For protein expression, E. coli (BL21) cells (Thermo Fisher Scientific, USA) were transformed with the plasmids and selected on an agar plate containing 100 µg ampicillin/mL. A single colony was used to inoculate 5 mL of LB medium (100 µg ampicillin/mL). The cells were grown over night at 37 °C with constant shaking (225 rpm). The suspension was transferred into 400 mL of LB medium (100 µg ampicillin /mL) and grown another 4 h (37 °C, 225 rpm).