Zhao Jian, Shigaki Toshiro, Mei Hui, Guo Ying-Qing, Cheng Ning-Hui, Hirschi Kendal D
United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-23600, USA.
J Biol Chem. 2009 Feb 13;284(7):4605-15. doi: 10.1074/jbc.M804462200. Epub 2008 Dec 18.
In plants, high capacity tonoplast cation/H(+) antiport is mediated in part by a family of CAX (cation exchanger) transporters. Functional association between CAX1 and CAX3 has previously been inferred; however, the nature of this interaction has not been established. Here we analyze the formation of "hetero-CAX" complexes and their transport properties. Co-expressing both CAX1 and CAX3 mediated lithium and salt tolerance in yeast, and these phenotypes could not be recapitulated by expression of deregulated versions of either transporter. Coincident expression of Arabidopsis CAX1 and CAX3 occurs during particular stress responses, flowering, and seedling growth. Analysis of cax1, cax3, and cax1/3 seedlings demonstrated similar stress sensitivities. When plants expressed high levels of both CAXs, alterations in transport properties were evident that could not be recapitulated by high level expression of either transporter individually. In planta coimmunoprecipitation suggested that a protein-protein interaction occurred between CAX1 and CAX3. In vivo interaction between the CAX proteins was shown using a split ubiquitin yeast two-hybrid system and gel shift assays. These findings demonstrate cation exchange plasticity through hetero-CAX interactions.
在植物中，液泡膜阳离子/H⁺逆向转运的高能力部分由CAX（阳离子交换体）转运蛋白家族介导。此前已推断出CAX1和CAX3之间存在功能关联；然而，这种相互作用的本质尚未确定。在此，我们分析了“异源CAX”复合物的形成及其转运特性。共表达CAX1和CAX3可介导酵母中的锂耐受性和耐盐性，而这两种表型无法通过任一转运蛋白的失调版本的表达来重现。拟南芥CAX1和CAX3的同时表达发生在特定的应激反应、开花和幼苗生长过程中。对cax1、cax3和cax1/3幼苗的分析表明它们具有相似的应激敏感性。当植物高水平表达这两种CAX时，转运特性发生了明显变化，而单独高水平表达任一转运蛋白都无法重现这种变化。植物体内的共免疫沉淀表明CAX1和CAX3之间发生了蛋白质-蛋白质相互作用。使用分裂泛素酵母双杂交系统和凝胶迁移试验证明了CAX蛋白之间的体内相互作用。这些发现表明通过异源CAX相互作用实现了阳离子交换可塑性。
