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Crystal structure of a functional dimer of the PhoQ sensor domain.

Cheung J, Bingman CA, Reyngold M, Hendrickson WA, Waldburger CD - J. Biol. Chem. (2008)

Bottom Line: Analysis of the wild-type structure reveals a dimer that allows for the formation of a salt bridge across the dimer interface between Arg-50' and Asp-179 and with nickel ions bound to aspartate residues in the acidic cluster.The physiological importance of the salt bridge to in vivo PhoQ function has been confirmed by mutagenesis.The mutant structure has an alternative, non-physiological dimeric association.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, New York 10032, USA.

ABSTRACT
The PhoP-PhoQ two-component system is a well studied bacterial signaling system that regulates virulence and stress response. Catalytic activity of the histidine kinase sensor protein PhoQ is activated by low extracellular concentrations of divalent cations such as Mg2+, and subsequently the response regulator PhoP is activated in turn through a classic phosphotransfer pathway that is typical in such systems. The PhoQ sensor domains of enteric bacteria contain an acidic cluster of residues (EDDDDAE) that has been implicated in direct binding to divalent cations. We have determined crystal structures of the wild-type Escherichia coli PhoQ periplasmic sensor domain and of a mutant variant in which the acidic cluster was neutralized to conservative uncharged residues (QNNNNAQ). The PhoQ domain structure is similar to that of DcuS and CitA sensor domains, and this PhoQ-DcuS-CitA (PDC) sensor fold is seen to be distinct from the superficially similar PAS domain fold. Analysis of the wild-type structure reveals a dimer that allows for the formation of a salt bridge across the dimer interface between Arg-50' and Asp-179 and with nickel ions bound to aspartate residues in the acidic cluster. The physiological importance of the salt bridge to in vivo PhoQ function has been confirmed by mutagenesis. The mutant structure has an alternative, non-physiological dimeric association.

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Structure of an acid mutant PhoQ 43–190 subunit. A, the overall structure of the acid mutant PhoQ 43–190 (molecule A) is shown as a ribbon diagram with secondary structure elements labeled in black. B, a stereo plot of the Cα trace of the same acid mutant PhoQ 43–190 molecule. Every tenth Cα atom is depicted as a black sphere and labeled accordingly. The diagrams were created using MolScript (43) and BobScript (44).
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fig2: Structure of an acid mutant PhoQ 43–190 subunit. A, the overall structure of the acid mutant PhoQ 43–190 (molecule A) is shown as a ribbon diagram with secondary structure elements labeled in black. B, a stereo plot of the Cα trace of the same acid mutant PhoQ 43–190 molecule. Every tenth Cα atom is depicted as a black sphere and labeled accordingly. The diagrams were created using MolScript (43) and BobScript (44).

Mentions: The structure of acidic cluster mutant PhoQ 43–190 (Fig. 2) was determined by molecular replacement starting from a partial model of wild-type PhoQ 43–190. Two molecules were found in the asymmetric unit in space group P41. As for the wild-type structure, these molecules are related by a quasi-diad axis of symmetry, but the arrangement is very different in this case (see below). Residues at positions 43–188 and 45–190 of molecule A and B, respectively, were found to be ordered. A total of 292 residues, 336 water molecules, and 1 sulfate ion was refined to R and Rfree values of 16.8% and 23.0%, respectively, at a resolution of 2.0 Å against data collected from a single native crystal (Tables 1 and 2).


Crystal structure of a functional dimer of the PhoQ sensor domain.

Cheung J, Bingman CA, Reyngold M, Hendrickson WA, Waldburger CD - J. Biol. Chem. (2008)

Structure of an acid mutant PhoQ 43–190 subunit. A, the overall structure of the acid mutant PhoQ 43–190 (molecule A) is shown as a ribbon diagram with secondary structure elements labeled in black. B, a stereo plot of the Cα trace of the same acid mutant PhoQ 43–190 molecule. Every tenth Cα atom is depicted as a black sphere and labeled accordingly. The diagrams were created using MolScript (43) and BobScript (44).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2376233&req=5

fig2: Structure of an acid mutant PhoQ 43–190 subunit. A, the overall structure of the acid mutant PhoQ 43–190 (molecule A) is shown as a ribbon diagram with secondary structure elements labeled in black. B, a stereo plot of the Cα trace of the same acid mutant PhoQ 43–190 molecule. Every tenth Cα atom is depicted as a black sphere and labeled accordingly. The diagrams were created using MolScript (43) and BobScript (44).
Mentions: The structure of acidic cluster mutant PhoQ 43–190 (Fig. 2) was determined by molecular replacement starting from a partial model of wild-type PhoQ 43–190. Two molecules were found in the asymmetric unit in space group P41. As for the wild-type structure, these molecules are related by a quasi-diad axis of symmetry, but the arrangement is very different in this case (see below). Residues at positions 43–188 and 45–190 of molecule A and B, respectively, were found to be ordered. A total of 292 residues, 336 water molecules, and 1 sulfate ion was refined to R and Rfree values of 16.8% and 23.0%, respectively, at a resolution of 2.0 Å against data collected from a single native crystal (Tables 1 and 2).

Bottom Line: Analysis of the wild-type structure reveals a dimer that allows for the formation of a salt bridge across the dimer interface between Arg-50' and Asp-179 and with nickel ions bound to aspartate residues in the acidic cluster.The physiological importance of the salt bridge to in vivo PhoQ function has been confirmed by mutagenesis.The mutant structure has an alternative, non-physiological dimeric association.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, New York 10032, USA.

ABSTRACT
The PhoP-PhoQ two-component system is a well studied bacterial signaling system that regulates virulence and stress response. Catalytic activity of the histidine kinase sensor protein PhoQ is activated by low extracellular concentrations of divalent cations such as Mg2+, and subsequently the response regulator PhoP is activated in turn through a classic phosphotransfer pathway that is typical in such systems. The PhoQ sensor domains of enteric bacteria contain an acidic cluster of residues (EDDDDAE) that has been implicated in direct binding to divalent cations. We have determined crystal structures of the wild-type Escherichia coli PhoQ periplasmic sensor domain and of a mutant variant in which the acidic cluster was neutralized to conservative uncharged residues (QNNNNAQ). The PhoQ domain structure is similar to that of DcuS and CitA sensor domains, and this PhoQ-DcuS-CitA (PDC) sensor fold is seen to be distinct from the superficially similar PAS domain fold. Analysis of the wild-type structure reveals a dimer that allows for the formation of a salt bridge across the dimer interface between Arg-50' and Asp-179 and with nickel ions bound to aspartate residues in the acidic cluster. The physiological importance of the salt bridge to in vivo PhoQ function has been confirmed by mutagenesis. The mutant structure has an alternative, non-physiological dimeric association.

Show MeSH
Related in: MedlinePlus