Alkali cation selectivity of the wheat root high-affinity potassium transporter HKT1
Alkali cation selectivity of the wheat root high-affinity potassium transporter HKT1
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DOI：
10.1046/j.1365-313x.1996.10050869.x
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发表时间：
1996-11-01
期刊：
影响因子：
7.2
通讯作者：
Schroeder, JI
中科院分区：
文献类型：
--
作者：
Gassmann, W;Rubio, F;Schroeder, JI
小麦根高亲和力K+转运蛋白HKT1是一种钠偶联钾共吸收转运蛋白。在毒性毫摩尔水平的钠(Na+)时，HKT1介导低亲和力的Na+摄取，而钾(K+)摄取被阻断。在根中，低亲和力的Na+吸收和K+吸收的抑制导致了Na+的毒害。本文研究了在不同离子条件下，在非洲爪哇卵母细胞和酵母中表达的HKT1在稳态条件下对碱性阳离子的选择性。结果表明，HKT1对Rb+、Cs+和Li+对K+和Na+这两种生理活性阳离子的吸收具有很高的选择性。此外，Rb+和Cs+，以及细胞外K+超过Na+，部分地减少或阻断HKT1介导的K+-Na+摄取。此外，K+、Rb+和Cs+还能有效地减少HKT1介导的外向电流，从而引起去极化。在酵母中，HKT1可以产生高亲和力的RBF摄取，其摄取率大约是K+摄取率的15倍。酵母中Rb+的内流可以通过酵母质膜质子泵平衡大于或等于35倍的HKT1 Rb+电导的能力来调节。提出了HKT1活性的模型，包括一个高亲和力的K+结合部位和一个高亲和力的Na+结合部位，以及K+、Na+和其他碱性阳离子与这两个结合部位的竞争作用。本文还讨论了这些结果对植物生理K+和Na+吸收的可能影响。
The wheat root high-affinity K+ transporter HKT1 functions as a sodium-coupled potassium co-uptake transporter. At toxic millimolar levels of sodium (Na+), HKT1 mediates low-affinity Na+ uptake while potassium (K+) uptake is blocked. In roots, low-affinity Na+ uptake and inhibition of K+ uptake contribute to Na+ toxicity. In the present study, the selectivity among alkali cations of HKT1 expressed in Xenopus oocytes and yeast was investigated under various ionic conditions at steady state. The data show that HKT1 is highly selective for uptake of the two physiologically significant alkali cations, K+ and Na+ over Rb+, Cs+ and Li+. In addition, Rb+ and Cs+, and an excess of extracellular K+ over Na+, are shown to partially reduce or block HKT1-mediated K+-Na+ uptake. Furthermore, K+, Rb+ and Cs+ also effectively reduce outward currents mediated by HKT1, thereby causing depolarizations. In yeast, HKT1 can produce high-affinity Rbf uptake at approximately 15-fold lower rates than for K+. Rb+ influx in yeast can be mediated by the ability of the yeast plasma membrane proton pump to balance the greater than or equal to 35-fold lower HKT1 conductance for Rb+. A model for HKT1 activity is presented involving a high-affinity K+ binding site and a high-affinity Na+ binding site, and competitive interactions of K+, Na+ and other alkali cations for binding to these two sites. Possible implications of the presented results for physiological K+ and Na+ uptake in plants are discussed.