Abstract
The EvgS/EvgA two-component signal transduction system in Escherichia coli is activated under mildly acidic pH conditions. Upon activation, this system induces the expression of a number of genes that confer acid resistance. The EvgS histidine kinase sensor has a large periplasmic domain that is required for perceiving acidic signals. In addition, we have previously proposed that the cytoplasmic linker region of EvgS is also involved in the activation of this sensor. The cytoplasmic linker region resembles a Per-ARNT-Sim (PAS) domain, which is known to act as a molecular sensor that is responsive to chemical and physical stimuli and regulates the activity of diverse effector domains. Our EvgS/EvgA reporter assays revealed that under EvgS-activating mildly acidic pH conditions, EvgS was activated only during aerobic growth conditions, and not during anaerobic growth. Studies using EvgS mutants revealed that C671A and C683A mutations in the cytoplasmic PAS domain activated EvgS even under anaerobic conditions. Furthermore, among the electron carriers of the electron transport chain, ubiquinone was required for EvgS activation. The present study proposes a model of EvgS activation by oxidation and suggests that the cytoplasmic PAS domain serves as an intermediate redox switch for this sensor.
Highlights
Bacteria utilize two-component signal transduction systems (TCSs) to respond and adapt to fluctuating environmental conditions (Stock et al, 2000)
Since the EvgS sensor has a cytoplasmic PAS domain adjacent to the membrane, we examined whether respiratory growth conditions affect EvgS activity in vivo
We examined EvgS expression in cells used in the reporter assays and found that EvgS levels were fairly constant among the different incubation conditions (Figure 1B, full gel results shown in Supplementary Figure 1)
Summary
Bacteria utilize two-component signal transduction systems (TCSs) to respond and adapt to fluctuating environmental conditions (Stock et al, 2000). Input of a specific stimulus to the HK sensor causes autophosphorylation of a conserved histidine residue in the catalytic core This phosphate group is subsequently transferred to the partner RR; the phosphorylated RR functions mainly by regulating gene expression, which is served as the output. In a prototypical HK sensor, the extracellular sensor region perceives environmental stimuli and transduces the information via the transmembrane segment to the cytoplasmic region, where the catalytic core resides. Additional protein domains such as HAMP (HK, adenylyl cyclases, methyl-accepting proteins, and other prokaryotic signaling proteins) and PAS (Per-ARNT-Sim) are often found between the transmembrane segment and the catalytic core. A typical HK perceives the stimuli at its extracellular sensor domain, some HK sensors lack the extracellular region
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