Several colonies of E. coli were incubated in 10 ml 1x LB medium supplemented with 100 µg/ml ampicillin. The pre-culture was incubated at 37°C for 4 hours. After incubation, the pre-culture was added to 1 liter of 1x LB medium supplemented with 100 µl/ml ampicillin. The culture was incubated to OD600 = 0,8 and expression was induced by the addition of IPTG to a final concentration of 0.5 mM. The cell culture was incubated at 20°C, 150 rpm, 16 h and harvested by centrifugation at 4000 rpm, 4°C, 25 min. The cell pellet was resuspended in approximately 30 ml of harvesting purification buffer A: 16.4 mM K2HPO4, 3.6 mM KH2PO4, 400 mM NaCl, 10 mM imidazole, pH 7.5, and frozen at -70°C.