Beschreibung:
<jats:title>ABSTRACT</jats:title>
<jats:p>
The phage shock protein (Psp) system is a widely conserved cell envelope stress response that is essential for the virulence of some bacteria, including
<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Yersinia enterocolitica</jats:named-content>
. 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. In the OFF state, PspA cannot access its binding site in the C-terminal cytoplasmic domain of PspC (PspC
<jats:sup>CT</jats:sup>
), because this site is bound to PspB. PspC has another cytoplasmic domain at its N-terminal end (PspC
<jats:sup>NT</jats:sup>
), which has been thought to play a role in maintaining the OFF state, because its removal causes constitutive activation. However, until now, this role has proved recalcitrant to experimental investigation. Here, we developed a combination of approaches to investigate the role of PspC
<jats:sup>NT</jats:sup>
in
<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Y. enterocolitica</jats:named-content>
. Pulldown assays provided evidence that PspC
<jats:sup>NT</jats:sup>
mediates the interaction of PspC with the C-terminal cytoplasmic domain of PspB (PspB
<jats:sup>CT</jats:sup>
)
<jats:italic>in vitro</jats:italic>
. Furthermore, site-specific oxidative cross-linking suggested that a PspC
<jats:sup>NT</jats:sup>
-PspB
<jats:sup>CT</jats:sup>
interaction occurs only under noninducing conditions
<jats:italic>in vivo</jats:italic>
. Additional experiments indicated that mutations in
<jats:italic>pspC</jats:italic>
might cause constitutive activation by compromising this PspC
<jats:sup>NT</jats:sup>
binding site or by causing a conformational disturbance that repositions PspC
<jats:sup>NT</jats:sup>
<jats:italic>in vivo</jats:italic>
. 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.
</jats:p>
<jats:p>
<jats:bold>IMPORTANCE</jats:bold>
The 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.
</jats:p>