PsaF Is a Membrane-Localized pH Sensor That Regulates psaA Expression in Yersinia pestis

Abstract

The Yersinia pestis pH 6 antigen (PsaA) forms fimbria-like structures and is required for full virulence during bubonic plague. High temperature and low pH regulate PsaA production and while recent work has uncovered the molecular aspects of temperature control, the mechanisms underlying the unusual regulation by pH are poorly understood. Using defined growth conditions, we recently showed that high levels of PsaE and PsaF (two regulatory proteins required for expression of psaA ) are present at mildly acidic pH, but these levels are greatly reduced at neutral pH, resulting in low psaA expression. In prior work, the use of translational reporters suggested that pH had no impact on translation of psaE and psaF , but rather affected protein stability of PsaE and/or PsaF. Here, we investigated the pH-dependent post-translational mechanisms predicted to regulate PsaE and PsaF stability. Using antibodies that recognize the endogenous proteins, we showed that the amount of PsaE and PsaF is defined by a distinct pH threshold. Analysis of histidine residues in the periplasmic domain of PsaF suggested it functions as a pH-sensor and indicated that the presence of PsaF is important for PsaE stability. At neutral pH, when PsaF is absent, PsaE appears to be targeted for proteolytic degradation by regulated intramembrane proteolysis. Together, our work shows that Y. pestis utilizes PsaF as a pH sensor to control psaA expression by enhancing the stability of PsaE, an essential psaA regulatory protein. IMPORTANCE Yersinia pestis is a bacterial pathogen that causes bubonic plague in humans. As Y. pestis cycles between fleas and mammals, it senses the environment within each host to appropriately control gene expression. PsaA is a protein that forms fimbria-like structures and is required for virulence. High temperature and low pH together stimulate psaA transcription by increasing the levels of two essential integral membrane regulators, PsaE and PsaF. Histidine residues in the PsaF periplasmic domain enable it to function as a pH-sensor. In the absence of PsaF, PsaE (a DNA binding protein) appears to be targeted for proteolytic degradation, thus preventing expression of psaA . This work offers insight into mechanisms that bacteria use to sense pH and control virulence gene expression.

Co-component signal transduction systems: Fast-evolving virulence regulation cassettes discovered in enteric bacteria

“…Thus, ToxS is thought to activate ToxR by protecting it from degradation ( 53 ). Similar chaperone-like mechanisms are proposed for the TcpP/TcpH and PsaE/PsaF co-components ( 54 , 55 ). While degradation may represent one mode of regulation for these co-component systems, their evolutionary relationship to the VtrA/VtrC bile acid sensor suggests that they may form heterodimers and respond to lipid-like environmental cues.…”

Co-Component Signal Transduction Systems: fast-evolving virulence regulation cassettes discovered in enteric bacteria

“…Thus, ToxS is thought to activate ToxR by protecting it from degradation (53). Similar chaperone-like mechanisms are proposed for the TcpP/TcpH and PsaE/PsaF co-components (54,55). While degradation might represent one mode of regulation for these co-component systems, their evolutionary relationship to the VtrA/VtrC bile acid sensor suggests they might form heterodimers and respond to a lipid-like environmental cues.…”

Regulation of yeast Snf1 (AMPK) by a polyhistidine containing pH sensing module

“…sapiens at a single histidine H212 ( Vercoulen et al., 2017 ) or utilizing multiple histidine residues in PsaF of Y . pestis ( Quinn et al., 2021 ) or the human prion PrP ( Zahn, 2003 ).…”