title: Mg2+ sensing by the Mg2+ sensor PhoQ of Salmonella enterica.
abstract: The PhoP/PhoQ two-component regulatory system governs the adaptation to low Mg(2+) environments and virulence in several Gram-negative species. During growth in low Mg(2+), the sensor PhoQ modifies the activity of the response regulator PhoP promoting gene transcription, whereas growth in high Mg(2+) represses transcription of PhoP-activated genes. The PhoQ protein harbors a periplasmic domain of 146 amino acid residues that binds Mg(2+) in vitro and is required for Mg(2+)-mediated repression in vivo. Here, we identify periplasmic mutants of the Salmonella PhoQ protein that allow transcription of PhoP-activated genes even under high Mg(2+) concentrations. When expressed in a strain harboring a PhoP variant that is phosphorylated from acetyl phosphate, some of the mutants failed to repress PhoP-promoted transcription in high Mg(2+), whereas others displayed a wild-type ability to do so. Mutant PhoQ proteins that allowed expression of PhoP-activated genes in high Mg(2+) displayed a pattern of iron-mediated cleavage in vitro that was different from that displayed by wild-type PhoQ, indicative of altered Mg(2+) binding. A PhoQ protein with the conserved histidine residue (H277) substituted by alanine could not promote transcription of PhoP-activated genes in low Mg(2+) but could turn off expression in response to high Mg(2+). Our studies demonstrate that residues G93, W97, H120 and T156 are required for a wild-type response to Mg(2+), and suggest that Mg(2+) binding to the periplasmic domain regulates several activities in the PhoQ protein.
authors.affiliation: Department of Molecular Microbiology, Howard Hughes Medical Institute, Washington University School of Medicine, 660 S. Euclid Avenue, Campus Box 8230, St. Louis, MO 63110-1093, USA.
authors.forename: Sangpen
authors.initials: S
authors.lastname: Chamnongpol
authors.forename: Michael
authors.initials: M
authors.lastname: Cromie
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Groisman
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000235:genetics; D008274:Magnesium / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019779:Salmonella enterica / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C079792:PhoQ protein, Bacteria; D011994:Recombinant Proteins; D008274:Magnesium