Expression of a novel thermostable Cu,Zn-superoxide dismutase from Chaetomium thermophilum in Pichia pastoris and its antioxidant properties

A new superoxide dismutase (SOD) gene from the thermophilic fungus Chaetomium thermophilum (Ctsod) was cloned and expressed in Pichia pastoris and its gene product was characterized. The specific activity of the purified CtSOD was 2,170 U/mg protein. The enzyme was inactivated by KCN and H₂O₂ but not by NaN₃, confirming that it belonged to the type of Cu, ZnSOD. The amino acid residues involved in coordinating copper and zinc were conserved. The recombinant CtSOD exhibited optimum activity at pH 6.5 and 60°C. The enzyme retained 65% of the maximum activity at 70°C for 60 min and the half-life was 22 and 7 min at 80 and 90°C, respectively. The recombinant yeast exhibited higher stress resistance than the control yeast cells to salt and superoxide-generating agents, such as paraquat and menadione.