The zinc ion-chelating agent TPEN reduces the CpxP-mediated negative regulation of the CpxAR two-component system in Escherichia coli

CpxAR is a two-component signal transduction system found in Gram-negative bacteria that senses environmental and cellular stresses and regulates gene expression. The inner membrane bound protein CpxA senses cell envelope stress and transmits a signal to cytosolic CpxR via a phosphorylation cascade. CpxA is negatively regulated by the periplasmic protein, CpxP. The structure of CpxP has been solved and shown to adopt a dimeric alpha helical fold bound to zinc ions. We hypothesised that zinc plays a role in CpxP-mediated regulation of CpxAR activity. Using plasmid-encoded lux reporter genes, we show that in the presence of TPEN, a zinc (II) chelator, expression of genes regulated by the CpxAR system increases in wild type Escherichia coli DH5α, but not in CpxP-deficient mutants. CpxA and CpxR deficient mutants do not respond to changes in pH or the addition of TPEN. Our data suggest that zinc is required for CpxP-mediated inhibition of CpxAR activity.