Expression and function of two chaperone proteins, AtGroEL and AtGroES, from Acidithiobacillus ferrooxidans ATCC 23270

Two molecular chaperone genes encoding the Acidithiobacillus ferrooxidans Hsp60 (AtGroEL) and Hsp10 (AtGroES), respectively were introduced into Escherichia coli using the pLM1 expression vector. Then the AtGroEL and AtGroES proteins were overexpressed successfully in Escherichia coli BL21 (DE3), and purified by one-step immobilized metal affinity chromatography. The ATPase assay showed that the proteins were in active form, and the ATPase activity of AtGroEL was temperature dependent with an optimal temperature of 50A degrees C, but the co-chaperonin AtGroES inhibited the ATPase activity of AtGroEL. The chaperonin function of the recombinant proteins was examined using three different protein substrates in vitro, and the results showed that AtGroEL/AtGroES chaperone system could facilitate the refolding of the thermodenatured rusticyanin and recover the activity of thermodenatured ArsH protein. In addition, it could improve the thermal stability of xylanase. Molecular modelling for AtGroEL protein revealed that residues of Tyr199, Ser201, Tyr203, Phe204, Leu234, Leu237, Leu259, Val263 and Val264 were necessary for binding the denatured polypeptides.