Characterization of a new Cu/Zn-superoxide dismutase from Beauveria bassiana and two site-directed mutations crucial to its antioxidation activity without chaperon

A Cu/Zn-superoxide dismutase (SOD) was characterized for the first time from Beauveria bassiana by gene cloning, heterogeneous expression and function analysis. This 154-aa SOD (BbSod1) was deduced from a 465-bp gene cloned, showing 49–96% sequence identity to Cu/Zn-SODs from other 57 fungi. BbSod1 and its form engineered with two site-directed mutations P143S and P145L (BbSod1-Mut) or a fused copper chaperon Lys7 (BbSod1-Lys7) were expressed well in Escherichia coli. Crude extracts and purified BbSod1-Mut from cell cultures exhibited much higher antioxidation activities than the counterparts of BbSod1-Lys7 whereas BbSod1 showed no substantial activity. The engineered enzymes were best induced by overnight incubation at 20 °C in Luria-Bertani medium including 2.5 mM Cu²⁺, 0.5 mM Zn²⁺ and 0.5 mM isopropyl-d-thiogalactopyranoside after 5-h growth to log-phase at 37 °C. Our results highlight alternative means to producing highly active fungal Cu/Zn-SOD in E. coli by making use of the two site-directed mutations without chaperon.