Overexpression of glutaredoxin-2 from Cyanobacterium Synechocystis PCC 6803 in Escherichia coli conferring enhanced salt stress tolerance

Glutaredoxin (Grx), widely found in bacteria, plants, and mammalian cells, is an electron carrier for ribonucleotide reductase and a general glutathione-disulfide reductase of importance for redox regulation. Cyanobacterium Synechocystis strain PCC 6803 contains two genes (slr1562 and ssr2061) encoding two glutaredoxins (Grx1 and Grx2, respectively). The amino acid sequences deduced from both proteins share high identity with those of Grxs from other organisms. In the present study, we found that the steady-state transcript levels of ssr2061 were increased in the wildtype of Cyanobacterium cells under oxidative stress conditions imposed by high salinity (NaCl), chilling or application of H2O2, methylviologen or t-butyl hydroperoxide. Moreover, the protein Grx2 encoded by ssr2061 was successfully overexpressed as a soluble fraction in Escherichia coli JM109. The transformed Escherichia coli cells showed high tolerance to NaCl (over than 700 mM) mediating growth inhibition compared to cells transformed with the vector alone.