The putative thiol-disulphide interchange protein DsbG from Acidithiobacillus ferrooxidans has disulphide isomerase activity

The putative thiol-disulphide interchange protein, DsbG, is involved in the formation and rearrangement of disulphide bonds in Acidithiobacillus ferrooxidans but its exact role is so far unclear. The gene encoding DsbG from A. ferrooxidans ATCC 23270 was cloned and expressed in Escherichia coli BL21 (DE3). The protein was purified by one- step affinity chromatography. The scRNaseA could be rescued to 89% of the native RNaseA activity by using the purified DsbG of A. ferrooxidans. This characteristic is unique and different from that of DsbG from E. coli, which does not catalyse the oxidative refolding of RNaseA in vitro. Site-directed mutagenesis of the DsbG protein revealed that Cys119A and Cys122A do not possess the disulphide isomerization activity, indicating Cys119 and Cys122 are catalytic residues and play a crucial role in disulphide isomerization.