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In the yeast potassium channel, Tok1p, the external ring of aspartate residues modulates both gating and conductance*

  • Ion Channels, Transporters
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Abstract

The yeast plasma-membrane potassium channel, Tok1p, is a voltage-dependent outward rectifier, the gating and steady-state conductance of which are conspicuously modulated by extracellular [K+] ([K+]o). Activation is slow at high [K+]o, showing time constants (τa) of ~90 ms when [K+]o is 150 mM (depolarizing step to +100 mV), and inactivation is weak (<30%) during sustained depolarization. Lowering [K+]o accelerates activation, increases peak current, and enhances inactivation, so that at 15 mM [K+]o τa is less than 50 ms and inactivation suppresses ~60% of peak current. Two negative residues, Asp292 and Asp426, near the mouth of the assembled channel, modulate both kinetics and conductance of the channel. Charge neutralization in the mutant Asp292Asn allows fast activation (τa~20 ms) at high [K+]o, peak currents diminishing with decreasing [K+]o, and fast, nearly complete, inactivation. The voltage dependence of τa persists in the mutant, but the [K+]o dependence almost disappears. Similar but smaller changes are seen in the Asp426Asn mutant, implying that pore geometry in the functional channel has twofold, not fourfold, symmetry.

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Notes

  1. MPM is an abbreviation coined by Durell and Guy [25], for the unit structure in which two transmembrane helices sandwich a single recurrent loop, penetrating the membrane from the outer surface in all potassium channels.

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Acknowledgements

The authors are indebted to Drs. T. Miosga and P. Ljungdahl for yeast strains and to Drs. Yu-Feng Zhou, Lise Heginbotham and Fred Sigworth for very helpful discussions on the manuscript. The work was supported by Grants from the Deutsche Forschungsgemeinschaft (to A.B.) and from the U.S. National Institutes of Health (GM-60696, to C.L.S.).

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Author notes

  1. H. Bihler

    Present address: Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, P.O. Box 208114, New Haven, CT, 06520, USA

  2. G. Natura

    Present address: Physiologisches Institut, Universität Jena, Teichgraben 8, 07740, Jena, Germany

Authors and Affiliations

  1. Botanisches Institut I, Universität Karlsruhe, Kaiserstrasse 12, 76128, Karlsruhe, Germany

    A. Roller, G. Natura, H. Bihler, C. Eing & A. Bertl

  2. Department of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA

    C. L. Slayman

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  1. A. Roller
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Correspondence to A. Bertl.

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*A. Roller and G. Natura contributed equally to this study.

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Roller, A., Natura, G., Bihler, H. et al. In the yeast potassium channel, Tok1p, the external ring of aspartate residues modulates both gating and conductance*. Pflugers Arch - Eur J Physiol 451, 362–370 (2005). https://doi.org/10.1007/s00424-005-1418-2

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  • DOI: https://doi.org/10.1007/s00424-005-1418-2

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