Functional analysis of bacterial multi-subunit cation/H+ antiporter.

苜蓿中华根瘤菌的pha1基因簇(pha1A‘-G)已被鉴定为正常侵入植物根组织所必需的成分。有人建议编码一个多亚基的K+/H+逆向转运蛋白，因为pha1区的突变使紫花苜蓿细胞对K+和碱性敏感。然而，Pha1系统的详细传输特性尚未确定。我们在大肠杆菌中进行了Pha1系统的功能表达和阳离子/H+逆向转运蛋白活性的测定，结果表明Pha1系统确实是一个K+/H+逆向转运蛋白，在中等碱性条件下有一个最适的pH。此外，我们发现Pha1系统可以运输Na+；根据之前对pha1突变体的表型分析，这是出乎意料的。此外，我们还证明了当pH从最适pH降低时，Pha1体系的阳离子选择性发生了变化。

The pha1 gene cluster (pha1A'-G) of Sinorhizobium meliloti had 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 K+ and alkaline sensitive. However, the detailed transport properties of the Pha1 system are yet to be determined. We have conducted the functional expression of the Pha1 system in Escherichia coli and the measurement of cation/H+ antiport activity, and showed that the Pha1 system is indeed a K+/H+ antiporter with a pH optimum at mildly alkaline conditions. Moreover, we found that the Pha1 system can transport Na+; this was unexpected based on previous phenotypical analyses of pha1 mutants. Furthermore, we demonstrated that the cation selectivity of the Pha1 system was altered when the pH was lowered from its optimum pH.