Center for Synthetic Microbiology (SYNMIKRO), Philipps-University Marburg, 35043 Marburg, Germany.
Department of Chemistry, Philipps-University Marburg, 35043 Marburg, Germany.
Proc Natl Acad Sci U S A. 2020 Aug 25;117(34):20826-20835. doi: 10.1073/pnas.2006470117. Epub 2020 Aug 11.
Bacterial flagella differ in their number and spatial arrangement. In many species, the MinD-type ATPase FlhG (also YlxH/FleN) is central to the numerical control of bacterial flagella, and its deletion in polarly flagellated bacteria typically leads to hyperflagellation. The molecular mechanism underlying this numerical control, however, remains enigmatic. Using the model species , we show that FlhG links assembly of the flagellar C ring with the action of the master transcriptional regulator FlrA (named FleQ in other species). While FlrA and the flagellar C-ring protein FliM have an overlapping binding site on FlhG, their binding depends on the ATP-dependent dimerization state of FlhG. FliM interacts with FlhG independent of nucleotide binding, while FlrA exclusively interacts with the ATP-dependent FlhG dimer and stimulates FlhG ATPase activity. Our in vivo analysis of FlhG partner switching between FliM and FlrA reveals its mechanism in the numerical restriction of flagella, in which the transcriptional activity of FlrA is down-regulated through a negative feedback loop. Our study demonstrates another level of regulatory complexity underlying the spationumerical regulation of flagellar biogenesis and implies that flagellar assembly transcriptionally regulates the production of more initial building blocks.
细菌鞭毛的数量和空间排列方式各不相同。在许多物种中，MinD 型 ATP 酶 FlhG（也称为 YlxH/FleN）是控制细菌鞭毛数量的核心，其在极性鞭毛菌中的缺失通常会导致过度鞭毛化。然而，这种数量控制的分子机制仍然是个谜。使用模式物种 ，我们表明 FlhG 将鞭毛 C 环的组装与主转录调节因子 FlrA（在其他物种中称为 FleQ）的作用联系起来。虽然 FlrA 和鞭毛 C 环蛋白 FliM 在 FlhG 上有重叠的结合位点，但它们的结合依赖于 FlhG 的 ATP 依赖性二聚化状态。FliM 与 FlhG 相互作用不依赖于核苷酸结合，而 FlrA 仅与 ATP 依赖性 FlhG 二聚体相互作用，并刺激 FlhG ATP 酶活性。我们对 FlhG 在 FliM 和 FlrA 之间的伙伴切换的体内分析揭示了其在鞭毛数量限制中的机制，其中 FlrA 的转录活性通过负反馈回路下调。我们的研究表明，鞭毛生物发生的空间数量调节的另一个调节复杂性，暗示着鞭毛组装转录调节更多初始构建块的产生。
