Genetic and phenotypic characterization of the heat shock response in Pseudomonas putida.
Bottom Line: Molecular chaperones function in various important physiological processes.Null mutants of genes for the molecular chaperone ClpB (Hsp104), and those that encode J-domain proteins (DnaJ, CbpA, and DjlA), which may act as Hsp40 co-chaperones of DnaK (Hsp70), were constructed from Pseudomonas putida KT2442 (KT) to elucidate their roles.P. putida CbpA, a probable Hsp, partially substituted the functions of DnaJ in cell growth and solubilization of thermo-mediated protein aggregates, and might be involved in the HSR which was regulated by a fine-tuning system(s) that could sense subtle changes in the ambient temperature and control the levels of σ(32) activity and quantity, as well as the mRNA levels of hsp genes.
Affiliation: Graduate School of Life Sciences, Toyo University, Gunma.Show MeSH
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Mentions: The heat shock response (HSR) is a universal cellular response against damage to protein folding under heat and other stresses (Fig. 1). In many proteobacteria, the HSR is controlled by an alternative sigma factor, σ32, which directs RNA polymerase to the promoters of hsp genes (Straus et al. 1987; Morita et al. 2000; Guisbert et al. 2008). The E. coli σ32 regulon consists of about 50 transcriptional units and comprises approximately 90 genes (Nonaka et al. 2006). The regulon encodes many global transcriptional regulators and proteins that contribute to the maintenance of DNA and RNA integrity, along with canonical Hsps. The transient induction of σ32 upon heat shock, peaking at 5−15 min, is conducted by its temporal stabilization and translational upregulation (Guisbert et al. 2008). In the absence of stressors or when cells have adapted to stress conditions (shut-off stage), the level of E. coli σ32 declines through degradation by a membrane-bound ATP-dependent protease, FtsH (Herman et al. 1995; Tomoyasu et al. 1995; Tatsuta et al. 1998). Two major chaperone systems, DnaK/DnaJ/GrpE and GroEL (Hsp60)/GroES (Hsp10) are known to control the activity and quantity of σ32, thereby controlling the HSR via negative feedback loops (Guisbert et al. 2008). DnaK and GroEL are major ubiquitous chaperones that play crucial roles in promoting protein folding, not only under stress conditions but also during normal growth (Hartl et al. 2011). The DnaK system also functions in the disaggregation of thermo-mediated protein aggregates, in cooperation with ClpB (Hsp104) (Parsell et al. 1994; Glover and Lindquist 1998; Mogk et al. 1999; Tomoyasu et al. 2001; Doyle and Wickner 2009; Tyedmers et al. 2010; Seyffer et al. 2012). Protein disaggregation is considered to be initiated by the association of DnaK/DnaJ with the aggregate (Weibezahn et al. 2004), which allows binding of ClpB to the aggregate (Acebrón et al. 2009) and threading activity to be exerted (Schlieker et al. 2004). E. coli ClpB also functions in protecting cells from lethal effects of very high temperatures (Squires et al. 1991).
Affiliation: Graduate School of Life Sciences, Toyo University, Gunma.