o slows deactivation in a dose-dependent fashion; and (iii) Rb+, Cs+ and, to a lesser extent, Na+ substitute for K+ in its action on gating. We have identified single residues, L293 and A428, at equivalent positions within the two pore loops that affect the [K+]o sensitivity. Substitution of these residues gave channels with reduced sensitivity to [K+]o in macroscopic current kinetics and voltage dependence, but had only minor effects on selectivity among alkali cations in gating and on single-channel conductance. In some mutants, activation was slowed sufficiently to confer a sigmoidicity to current rise at low [K+]o. The results indicate that these residues are involved in [K+]o sensing. Their situation close to the permeation pathway points to an interaction between gating and permeation.
Vergani
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P
Laboratory of Plant Physiology and Biophysics, University of London, Wye College, Wye, Kent TN25 5AH, UK. p.vergani@wye.ac.uk
Hamilton
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D
Jarvis
S
S
Blatt
M R
MR
D002414:Cations, Monovalent / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D015640:Ion Channel Gating; D007700:Kinetics; D008672:Metals, Alkali / Q000494:pharmacology; D008962:Models, Theoretical; D016297:Mutagenesis, Site-Directed; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins
D002414:Cations, Monovalent; D008672:Metals, Alkali; D015221:Potassium Channels; D029701:Saccharomyces cerevisiae Proteins; C095220:TOK1 protein, S cerevisiae; D011188:Potassium