pH-dependent regulation of the multi-subunit cation/proton antiporter Pha1 system from Sinorhizobium meliloti.
pH-dependent regulation of the multi-subunit cation/proton antiporter Pha1 system from Sinorhizobium meliloti.
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DOI：
10.1099/mic.0.028563-0
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发表时间：
2009-08
期刊：
影响因子：
1.5
通讯作者：
Toshio Yamaguchi;F. Tsutsumi;P. Putnoky;M. Fukuhara;Tatsunosuke Nakamura
中科院分区：
文献类型：
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作者：
Toshio Yamaguchi;F. Tsutsumi;P. Putnoky;M. Fukuhara;Tatsunosuke Nakamura
苜蓿中华根瘤菌pha 1基因簇（pha 1A '-G）是苜蓿中华根瘤菌正常侵入植物根组织的必要组成部分。由于pha 1区的突变使S.苜蓿属植物细胞对K（+）和碱敏感，并且因为与先前表征的多亚基阳离子/H（+）反向转运蛋白（Mrp反向转运蛋白）具有高度的氨基酸序列相似性。然而，Pha 1系统的详细输运性质尚未确定。有趣的是，与Pha 1系统不同，大多数Mrp反向转运蛋白对Na（+）具有高度选择性。在这里，我们报告的Pha 1系统在大肠杆菌中的功能表达和阳离子/H（+）反向转运活性的测量。我们发现，Pha 1系统确实是一个K（+）/H（+）逆向转运蛋白，在弱碱性条件下具有最佳pH值。此外，我们发现Pha 1系统可以转运Na（+），这是出乎意料的pha 1突变体的表型分析。此外，我们证明，阳离子选择性的Pha 1系统的改变时，pH值从最佳降低。Na（+）/H（+）和K（+）/H（+）逆向转运活性在酸转移过程中的下调可能是通过不同的途径发生的，这可能表明Pha 1系统的K（+）/H（+）和Na（+）/H（+）逆向转运活性存在不同的调节机制。
The pha1 gene cluster (pha1A'-G) of Sinorhizobium meliloti has previously been characterized as a necessary component for proper invasion into plant root tissue. It has been suggested to encode a multi-subunit K(+)/H(+) antiporter, since mutations in the pha1 region rendered S. meliloti cells sensitive to K(+) and alkali, and because there is high amino acid sequence similarity to previously characterized multi-subunit cation/H(+) antiporters (Mrp antiporters). However, the detailed transport properties of the Pha1 system are yet to be determined. Interestingly, most of the Mrp antiporters are highly selective for Na(+), unlike the Pha1 system. Here, we report the functional expression of the Pha1 system in Escherichia coli and the measurement of cation/H(+) antiport activity. We showed that the Pha1 system is indeed a K(+)/H(+) antiporter with a pH optimum under mildly alkaline conditions. Moreover, we found that the Pha1 system can transport Na(+); this was unexpected based on previous phenotypic analyses of pha1 mutants. Furthermore, we demonstrated that the cation selectivity of the Pha1 system was altered when the pH was lowered from the optimum. The downregulation of Na(+)/H(+) and K(+)/H(+) antiport activities upon acidic shift appeared to occur via different processes, which might indicate the presence of distinct mechanisms for the regulation of the K(+)/H(+) and Na(+)/H(+) antiport activities of the Pha1 system.