title: Revisiting regulation of potassium homeostasis in Escherichia coli: the connection to phosphate limitation.
abstract: 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.
authors.affiliation: Department of Biology I, Microbiology, Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Martinsried, Germany.
authors.forename: Hannah
authors.initials: H
authors.lastname: Schramke
authors.affiliation: Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany.
authors.forename: Vera
authors.initials: V
authors.lastname: Laermann
authors.affiliation: Centrum für Biotechnologie, Universität Bielefeld, Bielefeld, Germany.|Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.|Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Halina E
authors.initials: HE
authors.lastname: Tegetmeyer
authors.affiliation: Department of Biology I, Genetics, Ludwig-Maximilians-Universität München, Martinsried, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Brachmann
authors.affiliation: Department of Biology I, Microbiology, Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Martinsried, Germany.
authors.forename: Kirsten
authors.identifier: 0000-0003-0779-6841
authors.initials: K
authors.lastname: Jung
authors.affiliation: Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany.
authors.forename: Karlheinz
authors.initials: K
authors.lastname: Altendorf
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006706:Homeostasis; D010710:Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism*; D025941:Protein Interaction Mapping; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D015534:Trans-Activators / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D010710:Phosphates; D015534:Trans-Activators; C075615:kdpE protein, E coli; C061279:PhoR protein, Bacteria; C489580:KdpD protein, E coli; D011494:Protein Kinases; D011188:Potassium
keywords: cross-regulation; histidine kinase; ion homeostasis; response regulator; signal transduction