The supernatant was mixed with 300 µl of Ni -
NTA agarose (Qiagen), and the proteins were allowed to bind for 3 hours, followed by washing with 20 ml of resuspension buffer, and eluted with 500 µl of elution buffer (20 mM NaHPO4, 300 mM NaCl, 10 % glycerol, 150 mM Imidazole, pH 7.8).