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PLoS One. 2014 Feb 28;9(2):e89671. doi: 10.1371/journal.pone.0089671. eCollection 2014.

Dynamics of an interactive network composed of a bacterial two-component system, a transporter and K+ as mediator.

Author information

  • 1Center for Integrated Protein Science Munich (CiPSM) at the Department Biology I, Microbiology, Ludwig-Maximilians-Universität München, Martinsried, Germany.
  • 2Fachgebiet für Systembiotechnologie, Technische Universität München, Garching b. München, Germany.
  • 3BioProcess Engineering Group, IIM-CSIC, Spanish Council for Scientific Research, Vigo, Spain.

Abstract

KdpD and KdpE form a histidine kinase/response regulator system that senses K(+) limitation and induces the kdpFABC operon, which encodes a high-affinity K(+) uptake complex. To define the primary stimulus perceived by KdpD we focused in this study on the dynamics of the Kdp response. Escherichia coli cells were subjected to severe K(+) limitation, and all relevant parameters of the Kdp response, i.e., levels of kdpFABC transcripts and KdpFABC proteins, as well as extra- and intracellular K(+) concentrations, were quantitatively analysed over time (0 to 180 min). Unexpectedly, induction of kdpFABC was found to follow a non-monotonic time-course. To interpret this unusual behaviour, a mathematical model that adequately captures the dynamics of the Kdp system was established and used for simulations. We found a strong correlation between KdpD/KdpE activation and the intracellular K(+) concentration, which is influenced by the uptake of K(+) via the KdpFABC complex. Based on these results a model is proposed in which KdpD/KdpE phosphorylation is inversely correlated with the intracellular K(+) concentration. To corroborate this hypothesis an isogenic mutant that produces a defective KdpFABC complex, and the trans-complemented mutant that expresses the KtrAB high-affinity K(+) uptake system of Vibrio alginolyticus were quantitatively analysed. Experimental data and simulations for the mutants consistently support the tight correlation between KdpD/KdpE activation and the intracellular K(+) concentration. This study presents a striking example of the non-intuitive dynamics of a functional unit comprising signalling proteins and a transporter with K(+) as mediator.

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