The phage shock protein (Psp) system is a widely conserved cell envelope stress response that is essential for the virulence of some bacteria, including Yersinia enterocolitica. Recruitment of PspA by the inner membrane PspB-PspC complex characterizes the activated state of this response. The PspB-PspC complex has been proposed to be a stress-responsive switch, changing from an OFF to an ON state in response to an inducing stimulus. NT in vivo. These findings have provided the first insight into the regulatory function of the N-terminal cytoplasmic domain of PspC, revealing that its ability to participate in an inhibitory complex is essential to silencing the Psp response.
IMPORTANCEThe phage shock protein (Psp) response has generated widespread interest because it is linked to important phenotypes, including antibiotic resistance, biofilm formation, and virulence in a diverse group of bacteria. Therefore, achieving a comprehensive understanding of how this response is controlled at the molecular level has obvious significance. An integral inner membrane protein complex is believed to be a critical regulatory component that acts as a stress-responsive switch, but some essential characteristics of the switch states are poorly understood. This study provides an important advance by uncovering a new protein interaction domain within this membrane protein complex that is essential to silencing the Psp response in the absence of an inducing stimulus. E xtracytoplasmic stress responses (ESRs) are a widely used strategy to protect bacterial cell envelopes from conditions and external agents that could compromise them. They monitor features within the cell envelope and direct a transcriptional response to potentially deleterious changes (1-4). One widely conserved ESR is the phage shock protein (Psp) response, which protects the cytoplasmic membrane from events that could increase its permeability (recently reviewed in references 5 and 6). Although it was discovered and initially studied in Escherichia coli (7), the Psp response is conserved in many Gram-negative bacteria, including the human pathogens Yersinia enterocolitica and Salmonella enterica serovar Typhimurium, where it is essential for virulence (8-11). Sequence and/or functional homologues of some Psp components also occur in Gram-positive bacteria, mycobacteria, archaea, and plant chloroplasts (e.g., references 1, 12, and 13). Furthermore, in addition to virulence, the Psp response has been linked to other important processes in bacteria, including the formation of biofilms and antibiotic-tolerant persister cells (14,15).Most research to date has focused on the Psp responses of E. coli and Y. enterocolitica, in which the core components are encoded by pspF and the adjacent divergently transcribed pspABC genes. There are a small number of additional genes in the Psp regulons of these two species, but pspF, pspA, pspB, and pspC are considered to encode the core components because only they are essential for regulation and/or stress tolerance (5,6,16,17...