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Journal of Bacteriology, March 2001, p. 1787-1791, Vol. 183, No. 5
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.5.1787-1791.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Characterization of the Catalytic Activities of the PhoQ Histidine Protein Kinase of Salmonella enterica Serovar Typhimurium

Martin Montagne, Alexandre Martel, and Hervé Le Moual*

Department of Pharmacology, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4

Received 31 July 2000/Accepted 30 November 2000

Studies of Escherichia coli membranes that were highly enriched in the Salmonella enterica serovar Typhimurium PhoQ protein showed that the presence of ATP and divalent cations such as Mg2+, Mn2+, Ca2+, or Ba2+ resulted in PhoQ autophosphorylation. However, when Mg2+ or Mn2+ was present at concentrations higher than 0.1 mM, the kinetics of PhoQ autophosphorylation were strongly biphasic, with a rapid autophosphorylation phase followed by a slower dephosphorylation phase. A fusion protein lacking the sensory and transmembrane domains retained the autokinase activity but could not be dephosphosphorylated when Mg2+ or Mn2+ was present at high concentrations. The instability of purified [32P]phospho-PhoP in the presence of PhoQ-containing membranes indicated that PhoQ also possesses a phosphatase activity. The PhoQ phosphatase activity was stimulated by increasing the Mg2+ concentration. These data are consistent with a model in which Mg2+ binding to the sensory domain of PhoQ coordinately regulates autokinase and phosphatase activities.

* Corresponding author. Mailing address: Department of Pharmacology, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4. Phone: (819) 820-6856. Fax: (819) 564-5400. E-mail: herve.lemoual{at}courrier.usherb.ca.

Journal of Bacteriology, March 2001, p. 1787-1791, Vol. 183, No. 5
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.5.1787-1791.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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