Na+ conductivity of the Na+-driven flagellar motor complex composed of unplugged wild-type or mutant PomB with PomA.

PomA and PomB form the stator complex, which functions as a Na+ channel, in the Na+-driven flagellar motor of Vibrio alginolyticus. The plug region of PomB is thought to regulate the Na+ flow and to suppress massive ion influx through the stator channel. In this study, in order to measure the Na+ conductivity of the unplugged stator, we over-produced a plug-deleted stator of the Na+-driven flagellar motor in Escherichia coli. The over-production of the plug-deleted stator in E. coli cells caused more severe growth inhibition than in Vibrio cells and that growth inhibition depended on the Na+ concentration in the growth medium. Measurement of intracellular Na+ concentration by flame photometry and fluorescent analysis with a Na+ indicator, Sodium Green, revealed that over-production of the plug-deleted stator increased the Na+ concentration in cell. Some mutations in the channel region of PomB or in the cytoplasmic region of PomA suppressed both the growth inhibition and the increase in intracellular Na+ concentration. These results suggest that the level of growth inhibition correlates with the intracellular Na+ concentration, probably due to the Na+ conductivity through the stator due to the mutations. [ABSTRACT FROM AUTHOR]