2009 Fiscal Year Final Research Report

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

Research Project

Project/Area Number	19770116
Research Category	Grant-in-Aid for Young Scientists (B)
Allocation Type	Single-year Grants
Research Field	Functional biochemistry
Research Institution	Nigata University of Phermacy and Applied Life Sciences
Principal Investigator	YAMAGUCHI Toshio Nigata University of Phermacy and Applied Life Sciences, 薬学部, 助教 (50434452)
Project Period (FY)	2007 – 2009
Keywords	微生物 / 生体分子 / 膜蛋白質 / イオン輸送 / 対向輸送体
Research Abstract	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.