title: Cooperativity in signal transfer through the Uhp system of Escherichia coli.
abstract: The UhpABC regulatory system in enterobacteria controls the expression of the hexose phosphate transporter UhpT. Signaling is initiated through sensing of extracellular glucose 6-phosphate by membrane-bound UhpC, which in turn modulates the histidine-protein kinase UhpB. Together with the cytoplasmic response regulator UhpA, they constitute a typical two-component regulatory system based on His-to-Asp phosphoryl transfer. Activated (i.e., phosphorylated) UhpA binds to the promoter region of uhpT, resulting in initiation of transcription. We have investigated the contribution of transmembrane signaling (through UhpBC) and intracellular activation (through UhpA) to the overall Uhp response (UhpT expression) in vivo. UhpA activation could be made independent of transmembrane signaling when (Delta)uhpBC cells were grown on pyruvate. Inorganic phosphate interfered with glucose 6-phosphate-dependent, UhpBC-mediated, as well as pyruvate-mediated activation of UhpA. The relationship between the concentration of inducer (glucose 6-phosphate) and the Uhp induction rate was nonhyperbolic, indicating positive cooperativity. The degree of cooperativity was affected by the carbon or energy source available to the cells for growth. As pyruvate-mediated activation of UhpA in (Delta)uhpBC cells could result in considerably stronger UhpT expression than glucose 6-phosphate-dependent activation through UhpBC, the observed positive cooperativity for the overall pathway in wild-type cells may reflect the previously described cooperative binding of UhpA to the uhpT promoter (J. L. Dahl et al., J. Biol. Chem. 272:1910-1919, 1997).
authors.affiliation: Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, Faculty of Science, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Daniël T
authors.initials: DT
authors.lastname: Verhamme
authors.forename: Pieter W
authors.initials: PW
authors.lastname: Postma
authors.forename: Wim
authors.initials: W
authors.lastname: Crielaard
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Hellingwerf
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D003470:Culture Media; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D010710:Phosphates; D010766:Phosphorylation; D010770:Phosphotransferases; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D019289:Pyruvic Acid; D015398:Signal Transduction; D013403:Sugar Phosphates / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D003470:Culture Media; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D010710:Phosphates; D013403:Sugar Phosphates; C489848:UhpA protein, E coli; C063498:UhpT protein, E coli; C490131:uhpC protein, E coli; C080370:UhpA protein, Bacteria; C086586:uhpB protein, Bacteria; C086587:uhpC protein, bacteria; D019289:Pyruvic Acid; D010770:Phosphotransferases