Purification of wild-type LipBL and variants after co-expression with chaperones.
Wild-type LipBL and its variants were coexpressed with the GroEL/GroES chaperone system and cells were disrupted to separate soluble proteins from inclusion bodies, as described above. LipBL and variants carrying a His6-tag were purified from soluble fractions by immobilized metal-affinity chromatography (IMAC) using a gravity-flow Ni-NTA agarose column (Qiagen). Before loading onto the column, the soluble fraction was incubated with 2 mM ATP for 10 min at 37 uC to dissociate recombinant enzyme from chaperone. After removal of non-specifically bound proteins by washing with 100 mM Tris/HCl buffer, pH 8, supplemented with 300 mM NaCl and 40 mM imidazole, LipBL and variants were eluted with the same buffer containing 250 mM imidazole. Elution fractions containing His6-tagged LipBL and variants were diluted 50-fold and concentrated using centrifugal filter units with 10 kDa size-exclusion membranes (Centricon,Millipore) to reduce the concentration of imidazole, which interferes with activity assays. Protein concentrations were determined after purification using Advanced Image Data Analysis (AIDA) 2D software (version 4.18.028) with a calibration curve based on BSA