The extension of the fourth transmembrane helix of the sensor kinase KdpD of Escherichia coli is involved in sensing
Autor(en): | Zimmann, Petra Steinbruegge, Anne Schniederberend, Maren Jung, Kirsten Altendorf, Karlheinz |
Stichwörter: | ATPASE; C-TERMINAL DOMAIN; EXPRESSION; K+; Microbiology; OPERON; OSMOTIC CONTROL; PHOSPHATASE-ACTIVITY; POTASSIUM; PROTEIN; TURGOR SENSOR | Erscheinungsdatum: | 2007 | Herausgeber: | AMER SOC MICROBIOLOGY | Journal: | JOURNAL OF BACTERIOLOGY | Volumen: | 189 | Ausgabe: | 20 | Startseite: | 7326 | Seitenende: | 7334 | Zusammenfassung: | The KdpD sensor kinase and the KdpE response regulator control expression of the kdpFABC operon coding for the KdpFABC high-affinity K+ transport system of Escherichia coli. In search of a distinct part of the input domain of KdpD which is solely responsible for K+ sensing, sequences of kdpD encoding the transmembrane region and adjacent N-terminal and C-terminal extensions were subjected to random mutagenesis. Nine KdpD derivatives were identified that had lost tight regulation of kdpFABC expression. They all carried single amino acid replacements located in a region encompassing the fourth transmembrane helix and the adjacent arginine cluster of KdpD. All mutants exhibited high levels of kdpFABC expression regardless of the external K+ concentration. However, 3- to 14-fold induction was observed under extreme K+-limiting conditions and in response to an osmotic upshift when sucrose was used as an osmollyte. These KdpD derivatives were characterized by a reduced phosphatase activity in comparison to the autokinase activity in vitro, which explains constitutive expression. Whereas for wild-type KdpD the autokinase activity and also, in turn, the phosphotransfer activity to KdpE were inhibited by increasing concentrations of K+, both activities were unaffected in the KdpD derivatives. These data clearly show that the extension of the fourth transmembrane helix encompassing the arginine cluster is mainly involved in sensing both K+ limitation and osmotic upshift, which may not be separated mechanistically. |
ISSN: | 00219193 | DOI: | 10.1128/JB.00976-07 |
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