Properties of the phage-shock-protein (Psp) regulatory complex that govern signal transduction and induction of the Psp response in Escherichia coli

Abstract

The phage-shock-protein (Psp) response maintains the proton-motive force (pmf) under extracytoplasmic stress conditions that impair the inner membrane (IM) in bacterial cells. In Escherichia coli transcription of the pspABCDE and pspG genes requires activation of σ54-RNA polymerase by the enhancer-binding protein PspF. A regulatory network comprising PspF–A–C–B–ArcB controls psp expression. One key regulatory point is the negative control of PspF imposed by its binding to PspA. It has been proposed that under stress conditions, the IM-bound sensors PspB and PspC receive and transduce the signal(s) to PspA via protein–protein interactions, resulting in the release of the PspA–PspF inhibitory complex and the consequent induction of psp. In this work we demonstrate that PspB self-associates and interacts with PspC via putative IM regions. We present evidence suggesting that PspC has two topologies and that conserved residue G48 and the putative leucine zipper motif are determinants required for PspA interaction and signal transduction upon stress. We also establish that PspC directly interacts with the effector PspG, and show that PspG self-associates. These results are discussed in the context of formation and function of the Psp regulatory complex.

Phage Shock Protein C (PspC) of Yersinia enterocolitica Is a Polytopic Membrane Protein with Implications for Regulation of the Psp Stress Response

“…Regardless of whether or not restraint was applied, the consensus predictions were identical. TOPCONS analysis of E. coli PspC also predicts the polytopic membrane arrangement, with both termini inside (34). Therefore, TOPCONS prediction agrees with the arrangement of PspC revealed by our experimental analysis.…”

“…The integral cytoplasmic membrane proteins PspB and -C play a critical role in inducing the Psp system. They are excellent candidates to sense the inducing signal and transduce it to the cytoplasm, perhaps by interacting with PspA and sequestering it from PspF (34,58). Consistent with this, Y. enterocolitica PspC mutants that are unable to induce pspA operon expression in response to secretin induced-stress have been isolated (25).…”

“…However, the situation is less clear for PspC. Jovanovic et al noticed that different topology prediction programs did not agree on the topology of E. coli PspC (34). Some predicted the C terminus to be outside, others inside, and some predicted two transmembrane domains with both termini in the cytoplasm.…”

“…The topology of PspC has been addressed experimentally in just one study, where the alkaline phosphatase activity of a PspC-PhoA fusion protein supported the bitopic arrangement with the C terminus in the periplasm (39). However, it has been suggested that the C terminus of PspC might interact with PspA to activate the Psp system (34). To reconcile this suggestion with the apparent location of the PspC C terminus in the periplasm, Jovanovic et al proposed that PspC might change its membrane topology in response to an inducing signal (34).…”

“…However, it has been suggested that the C terminus of PspC might interact with PspA to activate the Psp system (34). To reconcile this suggestion with the apparent location of the PspC C terminus in the periplasm, Jovanovic et al proposed that PspC might change its membrane topology in response to an inducing signal (34). All of this uncertainty surrounding the membrane topology of PspC prompted us to investigate it in our model organism Y. enterocolitica using a variety of independent approaches.…”