Molecular cloning, expression, and functional characterization of 70-kDa heat shock protein, DnaK, from Bacillus halodurans

In the present study, we report cloning, sequencing, and functional characterization dnaK gene of B. halodurans that is the central component in cellular network of molecular chaperones. The 3D structures of DnaK obtained by I-TASSER server showed that the overall structures of DnaK from B. halodurans and human HSP70 chaperone BiP are very similar with a homology of 88.8%. The purified recombinant DnaK consists of a His-tag at C-terminus and show a band on approximately 70-kDa region in SDS-PAGE. The resultant refolding assay revealed that the refolding rate was considerably improved by the addition of the novel DnaK chaperone for the refolding of heat-denatured carbonic anhydrase. Also, salt resistance experiments indicated that E. coli + DnaK survival had enhanced by 4.4-fold as compared with control cells in 0.4 M NaCl. The number of E. coli + DnaK colonies was 2.5-fold higher than control colonies in pH 9.5. We showed that DnaK refolding functions were decreased by increasing Cd²⁺ in nanomolar concentrations. Hg²⁺ had a biphasic effect on recombinant DnaK refolding function: inhibition at low and stimulation at high concentrations. It was concluded that the DnaK from B. halodurans can potentially be employed for improving functional properties of proteins in various applications.