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BIOLOGICAL SCIENCES / MICROBIOLOGY
Escherichia coli enzyme IIA^Ntr regulates the K⁺ transporter TrkA

Chang-Ro Lee^*, Seung-Hyon Cho^*, Mi-Jeong Yoon^*, Alan Peterkofsky, and Yeong-Jae Seok^*,

*Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; and Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892

Edited by Rowena G. Matthews, University of Michigan, Ann Arbor, MI, and approved December 13, 2006 (received for review November 8, 2006)

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.

leucine toxicity | nitrogen-metabolic phosphotransferase system (PTS) | potassium transporter TrkA | protein–protein interaction | signal transduction

Author contributions: C.-R.L., M.-J.Y., A.P., and Y.-J.S. designed research; C.-R.L., S.-H.C., and Y.-J.S. performed research; C.-R.L., S.-H.C., and M.-J.Y. contributed new reagents/analytic tools; C.-R.L., S.-H.C., A.P., and Y.-J.S. analyzed data; and C.-R.L., A.P., and Y.-J.S. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS direct submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0609897104/DC1.

To whom correspondence should be addressed. E-mail: yjseok{at}plaza.snu.ac.kr

© 2007 by The National Academy of Sciences of the USA

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