Abstract
The phage shock protein (Psp) system found in enterobacteria is induced in response to impaired inner membrane integrity (where the Psp response is thought to help maintain the proton motive force of the cell) and is implicated in the virulence of pathogens such as Yersinia and Salmonella. We provided evidence that the two-component ArcAB system was involved in induction of the Psp response in Escherichia coli and now report that role of ArcAB is conditional. ArcAB, predominantly through the action of ArcA regulated genes, but also via a direct ArcB–Psp interaction, is required to propagate the protein IV (pIV)-dependent psp-inducing signal(s) during microaerobiosis, but not during aerobiosis or anaerobiosis. We show that ArcB directly interacts with the PspB, possibly by means of the PspB leucine zipper motif, thereby allowing cross-communication between the two systems. In addition we demonstrate that the pIV-dependent induction of psp expression in anaerobiosis is independent of PspBC, establishing that PspA and PspF can function as a minimal Psp system responsive to inner membrane stress.
Highlights
Bacteria in their native habitats encounter a plethora of stresses, which challenge their cellular integrity
We observed that ArcB is required for full protein IV-dependent psp expression in E. coli and proposed that psp-inducing stresses that dissipate pmf may activate ArcB (Jovanovic et al, 2006)
We found that psp induction is dependent on ArcAB only in microaerobiosis and on PspBC in microaerobiosis and aerobiosis (Fig. 1)
Summary
Bacteria in their native habitats encounter a plethora of stresses, which challenge their cellular integrity. We observed that ArcB (the sensor kinase of the two-component ArcAB system) is required for full protein IV (pIV)-dependent psp expression in E. coli and proposed that psp-inducing stresses that dissipate pmf may activate ArcB (Jovanovic et al, 2006). The ArcAB system regulates the transition from aerobic to anaerobic respiration and fermentation (reviewed by Malpica et al, 2006) where ArcB has been shown to sense the redox state of the cell through changes in the ubiquinone : ubiquinol (UQ : UQH2) ratio (see Fig. 2A and B) (Georgellis et al, 2001; Malpica et al, 2004). Increased levels of UQH2 attenuate inhibition on ArcB kinase activity imposed by UQ, enabling ArcB to phosphorylate ArcA (the response regulator). The ArcAB system is known to be of particular importance under microaerobic growth conditions, where oxygen is limiting rather than being completely absent (Alexeeva et al, 2003)
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