title: DnaK-sigma 32 interaction is temperature-dependent. Implication for the mechanism of heat shock response.
abstract: The heat shock response in bacteria is a complex phenomenon in which sigma 32 plays the central role. The DnaK/J chaperone system binds and promotes degradation of sigma 32 at lower temperatures. At heat shock temperatures, the DnaK/J-mediated degradation of sigma 32 is largely abolished by a mechanism, which is not yet fully understood. In this article we have shown that interaction of DnaK with sigma 32 is highly temperature-dependent. This interaction is completely abolished at 42 degrees C. To investigate the origin of such strong temperature dependence, we have monitored the structural changes that occur in the sigma 32 protein upon upshift of temperature and attempted to elucidate its functional roles. Upon a shift of temperature from 30 to 42 degrees C, the CD spectrum of sigma 32 becomes significantly more positive without significant change in either tryptophan fluorescence spectra or quenchability to external quenchers. 1,8-Anilinonaphthalene sulfonic acid binding at 42 degrees C is not significantly affected. The equilibrium guanidine hydrochloride denaturation of sigma 32 is biphasic. The first phase shifts to even lower guanidine hydrochloride concentrations at 42 degrees C, whereas the major phase remains largely unchanged. The sigma 32-core interaction remains unchanged as a function of temperature. This suggests that increased temperature destabilizes a structural element. We discuss the possible location of this temperature-sensitive structural element.
authors.affiliation: Department of Biophysics, Bose Institute, P-1/12, C.I.T. Scheme VII M, Calcutta 700 054, India.
authors.forename: Ruchira
authors.initials: R
authors.lastname: Chattopadhyay
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Roy
mesh_terms: D000595:Amino Acid Sequence; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism; D006358:Hot Temperature; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011489:Protein Denaturation; D012808:Sigma Factor; D013696:Temperature; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C063842:dnaK protein, E coli