The environment of a cell has a profound influence on its physiology, development, and evolution. Caulobacter crescentus, a bacterial model for the study of cell cycle control and development, provides an excellent experimental system to investigate the molecular basis of environmental perception and adaptation. The goal of this proposal is to define the molecular and cellular mechanisms of how light and stress signals are integrated by a bacterium to regulate the cell envelope and cell adhesion. LOV-histidine kinases (LOV-HKs), a newly-discovered class of blue-light photosensors, are conserved across a range of prokaryotes. Although the regulatory roles of LOV- HKs are not well understood, these signaling proteins have recently been shown to control virulence in Brucella abortus and cell adhesion in Caulobacter in response to light. Prior to these discoveries, neither Caulobacter nor Brucella were known or presumed to respond to visible light. Indeed, the majority of species encoding LOV-HKs are chemotrophs with no predicted photobiology. We have uncovered a regulatory network in Caulobacter in which the LOV-HK, LovK, and the receiver protein, LovR, form a form a regulatory feedback loop with CT, an envelope stress sigma factor that is critical for cell survival under osmotic and oxidative stress. The experiments detailed in this proposal will test the hypothesis that LovK/LovR system is part of a novel signaling network in which classical two- component signaling and C-dependent control of transcription intersect to regulate the composition of the cell envelope in response to multiple physical and chemical cues in the environment. We will use a combination of methods to define how interaction between the chemical and light environments affect cellular stress adaptation, cell envelope composition, and cell adhesion. Specifically, we will answer the following questions: (i) How does the LovK/LovR two-component system regulate cell envelope composition and cell adhesion in response to light, (ii) What are the regulatory interactions between the LovK/LovR photosensory network and the CT stress-response network, and (iii) What are the transcriptional targets of CT, CU, and PhyR, three sigma factors that appear to be regulated by CT? Time permitting, we use genetic and biochemical screens to identify additional regulators in the LovK/LovR adhesion pathway. Our experiments will advance our understanding of photoregulation by LOV-HKs, an important new area of prokaryotic biology that impacts bacterial pathogenesis. More generally, these studies will provide important data on mechanisms bacteria use to sense and integrate multiple environmental stimuli in a fluctuating environment, which is critical for bacterial cell survival.

Public Health Relevance

Histidine kinases and response regulators, known commonly as two-component signaling proteins, are essential virulence factors in numerous bacterial pathogens including Staphylococcus aureus and Brucella abortus. A newly-discovered class of photosensory histidine kinases, known as the LOV- HKs, regulate virulence in Brucella abortus and cell adhesion in Caulobacter crescentus in response to visible light. Our proposed research on LOV-HK regulation of cell physiology using the powerful Caulobacter model system promises to provide insight into new modes of photoregulation in bacteria, including the molecular and cellular basis of light-mediated virulence in the class III pathogen Brucella.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM087353-04
Application #
8269705
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Reddy, Michael K
Project Start
2009-08-01
Project End
2014-05-31
Budget Start
2012-06-01
Budget End
2013-05-31
Support Year
4
Fiscal Year
2012
Total Cost
$304,795
Indirect Cost
$103,874
Name
University of Chicago
Department
Biochemistry
Type
Schools of Medicine
DUNS #
005421136
City
Chicago
State
IL
Country
United States
Zip Code
60637
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Herrou, Julien; Rotskoff, Grant; Luo, Yun et al. (2012) Structural basis of a protein partner switch that regulates the general stress response of ýý-proteobacteria. Proc Natl Acad Sci U S A 109:E1415-23
Foreman, Robert; Fiebig, Aretha; Crosson, Sean (2012) The LovK-LovR two-component system is a regulator of the general stress pathway in Caulobacter crescentus. J Bacteriol 194:3038-49
Herrou, Julien; Foreman, Robert; Fiebig, Aretha et al. (2010) A structural model of anti-anti-ýý inhibition by a two-component receiver domain: the PhyR stress response regulator. Mol Microbiol 78:290-304
Alexandre, Maxime T A; Purcell, Erin B; van Grondelle, Rienk et al. (2010) Electronic and protein structural dynamics of a photosensory histidine kinase. Biochemistry 49:4752-9
Purcell, Erin B; McDonald, Claudia A; Palfey, Bruce A et al. (2010) An analysis of the solution structure and signaling mechanism of LovK, a sensor histidine kinase integrating light and redox signals. Biochemistry 49:6761-70