External K+ modulates the activity of the Arabidopsis potassium channel SKOR via an unusual mechanism
Plant outward-rectifying K+ channels mediate K+ efflux from guard cells during stomatal closure and from root cells into the xylem for root–shoot allocation of potassium (K). Intriguingly, the gating of these channels depends on the extracellular K+ concentration, although the ions carrying the current are derived from inside the cell . This K+ dependence confers a sensitivity to the extracellular K+ concentration ([K+]) that ensures that the channels mediate K+ efflux only, regardless of the [K+] prevailing outside. We investigated the mechanism of K+-dependent gating of the K+ channel SKOR of Arabidopsis by site-directed mutagenesis. Mutations affecting the intrinsic K+ dependence of gating were found to cluster in the pore and within the sixth transmembrane helix (S6), identifying an ‘S6 gating domain’ deep within the membrane. Mapping the SKOR sequence to the crystal structure of the voltage-dependent K+ channel KvAP from Aeropyrum pernix suggested interaction between the S6 gating domain and the base of the pore helix, a prediction supported by mutations at this site. These results offer a unique insight into the molecular basis for a physiologically important K+-sensory process in plants.
Document Type: Research Article
Affiliations: 1: Max-Planck Institute of Molecular Plant Physiology, Cooperate Research Group, 14476 Potsdam/Golm, Germany, and 2: Universität Potsdam, Institut für Biochemie und Biologie, Abteilung Molekularbiologie, Karl-Liebknecht-Strasse 24-25, Haus 20, 14476 Potsdam/Golm, Germany, 3: Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, Agro-M/CNRS/INRA/UM2, 34060 Montpellier Cedex 1, France 4: Laboratory of Plant Physiology and Biophysics, IBLS Plant Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK,
Publication date: April 1, 2006