Biophysical and physiological characterization of ZraP from Escherichia coli, the periplasmic accessory protein of the atypical ZraSR two-component system

Biochem J. 2015 Dec 1;472(2):205-16. doi: 10.1042/BJ20150827. Epub 2015 Oct 5.


The ZraSR system belongs to the family of TCSs (two-component signal transduction systems). In Escherichia coli, it was proposed to participate in zinc balance and to protect cytoplasmic zinc overload by sequestering this metal ion into the periplasm. This system controls the expression of the accessory protein ZraP that would be a periplasmic zinc scavenger. ZraPSR is functionally homologous with CpxPAR that integrates signals of envelope perturbation, including misfolded periplasmic proteins. The auxiliary periplasmic regulator CpxP inhibits the Cpx pathway by interacting with CpxA. Upon envelope stress sensing, the inhibitory function of CpxP is relieved, resulting in CpxR activation. Similarly to CpxPAR, ZraPSR probably plays a role in envelope stress response as a zinc-dependent chaperone activity was demonstrated for ZraP in Salmonella. We have purified ZraP from E. coli and shown that it is an octamer containing four interfacial metal-binding sites contributing to dimer stability. These sites are located close to the N-terminus, whereas the C-terminus is involved in polymerization of the protein to form a tetramer of dimers. In vitro, ZraP binds copper with a higher affinity than zinc and displays chaperone properties partially dependent on zinc binding. In vivo, zinc-bound ZraP is a repressor of the expression of the zraPSR operon. However, we have demonstrated that none of the Zra proteins are involved in zinc or copper resistance. We propose an integrated mechanism in which zinc is a marker of envelope stress perturbation and ZraPSR TCS is a sentinel sensing and responding to zinc entry into the periplasm.

Keywords: Escherichia coli; ZraPSR; chaperone; two-component system (TCS); zinc resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Absorption, Physiological*
  • Amino Acid Sequence
  • Binding Sites
  • Biophysical Phenomena
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / isolation & purification
  • Carrier Proteins / metabolism
  • Copper / metabolism
  • Escherichia coli K12 / physiology*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / isolation & purification
  • Escherichia coli Proteins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Kinetics
  • Molecular Chaperones / chemistry
  • Molecular Chaperones / genetics
  • Molecular Chaperones / isolation & purification
  • Molecular Chaperones / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Operon
  • Periplasmic Proteins / chemistry
  • Periplasmic Proteins / genetics
  • Periplasmic Proteins / isolation & purification
  • Periplasmic Proteins / metabolism*
  • Protein Stability
  • Protein Structure, Quaternary
  • Recombinant Proteins
  • Signal Transduction*
  • Trans-Activators / genetics
  • Trans-Activators / metabolism
  • Zinc / metabolism*


  • Carrier Proteins
  • Escherichia coli Proteins
  • Molecular Chaperones
  • Periplasmic Proteins
  • Recombinant Proteins
  • Trans-Activators
  • zraP protein, E coli
  • zraR protein, E coli
  • zraS protein, E coli
  • Copper
  • Zinc