Acidic pH and divalent cation sensing by PhoQ are dispensable for systemic salmonellae virulence

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Abstract

Salmonellae PhoQ is a histidine kinase with a periplasmic sensor domain (PD) that promotes virulence by detecting the macrophage phagosome. PhoQ activity is repressed by divalent cations and induced in environments of acidic pH, limited divalent cations, and cationic antimicrobial peptides (CAMP). Previously, it was unclear which signals are sensed by salmonellae to promote PhoQ-mediated virulence. We defined conformational changes produced in the PhoQ PD on exposure to acidic pH that indicate structural flexibility is induced in α-helices 4 and 5, suggesting this region contributes to pH sensing. Therefore, we engineered a disulfide bond between W104C and A128C in the PhoQ PD that restrains conformational flexibility in α-helices 4 and 5. PhoQ^W104C-A128C is responsive to CAMP, but is inhibited for activation by acidic pH and divalent cation limitation. phoQ^W104C-A128C Salmonella enterica Typhimurium are virulent in mice, indicating that acidic pH and divalent cation sensing by PhoQ are dispensable for virulence.

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Kevin G Hicks

Department of Microbiology, University of Washington Medical School, Seattle, United States

Competing interests
The authors declare that no competing interests exist.
Scott Delbecq

Department of Biochemistry, University of Washington Medical School, Seattle, United States

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The authors declare that no competing interests exist.
Enea Sancho-Vaello

Unidad de Biofísica, Centro Mixto Consejo Superior de Investigaciones Científicas, Universidad del País Vasco/Euskal Herriko Unibertsitatea, Bizkaia, Spain

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The authors declare that no competing interests exist.
Marie-Pierre Blanc

Department of Microbiology, University of Washington Medical School, Seattle, United States

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The authors declare that no competing interests exist.
Katja K Dove

Department of Biochemistry, University of Washington Medical School, Seattle, United States

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The authors declare that no competing interests exist.
Lynne R Prost

Department of Biochemistry, University of Wisconsin-Madison, Madison, United States

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The authors declare that no competing interests exist.
Margaret E Daley

Department of Chemistry and Biochemistry, University of San Diego, San Diego, United States

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The authors declare that no competing interests exist.
Kornelius Zeth

Department of Protein Evolution, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany

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The authors declare that no competing interests exist.
Rachel E Klevit

Department of Biochemistry, University of Washington Medical School, Seattle, United States

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The authors declare that no competing interests exist.
Samuel I Miller

Department of Microbiology, University of Washington Medical School, Seattle, United States

For correspondence
millersi@uw.edu

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The authors declare that no competing interests exist.

Ethics

Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocol (2982-02) of the University of Washington.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.