Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Institituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico.
mBio. 2022 Aug 30;13(4):e0148122. doi: 10.1128/mbio.01481-22. Epub 2022 Jul 25.
In alphaproteobacteria, the two-component system (TCS) formed by the hybrid histidine kinase CckA, the phosphotransfer protein ChpT, and the response regulator CtrA is widely distributed. In these microorganisms, this system controls diverse functions such as motility, DNA repair, and cell division. In and , CckA is regulated by the pseudo- histidine kinase DivL, and the response regulator DivK. However, this regulatory circuit differs for other bacterial groups. For instance, in DivK is absent and DivL consists of only the regulatory PAS domain. In this study, we report that, in Rhodobacter sphaeroides, the kinase activity of CckA is inhibited by Osp, a single domain response regulator (SDRR) protein that directly interacts with the transmitter domain of CckA. , the kinase activity of CckA was severely inhibited with an equimolar amount of Osp, whereas the phosphatase activity of CckA was not affected. We also found that the expression of is activated by CtrA creating a negative feedback loop. However, under growth conditions known to activate the TCS, the increased expression of does not parallel Osp accumulation, indicating a complex regulation. Phylogenetic analysis of selected species of revealed that Osp is widely distributed in several genera. For most of these species, we found a sequence highly similar to the CtrA-binding site in the control region of , suggesting that the TCS CckA/ChpT/CtrA is controlled by a novel regulatory circuit that includes Osp in these bacteria. The two-component systems (TCS) in bacteria in its simplest architecture consist of a histidine kinase (HK) and a response regulator (RR). In response to a specific stimulus, the HK is activated and drives phosphorylation of the RR, which is responsible of generating an adaptive response. These systems are ubiquitous among bacteria and are frequently controlled by accessory proteins. In alphaproteobacteria, the TCS formed by the HK CckA, the phosphotransferase ChpT, and the RR CtrA is widely distributed. Currently, most of the information of this system and its regulatory proteins comes from findings carried out in microorganisms where it is essential. However, this is not the case in many species, and studies of this TCS and its regulatory proteins are lacking. In this study, we found that Osp, a RR-like protein, inhibits the kinase activity of CckA in a negative feedback loop since expression is activated by CtrA. The inhibitory role of Osp and the similar action of the previously reported FixT protein, suggests the existence of a new group of RR-like proteins whose main function is to interact with the HK and prevent its phosphorylation.
在α变形菌中，由混合组氨酸激酶 CckA、磷酸转移蛋白 ChpT 和反应调节剂 CtrA 组成的双组分系统（TCS）广泛分布。在这些微生物中，该系统控制着多种功能，如运动性、DNA 修复和细胞分裂。在 和 中，CckA 受假组氨酸激酶 DivL 和反应调节剂 DivK 的调节。然而，这种调节回路在其他细菌群体中有所不同。例如，在 中，DivK 不存在，而 DivL 仅由调节 PAS 结构域组成。在这项研究中，我们报告说，在球形红杆菌中，CckA 的激酶活性受到 Osp 的抑制，Osp 是一种与 CckA 的发送器结构域直接相互作用的单结构域反应调节剂（SDRR）蛋白。当用等摩尔量的 Osp 处理时，CckA 的激酶活性受到严重抑制，而 CckA 的磷酸酶活性不受影响。我们还发现，CtrA 的表达激活了 ，形成了一个负反馈回路。然而，在已知激活 TCS 的生长条件下， 的表达增加并不与 Osp 积累平行，表明存在复杂的调节。对 的选定种属的系统发育分析表明，Osp 广泛分布于几个属中。对于这些物种中的大多数，我们在 的控制区中发现了一个与 CtrA 结合位点高度相似的序列，表明在这些细菌中，TCS CckA/ChpT/CtrA 受到包括 Osp 在内的新型调节回路的控制。
细菌中的双组分系统（TCS）在其最简单的结构中由组氨酸激酶（HK）和反应调节剂（RR）组成。响应特定刺激时，HK 被激活并驱动 RR 的磷酸化，RR 负责产生适应性反应。这些系统在细菌中普遍存在，并且经常受到辅助蛋白的控制。在α变形菌中，由 HK CckA、磷酸转移酶 ChpT 和 RR CtrA 组成的 TCS 广泛分布。目前，该系统及其调节蛋白的大部分信息来自于在必需微生物中进行的发现。然而，在许多物种中并非如此，并且缺乏对该 TCS 和其调节蛋白的研究。在这项研究中，我们发现 Osp，一种 RR 样蛋白，通过 CtrA 激活 表达，从而在负反馈环中抑制 CckA 的激酶活性。Osp 的抑制作用和先前报道的 FixT 蛋白的类似作用表明，存在一组新的 RR 样蛋白，其主要功能是与 HK 相互作用并阻止其磷酸化。
