Panel A: cells grown at 30°C in the presence of CCCP, panel B: control cells at 30°C, and panel C: cells submitted to 50°C. The numbers in the lanes signify the time of chasing in minutes. Besides induction of hsps, protonophores were known to inhibit translocation of the membrane and periplasmic proteins, resulting in their accumulation in cell cytosol as non-functional precursor form [28–30]. In order to find out the detailed molecular correlation between protonophores-mediated induction of heat-shock-like response and inhibition of protein translocation, the inducible periplasmic protein AP of E. coli was selected here as the selleck products representative
target protein for the translocation experiments. AP was a nonspecific phosphomonoesterase, used to generate inorganic phosphate
from a variety of phosphorylated derivatives. The AP selleck screening library Saracatinib ic50 gene was known to be inducible as its expression was negatively regulated by the inorganic phosphate – the end product of AP digestion. Thus, the addition of phosphate to the growth medium repressed the induction of AP or in other words, phosphate-less growth medium induced AP in E. coli . When AP was induced in presence of the protonophores, the level of cellular active AP, at any instant of growth, had decreased gradually by the presence of increasing concentrations of CCCP (0 – 50 μM) [fig. 4A] or DNP (0 – 1.5 mM) [not shown] in the growth medium. At 50 μM CCCP concentration, the amount of enzymatically active AP was almost absent. However, the western Non-specific serine/threonine protein kinase blot study of the periplasmic, cytoplasmic and membrane fractions of cells using anti-AP antibody (fig. 4B) showed that the lane g, where the cytoplasmic fraction of the CCCP-treated cells was loaded, had contained the induced AP. No considerable AP band was observed in the lanes (f & e), where the periplasmic and membrane fractions of the CCCP-treated cells were
loaded respectively. On the other hand, in the case of CCCP-untreated control cells, approximately equal amount of AP was found to be present in both periplasmic (lane b) and cytoplasmic (lane c) fractions; no trace of AP was found in the membrane fraction (lane a). The AP in the cytoplasmic fraction of the control cells (lane c), perhaps, represented the amount of AP that had yet to be translocated to the periplasm. The result of this study revealed that by the presence of CCCP (50 μM) in the growth medium, the induced AP could not be transported out from the cytoplasm to the periplasm. The less intensity of the AP band in lane g compared to the sum of the intensities in lanes b and c implied less induction of AP in cells grown in the presence of CCCP with respect to the control cells; this was consistent with the fact of low growth rate of the CCCP-treated cells (result not shown).