Bacteria use energy dependent proteases to respond to stressful conditions. These proteases serve a dual role: destroying aberrant, potentially toxic, damaged proteins and generating stress responsive signals through degradation of regulatory factors. Cells often arrest replication in response to stress, but how regulated proteolysis contributes to cell cycle arrest in bacteria is currently poorly understood. This proposal addresses how stress related proteases target replication factors using a combination of biochemical, genetic and proteomic approaches, specifically focusing on proteases and replication factors from the model bacteria Caulobacter crescentus.
Aims 1 and 2 determine how misfolded proteins generated during proteotoxic stress directly stimulate the Lon protease to destroy the replication initiator DnaA and cause growth arrest during stress.
Aims 3 and 4 focus on how partial processing of the clamp loader subunit DnaX by the ClpXP protease is critical for replication stress tolerance during DNA damage. Because these proteases and replication factors are highly conserved throughout all bacteria, these results will impact our general understanding of replication, proteolysis, and stress tolerance. The critical role of these proteases in bacterial virulence and pathogenicity, together with the universal requirement for these proteases in bacterial stress responses, suggests that they are excellent targets for development of new antibiotic strategies that are of immediate human health need.

Public Health Relevance

Energy dependent proteases are found in all bacteria and necessary for virulence in many human pathogens. When bacteria are stressed, such as when they invade a host or encounter antibiotics, a crucial response is to stop growing in order to repair damages before they invest limited resources in growth. By determining how these changes rely on proteolytic degradation of essential replication factors, this work will reveal new path- ways that could be targeted to block bacterial virulence or to prevent bacteria from resisting the stresses produced by currently used antibiotics.

National Institute of Health (NIH)
Research Project (R01)
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Prokaryotic Cell and Molecular Biology Study Section (PCMB)
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Reddy, Michael K
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University of Massachusetts Amherst
Schools of Arts and Sciences
United States
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Mukherjee, Sampriti; Bree, Anna C; Liu, Jing et al. (2015) Adaptor-mediated Lon proteolysis restricts Bacillus subtilis hyperflagellation. Proc Natl Acad Sci U S A 112:250-5
Liu, Jing; Chien, Peter (2014) Structure and activation of a heteromeric protease complex. Proc Natl Acad Sci U S A 111:15289-90
Smith, Stephen C; Joshi, Kamal K; Zik, Justin J et al. (2014) Cell cycle-dependent adaptor complex for ClpXP-mediated proteolysis directly integrates phosphorylation and second messenger signals. Proc Natl Acad Sci U S A 111:14229-34
Chien, Peter; Gierasch, Lila M (2014) Challenges and dreams: physics of weak interactions essential to life. Mol Biol Cell 25:3474-7