Clp proteases
including ClpA act as molecular chaperones with a similar function as DnaK/DnaJ (Wickner et al., 1994). It is likely that the up-regulation of DnaJ-class molecular chaperone in CSM2 mutant is due to the substitution of the partial Clp protease function by DnaJ when Clp protease is dysfunctional. Further, our metabolomic analysis of the Clp protease mutant identified down-regulation of amino acid and oligosaccharide transporters that are part of ABC transporter pathways (Table 2). The mechanism is likely to be similar to that observed in Mycobacterium tuberculosis under hypoxia, where Clp proteases degrade the factors that inhibit DNA replication and transcription to initiate the synthesis of amino acids during stressful conditions (Sherrid et al., 2010). Changes in the levels of TCA cycle enzymes in response to copper identified by the metabolomic analysis (Table 2) were confirmed by the PF-562271 price proteomic analysis with up-regulation of ketol-acid reductoisomerase, which participates
in the production of CoA (Table 1). In addition, down-regulation of MalR, a transcriptional regulatory protein for malate and citrate metabolism (Table 1) under copper stress would result in the accumulation of malate and citrate, the intermediate products in TCA cycle (Papa et al., 2009). Higher levels of malate allow the organism to cope with oxidative stress caused Dabrafenib solubility dmso by copper toxicity, by producing more NADPH, an important antioxidant (Singh et al., 2007). Citrate is a metabolite involved in the sequestration of aluminum and the increase of
citrate accumulation selleck screening library was previously shown in P. fluorescens grown under aluminum stress (Mailloux et al., 2008). Our results suggest that citrate is involved in the sequestration of copper. Based on our results, we propose a model for the response to toxic levels of copper in Pseudomonas sp. TLC6-6.5-4 (Fig. 4). High copper concentrations reduce its cell size, which decreases the amount of copper bound on the cell surface. In addition, smaller cells need less energy for maintenance under copper stress. CopA and lipoprotein mediate sequestration and efflux of copper outside the cytoplasm. Heat shock proteins including Clp protease and DnaJ-class molecular chaperone either degrade the damaged proteins or prevent their irreversible aggregation under copper stress. Furthermore, Clp protease is directly involved in copper resistance by up-regulation of amino acid transporters, proteins related to oxidative stress and proline accumulation. This organism maintains a fine metabolic balance to enable the cells to survive in environment with high copper concentration by increasing amino acid production and regulating TCA cycle. The authors gratefully thank J. Lutz and W. He for technical assistance with proteomic experiments and GC-MS analysis. We also thank R. Shaik for his help on proteomic and metabolomic data analysis. “
“Salmonella enterica serovar Typhi and Typhimurium are closely related serovars. However, S.