Abstract
The phage shock protein (Psp) F regulon response in Escherichia coli is thought to be induced by impaired inner membrane integrity and an associated decrease in proton motive force (pmf). Mechanisms by which the Psp system detects the stress signal and responds have so far remained undetermined. Here we demonstrate that PspA and PspG directly confront a variety of inducing stimuli by switching the cell to anaerobic respiration and fermentation and by down-regulating motility, thereby subtly adjusting and maintaining energy usage and pmf. Additionally, PspG controls iron usage. We show that the Psp-inducing protein IV secretin stress, in the absence of Psp proteins, decreases the pmf in an ArcB-dependent manner and that ArcB is required for amplifying and transducing the stress signal to the PspF regulon. The requirement of the ArcB signal transduction protein for induction of psp provides clear evidence for a direct link between the physiological redox state of the cell, the electron transport chain, and induction of the Psp response. Under normal growth conditions PspA and PspD control the level of activity of ArcB/ArcA system that senses the redox/metabolic state of the cell, whereas under stress conditions PspA, PspD, and PspG deliver their effector functions at least in part by activating ArcB/ArcA through positive feedback.
Highlights
Transcription of the PspF regulon in Escherichia coli, which consists of the pspABCDE operon and pspG gene, is driven by DNA-dependent RNA polymerase containing the alternative factor, 54
Strategy for Experimental Design and Transcriptome Data Analysis—Previous results demonstrated that the transcriptome response of the PspF regulon after induction by protein IV (pIV) secretin overproduction is largely limited to the members of the PspF regulon [6], suggesting a fine-tuning adaptation of the cell to stress growth conditions
Several lines of evidence show for the first time the nature of the pIV secretin phage shock protein (Psp)-inducing stimulus and reveal that ArcB is required, most likely as a redox sensor, to transduce the inducing signal to Psp (Fig. 2)
Summary
Transcription of the PspF regulon in Escherichia coli, which consists of the pspABCDE operon and pspG gene, is driven by DNA-dependent RNA polymerase containing the alternative factor, 54 (for review, see Refs. 1 and 2). The enhancer-binding protein PspF activates Psp expression (for review, see Ref. 1). In E. coli, PspB and PspC are absolutely required for the expression of the PspF regulon when induced with a secretin In E. coli PspF is a cytoplasmic protein, PspA is a peripheral inner membrane protein and resembles a coiled coil protein, PspB, PspC, and PspD are inner membrane proteins containing putative leucine zipper motifs, PspE is periplasmic, and PspG is predicted to be an integral inner membrane protein (Ref. 8 and for reviews, see Ref. 1 and 2). Under Psp inducing conditions, the interaction between PspA and PspF is disrupted, allowing activation of the pspA-E and pspG promoters (for review, see Ref. 2). Strain XL1-Blue MC4100psp JWK5716 JWK5536 JWK3882 JWK2226 JW5536 MG1655 MG1655⌬pspA MG1655⌬pspBC MG1655⌬pspD MG1655⌬pspF MVA40 MVA42 MVA47 MVA59 MVA61 MVA69 MVA27 MVA44 MVA45 tetr MC4100 (pspA-lac) (ampr)
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