Two-component systems are one of the primary modes of signal transduction that bacteria use to sense and respond to their environment. These circuits play a key role in enabling bacteria to adapt to diverse growth conditions, control developmental programs, and initiate pathogenic lifestyles. The prototypical two-component system consists of two-proteins, an upstream histidine kinase that is usually involved in signal detection, and a downstream response regulator, which controls the circuit output. Information flow occurs by transfer of a phosphoryl group from the histidine kinase to the response regulator. Two-component systems can deviate from this simple architecture, however, and have additional protein components or more complex phosphotransfer paths. In previous work we discovered that a small 47 amino acid membrane protein, MgrB, inhibits PhoQ activity. Since MgrB expression is activated by PhoP, the protein functions as part of a negative feedback loop in the PhoQ/PhoP circuit. PhoQ is also stimulated by SafA, another small membrane protein, whose expression is controlled by the acid-responsive EvgS/EvgA two component systems. MgrB and SafA are among a group of recently discovered small hydrophobic proteins that modulate histidine kinase function. In this proposal we will combine fluorescence microscopy to follow circuit behavior in single cells, with genetic analysis and modeling to explore the role of MgrB and SafA in PhoQ/PhoP signaling. We will determine the effect of these proteins on the dynamics and input-output behavior of PhoQ/PhoP signaling for stimulation with magnesium, antimicrobial peptides and pH, compare the behavior of the low pH response among natural E. coli isolates, characterize new input signals that modulate the PhoQ/PhoP circuit through MgrB, and study the growth defect associated with dysregulation of the MgrB-PhoQ-PhoP pathway.

Public Health Relevance

The PhoQ/PhoP regulatory circuit is a critical system for enabling bacteria such as Escherichia coli and Salmonella to colonize animal hosts and cause disease. Progress in understanding the regulation of this system by small membrane proteins, the focus of this proposal, will further our understanding of how these bacteria resist host defenses and may aid in the development of new antibiotics and compounds that specifically inhibit the virulence of these pathogens.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Cellular Signaling and Regulatory Systems Study Section (CSRS)
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Maas, Stefan
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University of Pennsylvania
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Lasaro, Melissa; Liu, Zhi; Bishar, Rima et al. (2014) Escherichia coli isolate for studying colonization of the mouse intestine and its application to two-component signaling knockouts. J Bacteriol 196:1723-32
Ram, Sri; Goulian, Mark (2013) The architecture of a prototypical bacterial signaling circuit enables a single point mutation to confer novel network properties. PLoS Genet 9:e1003706
Lippa, Andrew M; Goulian, Mark (2012) Perturbation of the oxidizing environment of the periplasm stimulates the PhoQ/PhoP system in Escherichia coli. J Bacteriol 194:1457-63
Libby, Elizabeth A; Roggiani, Manuela; Goulian, Mark (2012) Membrane protein expression triggers chromosomal locus repositioning in bacteria. Proc Natl Acad Sci U S A 109:7445-50
Siryaporn, Albert; Goulian, Mark (2010) Characterizing cross-talk in vivo avoiding pitfalls and overinterpretation. Methods Enzymol 471:1-16
Goulian, Mark (2010) Two-component signaling circuit structure and properties. Curr Opin Microbiol 13:184-9
Siryaporn, Albert; Perchuk, Barrett S; Laub, Michael T et al. (2010) Evolving a robust signal transduction pathway from weak cross-talk. Mol Syst Biol 6:452
Goldberg, Shalom D; Clinthorne, Graham D; Goulian, Mark et al. (2010) Transmembrane polar interactions are required for signaling in the Escherichia coli sensor kinase PhoQ. Proc Natl Acad Sci U S A 107:8141-6
Lippa, Andrew M; Goulian, Mark (2009) Feedback inhibition in the PhoQ/PhoP signaling system by a membrane peptide. PLoS Genet 5:e1000788
Goldberg, Shalom D; Derr, Paige; DeGrado, William F et al. (2009) Engineered single- and multi-cell chemotaxis pathways in E. coli. Mol Syst Biol 5:283

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