Multiple histidines in the periplasmic domain of the Salmonella enterica sensor kinase SsrA enhance signaling in response to extracellular acidification

The two-component regulatory system SsrA-SsrB in Salmonella enterica controls expression of a virulence gene program required for intracellular survival in host cells. SsrA signaling is induced within the acidic host vacuole in which the bacteria reside; however, the mechanism by which SsrA senses this intracellular environment is unknown. Here, we show that the periplasmic sensor domain of SsrA is enriched in histidine residues that increase …