Regulation and localisation of PSP proteins in E-Coli

Abstract

The phage shock protein (Psp) response is found in many Gram-negative enterobacteria, where it helps to maintain the proton motive force (PMF) when the integrity of the inner membrane (IM) is impaired and promotes virulence of pathogens such as Yersinia or Salmonella. In Escherichia coli, Psp comprises seven genes (pspF pspABCDE and pspG) which are organised in a regulon under the control of two Sigma54-dependent promoters. Despite considerable advances, neither the mechanism of Psp induction nor the functioning of the Psp response is fully understood. Recent findings comparing the roles of ArcB in Yersinia enterocolitica and E. coli caused a dispute over the requirement of the twocomponent system ArcAB in Psp signal-transduction. The present study now establishes that ArcAB involvement is conditional and appears to be mediated via protein-protein interactions between ArcB and PspB. The study further suggests that the cellular ubiquinone pool, which acts upstream of ArcAB, may also play a role in Psp signalling whereas dissipation of proton motive force (PMF), generally inferred to be the inducing signal, is not sufficient to mount a Psp response. To gain further insight into its functioning, PspA (a negative regulator and effector of Psp) and PspG (an effector of Psp) were visualised in vivo using fusions to Green fluorescent protein (GFP). To maintain PMF, PspA was proposed to uniformly cover the cytoplasmic face of the IM. However, the present study demonstrates that PspA (and PspG) is highly organised into distinct complexes at the cell pole and the lateral cell membrane. Real-time observations revealed lateral PspA and PspG complexes are highly mobile, but absent in cells lacking MreB. Without the MreB cytoskeleton, induction of the Psp response is still observed, yet these cells fail to maintain PMF under stress conditions.