| Primary Identifier | IPR005104 | Type | Domain |
| Short Name | WHTH_HrcA_DNA-bd |
| description | Prokaryotic cells have a defence mechanism against a sudden heat-shock stress. Commonly, they induce a set of proteins that protect cellular proteins from being denatured by heat. Among such proteins are the GroE and DnaK chaperones whose transcription is regulated by a heat-shock repressor protein HrcA. HrcA is a winged helix-turn-helix repressor that negatively regulates the transcription of dnaK and groE operons by binding the upstream CIRCE (controlling inverted repeat of chaperone expression) element. In Bacillus subtilis this element is a perfect 9 base pair inverted repeat separated by a 9 base pair spacer. The crystal structure of a heat-inducible transcriptional repressor, HrcA, from Thermotoga maritima has been reported at 2.2A resolution. HrcA is composed of three domains: an N-terminal winged helix-turn-helix domain (WHTH), a GAF-like domain, and an inserted dimerizing domain (IDD). The IDD shows a unique structural fold with an anti-parallel β-sheet composed of three β-strands sided by four α-helices. HrcA crystallises as a dimer, which is formed through hydrophobic contact between the IDDs and a limited contact that involves conserved residues between the GAF-like domains []. The structural studies suggest that the inactive form of HrcA is the dimer and this is converted to its DNA-binding form by interaction with GroEL, which binds to a conserved C-terminal sequence region [, ]. Comparison of the HrcA-CIRCE complexes from B. subtilis and Bacillus thermoglucosidasius (Geobacillus thermoglucosidasius), which grow at vastly different ranges of temperature shows that the thermostability profiles were consistent with the difference in the growth temperatures suggesting that HrcA can function as a thermosensor to detect temperature changes in cells []. Any increase in temperature causes the dissociation of the HrcA from the CIRCE complex with the concomitant activation of transcription of the groE and dnaK operons. This domain represents the winged helix-turn-helix DNA-binding domain which is located close to the N terminus of HrcA. This domain is also found at the N terminus of a set of uncharacterised proteins that have two C-terminal CBS domains. |
