Characterization of Thiol Peroxidase‐Glutaredoxin Fusion from Anabaena sp. (PCC7120) Acting as a Hydrogen Peroxide Peroxidase

Abstract

Recently, novel hybrid thiol peroxidase (TPx or Prx: Peroxiredoxin) fused with a glutaredoxin (Grx) (TPx-Grx fusion) was found from some pathogenic bacteria. The hybrid protein reduces peroxides with the use of GSH as the proton donor to the Grx domain. A sequence coding for a hybrid thiol peroxidase was isolated from Anabaena sp. (PCC7120) genome and subsequently inserted into an expression plasmid. The recombinant protein was produced in Escherichia coli cells and purified to homogeneity. It was shown that the protein is dimeric and possesses two conserved cysteines (Cys) in the TPx domain and two Cys (CxxC) in the Grx domain. The hybrid protein can reduce various hydroperoxides, but with a much better efficiency for hydrogen peroxide than t-butyl hydroperoxide, cumene hydroperoxide, and linoleic acid hydroperoxide (hydrogen peroxide > t-butyl hydroperoxide >> cumene hydroperoxide > linoleic acid hydroperoxide) in the presence of GSH as the unique exogenous proton donor. The protein expression level of the hybrid protein in the cyanobacteria upon oxidative stress was assayed using an immunoblot. The protein is very highly expressed in response to oxidative and heat-shock stresses. Based on this finding, we propose that Anabaena TPx-Grx fusion, which represents a GSH-supported hydrogen peroxide peroxidase, plays a vital role in the defense of cyanobacteria against oxidative damage.