Functional analysis of the N-terminal region of Vibrio FlhG, a MinD-type ATPase in flagellar number control

Abstract

GTPase FlhF and ATPase FlhG are two key factors involved in regulating the flagellum number in Vibrio alginolyticus. FlhG is a paralog of the Escherichia coli cell division regulator MinD, which has a longer N-terminal region. Deleting the N-terminal region of FlhG results in cells with multiple flagella. The Q9A mutation in the DQAxxLR motif of the N-terminal region prevents it from activating the GTPase activity of FlhF in vitro and results in a multi-flagellation phenotype. The mutant FlhG protein was remarkably reduced compared to that of the wild-type protein in vivo. When the mutant FlhG was expressed at the same level as the wild-type FlhG, the number of flagella was restored to the wild-type level. Once synthesized in Vibrio cells, the N-terminal region mutation in FlhG seems not to affect the protein stability. We speculated that the flhG translation efficiency is decreased by N-terminal mutation. Our results suggest that the N-terminal region of FlhG controls the number of flagella by adjusting the FlhF activity and the amount of FlhG in vivo. We speculate that the regulation by FlhG, achieved through transcription by the master regulator FlaK, is affected by the mutations, resulting in reduced flagellar formation by FlhF.