title: A chaperone network controls the heat shock response in E. coli.
abstract: The heat shock response controls levels of chaperones and proteases to ensure a proper cellular environment for protein folding. In Escherichia coli, this response is mediated by the bacterial-specific transcription factor, sigma32. The DnaK chaperone machine regulates both the amount and activity of sigma32, thereby coupling sigma32 function to the cellular protein folding state. In this manuscript, we analyze the ability of other major chaperones in E. coli to regulate sigma32, and we demonstrate that the GroEL/S chaperonin is an additional regulator of sigma32. We show that increasing the level of GroEL/S leads to a decrease in sigma32 activity in vivo and this effect can be eliminated by co-overexpression of a GroEL/S-specific substrate. We also show that depletion of GroEL/S in vivo leads to up-regulation of sigma32 by increasing the level of sigma32. In addition, we show that changing the levels of GroEL/S during stress conditions leads to measurable changes in the heat shock response. Using purified proteins, we show that that GroEL binds to sigma32 and decreases sigma32-dependent transcription in vitro, suggesting that this regulation is direct. We discuss why using a chaperone network to regulate sigma32 results in a more sensitive and accurate detection of the protein folding environment.
authors.affiliation: Department of Biochemistry and Biophysics, Microbiology and Immunology, and Stomatology, University of California, San Francisco, San Francisco, California 94143, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Guisbert
authors.forename: Christophe
authors.initials: C
authors.lastname: Herman
authors.forename: Chi Zen
authors.initials: CZ
authors.lastname: Lu
authors.forename: Carol A
authors.initials: CA
authors.lastname: Gross
mesh_terms: D018835:Chaperonin 10 / Q000378:metabolism; D018834:Chaperonin 60 / Q000378:metabolism; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000502:physiology*; D018869:Heat-Shock Response / Q000502:physiology*; D018832:Molecular Chaperones / Q000502:physiology*; D017510:Protein Folding; D012808:Sigma Factor / Q000502:physiology*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012808:Sigma Factor; C069774:heat-shock sigma factor 32; D001616:beta-Galactosidase; C063842:dnaK protein, E coli