Johansson Ingela, Wulfetange Klaas, Porée Fabien, Michard Erwan, Gajdanowicz Pawel, Lacombe Benoît, Sentenac Hervé, Thibaud Jean-Baptiste, Mueller-Roeber Bernd, Blatt Michael R, Dreyer Ingo
Laboratory of Plant Physiology and Biophysics, IBLS Plant Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK.
Plant J. 2006 Apr;46(2):269-81. doi: 10.1111/j.1365-313X.2006.02690.x.
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.
植物外向整流钾通道在气孔关闭期间介导钾离子从保卫细胞流出，并在根细胞向木质部运输以进行钾在根 - 地上部分的分配。有趣的是，尽管携带电流的离子来自细胞内部，但这些通道的门控取决于细胞外钾离子浓度。这种对钾离子的依赖性赋予了对细胞外钾离子浓度（[K⁺]）的敏感性，确保通道仅介导钾离子外流，而不管外部的[K⁺]情况如何。我们通过定点诱变研究了拟南芥钾通道SKOR的钾离子依赖性门控机制。发现影响门控内在钾离子依赖性的突变集中在孔道和第六个跨膜螺旋（S6）内，确定了膜内深处的一个“S6门控结构域”。将SKOR序列映射到来自嗜热栖热菌的电压依赖性钾通道KvAP的晶体结构上，表明S6门控结构域与孔螺旋基部之间存在相互作用，这一预测得到了该位点突变的支持。这些结果为植物中一个生理上重要的钾离子感知过程的分子基础提供了独特的见解。
