Department of Biology I, Microbiology, Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Martinsried, Germany.
Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany.
Microbiologyopen. 2017 Jun;6(3). doi: 10.1002/mbo3.438. Epub 2017 Jan 17.
Two-component signal transduction constitutes the predominant strategy used by bacteria to adapt to fluctuating environments. The KdpD/KdpE system is one of the most widespread, and is crucial for K homeostasis. In Escherichia coli, the histidine kinase KdpD senses K availability, whereas the response regulator KdpE activates synthesis of the high-affinity K uptake system KdpFABC. Here we show that, in the absence of KdpD, kdpFABC expression can be activated via phosphorylation of KdpE by the histidine kinase PhoR. PhoR and its cognate response regulator PhoB comprise a phosphate-responsive two-component system, which senses phosphate limitation indirectly through the phosphate transporter PstCAB and its accessory protein PhoU. In vivo two-hybrid interaction studies based on the bacterial adenylate cyclase reveal pairwise interactions between KdpD, PhoR, and PhoU. Finally, we demonstrate that cross-regulation between the kdpFABC and pstSCAB operons occurs in both directions under simultaneous K and phosphate limitation, both in vitro and in vivo. This study for the first time demonstrates direct coupling between intracellular K and phosphate homeostasis and provides a mechanism for fine-tuning of the balance between positively and negatively charged ions in the bacterial cell.
双组分信号转导是细菌适应波动环境的主要策略。KdpD/KdpE 系统是最广泛的系统之一，对 K 稳态至关重要。在大肠杆菌中，组氨酸激酶 KdpD 感知 K 的可用性，而响应调节剂 KdpE 激活高亲和力 K 摄取系统 KdpFABC 的合成。在这里，我们表明，在没有 KdpD 的情况下，磷酸化 KdpE 可以通过组氨酸激酶 PhoR 激活 kdpFABC 的表达。PhoR 和其同源响应调节剂 PhoB 组成一个磷酸响应的双组分系统，通过磷酸转运蛋白 PstCAB 及其辅助蛋白 PhoU 间接感知磷酸缺乏。基于细菌腺苷酸环化酶的体内双杂交相互作用研究揭示了 KdpD、PhoR 和 PhoU 之间的两两相互作用。最后，我们证明在 K 和磷酸盐同时限制的情况下，kdpFABC 和 pstSCAB 操纵子之间的交叉调节在体外和体内都以双向方式发生。这项研究首次证明了细胞内 K 和磷酸盐稳态之间的直接偶联，并为细菌细胞中正负离子平衡的精细调节提供了一种机制。
