title: Identification of a helix-turn-helix motif of Bacillus thermoglucosidasius HrcA essential for binding to the CIRCE element and thermostability of the HrcA-CIRCE complex, indicating a role as a thermosensor.
abstract: In the heat shock response of bacillary cells, HrcA repressor proteins negatively control the expression of the major heat shock genes, the groE and dnaK operons, by binding the CIRCE (controlling inverted repeat of chaperone expression) element. Studies on two critical but yet unresolved issues related to the structure and function of HrcA were performed using mainly the HrcA from the obligate thermophile Bacillus thermoglucosidasius KP1006. These two critical issues are (i) identifying the region at which HrcA binds to the CIRCE element and (ii) determining whether HrcA can play the role of a thermosensor. We identified the position of a helix-turn-helix (HTH) motif in B. thermoglucosidasius HrcA, which is typical of DNA-binding proteins, and indicated that two residues in the HTH motif are crucial for the binding of HrcA to the CIRCE element. Furthermore, we compared the thermostabilities of the HrcA-CIRCE complexes derived from Bacillus subtilis and B. thermoglucosidasius, which grow at vastly different ranges of temperature. The thermostability profiles of their HrcA-CIRCE complexes were quite consistent with the difference in the growth temperatures of B. thermoglucosidasius and B. subtilis and, thus, suggested that HrcA can function as a thermosensor to detect temperature changes in cells.
authors.affiliation: Department of Applied Biochemistry, Kyoto Prefectural University, Shimogamo, Sakyo, Kyoto 606-8522, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Hitomi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishimura
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsujimoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsui
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018833:Chaperonins; D004269:DNA, Bacterial / Q000378:metabolism*; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D018869:Heat-Shock Response; D019077:Helix-Turn-Helix Motifs; D008969:Molecular Sequence Data; D011489:Protein Denaturation; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C028715:GroE protein, E coli; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012097:Repressor Proteins; D018833:Chaperonins; C063842:dnaK protein, E coli