Feeling the Heat: The Campylobacter jejuni HrcA Transcriptional Repressor Is an Intrinsic Protein Thermosensor

Abstract

The heat-shock response, a universal protective mechanism consisting of a transcriptional reprogramming of the cellular transcriptome, results in the accumulation of proteins which counteract the deleterious effects of heat-stress on cellular polypeptides. To quickly respond to thermal stress and trigger the heat-shock response, bacteria rely on different mechanisms to detect temperature variations, which can involve nearly all classes of biological molecules. In Campylobacter jejuni the response to heat-shock is transcriptionally controlled by a regulatory circuit involving two repressors, HspR and HrcA. In the present work we show that the heat-shock repressor HrcA acts as an intrinsic protein thermometer. We report that a temperature upshift up to 42°C negatively affects HrcA DNA-binding activity to a target promoter, a condition required for de-repression of regulated genes. Furthermore, we show that this impairment of HrcA binding at 42°C is irreversible in vitro, as DNA-binding was still not restored by reversing the incubation temperature to 37°C. On the other hand, we demonstrate that the DNA-binding activity of HspR, which controls, in combination with HrcA, the transcription of chaperones’ genes, is unaffected by heat-stress up to 45°C, portraying this master repressor as a rather stable protein. Additionally, we show that HrcA binding activity is enhanced by the chaperonin GroE, upon direct protein–protein interaction. In conclusion, the results presented in this work establish HrcA as a novel example of intrinsic heat-sensing transcriptional regulator, whose DNA-binding activity is positively modulated by the GroE chaperonin.

Insights into the Orchestration of Gene Transcription Regulators in Helicobacter pylori

“…A temperature rise of a few degrees above 37 • C leads to an irreversible unfolding of HrcA, thereby, provoking a massive loss of its DNA-binding capacity and a prompt derepression of chaperone gene transcription [93]. A similar behavior has been observed in just a few other repressors governing heat-shock gene regulation in diverse bacteria species, including C. jejuni, Streptomyces albus, Yersinia, Salmonella, and in the thermophilic Geobacillus thermoglucosidasius [94][95][96][97][98][99].…”

Microbial Mechanisms of Heat Sensing

“…Similarly, studies on Chlamydia trachomatis during intracellular infection confirmed the regulation of heat shock genes by HrcA within the infected cell [49]. In Campylobacter jejuni, the DNA binding activity of HrcA is regulated by HspR and GroE proteins under heat shock conditions, which enhances its function as an intrinsic protein thermometer [50].…”

Recent Synthetic Biology Approaches for Temperature- and Light-Controlled Gene Expression in Bacterial Hosts

“…From a synthetic biology perspective, nature’s mechanisms for sensing temperature and light have provided powerful insights for designing tools to achieve conditional gene expression. At the molecular level, researchers have utilized the heat shock response mechanism to construct temperature-sensitive gene expression systems such as the temperature-sensitive dimeric repressor [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ], RNA polymerase (RNAP) [ 14 , 15 , 16 , 17 ], replication machinery [ 18 , 19 , 20 , 21 , 22 ], and oligonucleotide topology [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Photocaged [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ] or photoswitchable [ 44 , 45 ] small-molecule inducers and photocaged transcription factors [ 46 ] have been used to develop light-driven gene expression systems.…”