Lee Chang-Ro, Cho Seung-Hyon, Yoon Mi-Jeong, Peterkofsky Alan, Seok Yeong-Jae
Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea.
Proc Natl Acad Sci U S A. 2007 Mar 6;104(10):4124-9. doi: 10.1073/pnas.0609897104. Epub 2007 Feb 8.
The maintenance of ionic homeostasis in response to changes in the environment is essential for all living cells. Although there are still many important questions concerning the role of the major monovalent cation K(+), cytoplasmic K(+) in bacteria is required for diverse processes. Here, we show that enzyme IIA(Ntr) (EIIA(Ntr)) of the nitrogen-metabolic phosphotransferase system interacts with and regulates the Escherichia coli K(+) transporter TrkA. Previously we reported that an E. coli K-12 mutant in the ptsN gene encoding EIIA(Ntr) was extremely sensitive to growth inhibition by leucine or leucine-containing peptides (LCPs). This sensitivity was due to the requirement of the dephosphorylated form of EIIA(Ntr) for the derepression of ilvBN expression. Whereas the ptsN mutant is extremely sensitive to LCPs, a ptsN trkA double mutant is as resistant as WT. Furthermore, the sensitivity of the ptsN mutant to LCPs decreases as the K(+) level in culture media is lowered. We demonstrate that dephosphorylated EIIA(Ntr), but not its phosphorylated form, forms a tight complex with TrkA that inhibits the accumulation of high intracellular concentrations of K(+). High cellular K(+) levels in a ptsN mutant promote the sensitivity of E. coli K-12 to leucine or LCPs by inhibiting both the expression of ilvBN and the activity of its gene products. Here, we delineate the similarity of regulatory mechanisms for the paralogous carbon and nitrogen phosphotransferase systems. Dephosphorylated EIIA(Glc) regulates a variety of transport systems for carbon sources, whereas dephosphorylated EIIA(Ntr) regulates the transport system for K(+), which has global effects related to nitrogen metabolism.
响应环境变化维持离子稳态对所有活细胞至关重要。尽管关于主要单价阳离子K⁺的作用仍有许多重要问题，但细菌细胞质中的K⁺参与多种过程。在此，我们表明氮代谢磷酸转移酶系统的酶IIA(Ntr)（EIIA(Ntr)）与大肠杆菌K⁺转运蛋白TrkA相互作用并对其进行调节。此前我们报道，编码EIIA(Ntr)的ptsN基因中的大肠杆菌K - 12突变体对亮氨酸或含亮氨酸肽（LCPs）的生长抑制极其敏感。这种敏感性是由于EIIA(Ntr)的去磷酸化形式是ilvBN表达去阻遏所必需的。虽然ptsN突变体对LCPs极其敏感，但ptsN trkA双突变体与野生型一样具有抗性。此外，随着培养基中K⁺水平降低，ptsN突变体对LCPs的敏感性也降低。我们证明，去磷酸化的EIIA(Ntr)而非其磷酸化形式与TrkA形成紧密复合物，抑制细胞内高浓度K⁺的积累。ptsN突变体中高细胞K⁺水平通过抑制ilvBN的表达及其基因产物的活性，增强了大肠杆菌K - 12对亮氨酸或LCPs的敏感性。在此，我们阐述了同源碳和氮磷酸转移酶系统调节机制的相似性。去磷酸化的EIIA(Glc)调节多种碳源转运系统，而去磷酸化的EIIA(Ntr)调节K⁺转运系统，这与氮代谢具有全局相关性。
