title: The phosphatase activity is the target for Mg2+ regulation of the sensor protein PhoQ in Salmonella.
abstract: The PhoP/PhoQ two-component system controls the expression of essential virulence traits in the pathogenic bacterium Salmonella enterica serovar Typhimurium. Environmental deprivation of Mg(2+) activates the PhoP/PhoQ signal transduction cascade, which results in an increased expression of genes necessary for survival inside the host. It was previously demonstrated that the interaction of Mg(2+) with the periplasmic domain of PhoQ promotes a conformational change in the sensor protein that leads to the down-regulation of PhoP-activated genes. We have now examined the regulatory effect of Mg(2+) on the putative activities of the membrane-bound PhoQ. We demonstrated that Mg(2+) promotes a phospho-PhoP phosphatase activity in the sensor protein. This activity depends on the intactness of the conserved His-277, suggesting that the phosphatase active site overlaps the H box. The integrity of the N-terminal domain of PhoQ was essential for the induction of the phosphatase activity, because Mg(2+) did not stimulate the release of inorganic phosphate from phospho-PhoP in a fusion protein that lacks this sensing domain. These findings reveal that the sensor PhoQ harbors a phospho-PhoP phosphatase activity, and that this phosphatase activity is the target of the extracellular Mg(2+)-triggered regulation of the PhoP/PhoQ system.
authors.affiliation: Departamento de Microbiologia, Facultad de Ciencias Bioquimicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Argentina.
authors.forename: M E
authors.initials: ME
authors.lastname: Castelli
authors.forename: E
authors.initials: E
authors.lastname: García Véscovi
authors.forename: F C
authors.initials: FC
authors.lastname: Soncini
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers; D008274:Magnesium / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D019779:Salmonella enterica / Q000201:enzymology / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; C079792:PhoQ protein, Bacteria; C061064:PhoP protein, Bacteria; D010749:Phosphoprotein Phosphatases; D008274:Magnesium