Yamaguchi Toshio, Aharon Gilad S, Sottosanto Jordan B, Blumwald Eduardo
Department of Plant Sciences, University of California, Davis, CA 95616, USA.
Proc Natl Acad Sci U S A. 2005 Nov 1;102(44):16107-12. doi: 10.1073/pnas.0504437102. Epub 2005 Oct 25.
The selective movement of ions between intracellular compartments is fundamental for eukaryotes. Arabidopsis thaliana Na(+)/H(+) exchanger 1 (AtNHX1), the most abundant vacuolar Na(+)/H(+) antiporter in A. thaliana, has important roles affecting the maintenance of cellular pH, ion homeostasis, and the regulation of protein trafficking. Previously, we have shown that the AtNHX1 C-terminal hydrophilic region localized in the vacuolar lumen plays an important role in regulating the antiporter's activity. Here, we have identified A. thaliana calmodulin-like protein 15 (AtCaM15), which interacts with the AtNHX1 C terminus. When expressed in yeast, AtCaM15 is localized in the vacuolar lumen. The transient expression of AtCaM15 in Arabidopsis leaf protoplasts showed that AtCaM15 is present in the central vacuole. The binding of AtCaM15 to AtNHX1 was Ca(2+)- and pH-dependent and decreased with increasing pH values. Our results also show that the binding of AtCaM15 to AtNHX1 modified the Na(+)/K(+) selectivity of the antiporter, decreasing its Na(+)/H(+) exchange activity. Taken together, the presence of a vacuolar calmodulin-like protein acting on the vacuolar-localized AtNHX1 C terminus in a Ca(2+)- pH-dependent manner suggests the presence of signaling entities acting within the vacuole.
离子在细胞内区室之间的选择性移动对真核生物至关重要。拟南芥Na(+)/H(+)交换蛋白1（AtNHX1）是拟南芥中最丰富的液泡Na(+)/H(+)逆向转运蛋白，在影响细胞pH值维持、离子稳态及蛋白质运输调节方面具有重要作用。此前，我们已经表明，位于液泡腔中的AtNHX1 C末端亲水区在调节逆向转运蛋白的活性中起重要作用。在此，我们鉴定出了与AtNHX1 C末端相互作用的拟南芥类钙调蛋白15（AtCaM15）。当在酵母中表达时，AtCaM15定位于液泡腔。AtCaM15在拟南芥叶原生质体中的瞬时表达表明AtCaM15存在于中央液泡中。AtCaM15与AtNHX1的结合是Ca(2+)和pH依赖性的，并且随着pH值的升高而降低。我们的结果还表明，AtCaM15与AtNHX1的结合改变了逆向转运蛋白的Na(+)/K(+)选择性，降低了其Na(+)/H(+)交换活性。综上所述，一种以Ca(2+) - pH依赖性方式作用于液泡定位的AtNHX1 C末端的液泡类钙调蛋白的存在表明液泡内存在信号传导实体。
