Division of Biomedical Convergence, College of Biomedical Science, Kangwon National University, 1 Kangwondaehak-gil, Biomedical Science Building A-204, Chuncheon, 24341, Republic of Korea.
Sci Rep. 2022 Jul 7;12(1):10856. doi: 10.1038/s41598-022-14459-5.
Listeria monocytogenes is a pathogenic bacterium that produces flagella, the locomotory organelles, in a temperature-dependent manner. At 37 °C inside humans, L. monocytogenes employs MogR to repress the expression of flagellar proteins, thereby preventing the production of flagella. However, in the low-temperature environment outside of the host, the antirepressor GmaR inactivates MogR, allowing flagellar formation. Additionally, DegU is necessary for flagellar expression at low temperatures. DegU transcriptionally activates the expression of GmaR and flagellar proteins by binding the operator DNA in the fliN-gmaR promoter as a response regulator of a two-component regulatory system. To determine the DegU-mediated regulation mechanism, we performed structural and biochemical analyses on the recognition of operator DNA by DegU. The DegU-DNA interaction is primarily mediated by a C-terminal DNA-binding domain (DBD) and can be fortified by an N-terminal receiver domain (RD). The DegU DBD adopts a tetrahelical helix-turn-helix structure and assembles into a dimer. The DegU DBD dimer recognizes the operator DNA using a positive patch. Unexpectedly, unlike typical response regulators, DegU interacts with operator DNA in both unphosphorylated and phosphorylated states with similar binding affinities. Therefore, we conclude that DegU is a noncanonical response regulator that is constitutively active irrespective of phosphorylation.
李斯特菌是一种病原菌，它会在温度依赖的方式下产生鞭毛这一运动器官。在人体内部的 37°C 温度下，李斯特菌利用 MogR 抑制鞭毛蛋白的表达，从而阻止鞭毛的产生。然而，在宿主外的低温环境中，抗阻遏物 GmaR 会使 MogR 失活，从而促进鞭毛的形成。此外，DegU 对于低温下鞭毛的表达也是必需的。DegU 通过作为双组分调控系统的应答调控因子结合 fliN-gmaR 启动子中的操纵子 DNA 转录激活 GmaR 和鞭毛蛋白的表达。为了确定 DegU 介导的调控机制，我们对 DegU 识别操纵子 DNA 进行了结构和生化分析。DegU-DNA 相互作用主要由 C 端 DNA 结合结构域 (DBD)介导，并且可以通过 N 端接收结构域 (RD)来增强。DegU DBD 采用四螺旋-转角-螺旋结构并组装成二聚体。DegU DBD 利用正补丁识别操纵子 DNA。出乎意料的是，与典型的应答调控因子不同，DegU 在未磷酸化和磷酸化状态下与操纵子 DNA 的相互作用具有相似的结合亲和力。因此，我们得出结论，DegU 是一种非典型的应答调控因子，无论是否磷酸化，它都是组成性激活的。
