The roles of charged residues in the C-terminal region of PomA, a stator component of the Na⁺-driven flagellar motor

Division of Biological Science, Graduate School of Science, Nagoya University, Furo-Cho, Chikusa-Ku, Nagoya 464-8602, Japan

^* To whom correspondence should be addressed. Email: g44416a{at}cc.nagoya-u.ac.jp.

	Abstract

Bacterial flagellar motors use specific ion gradients to drive their rotation. It has been suggested that the electrostatic interactions between charged residues of the stator and the rotor proteins are important for rotation in E. coli. Mutational studies have indicated that the Na⁺-driven motor of V. alginolyticus may incorporate similar interactions to E. coli motor but the other electrostatic interactions between the rotor and the stator proteins may exist in the Na⁺-driven motor. Thus, we investigated the C-terminal charged residues of the stator protein, PomA, in the Na⁺-driven motor. Among eight charge-reversing mutations, PomA-K203E, R215E, and D220K did not confer motility either in the motor of V. alginolyticus or in the Na⁺-driven chimeric motor in E. coli. The overproduction of R215E and D220K but not K203E mutants impaired the motility of wild-type V. alginolyticus. The R207E mutant conferred motility in the motor of V. alginolyticus but not in the chimeric motor in E. coli. Motility of the E211K and R232E mutants was similar to that of wild-type PomA in V. alginolyticus but was greatly reduced in E. coli. Suppressor analysis suggested that R215 may engage in PomA-PomA interactions or PomA intramolecular interactions to form the stator complex.