Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
J Biochem. 2022 Jul 25;172(2):99-107. doi: 10.1093/jb/mvac047.
GTPase FlhF and ATPase FlhG are two key factors involved in regulating the flagellum number in Vibrio alginolyticus. FlhG is a paralogue of the Escherichia coli cell division regulator MinD and has a longer N-terminal region than MinD with a conserved DQAxxLR motif. The deletion of this N-terminal region or a Q9A mutation in the DQAxxLR motif prevents FlhG from activating the GTPase activity of FlhF in vitro and causes a multi-flagellation phenotype. The mutant FlhG proteins, especially the N-terminally deleted variant, were 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.
GTPase FlhF 和 ATPase FlhG 是参与调控 Alg 弧菌鞭毛数量的两个关键因素。FlhG 是大肠杆菌细胞分裂调控因子 MinD 的同源物，其 N 端区域比 MinD 更长，具有保守的 DQAxxLR 基序。该 N 端区域的缺失或 DQAxxLR 基序中的 Q9A 突变可阻止 FlhG 在体外激活 FlhF 的 GTPase 活性，并导致多鞭毛表型。与野生型蛋白相比，突变 FlhG 蛋白，特别是 N 端缺失变体，在体内的表达水平显著降低。当突变的 FlhG 以与野生型 FlhG 相同的水平表达时，鞭毛的数量恢复到野生型水平。一旦在弧菌细胞中合成，FlhG 中的 N 端突变似乎不会影响蛋白稳定性。我们推测 FlhG 的 N 端突变降低了翻译效率。我们的结果表明，FlhG 的 N 端区域通过调节 FlhF 活性和体内 FlhG 的含量来控制鞭毛数量。我们推测，通过主调控因子 FlaK 转录的 FlhG 调节受到突变的影响，导致 FlhF 形成的鞭毛减少。
