Emulsiflex c5 cell homogenizer

Proteins bearing an N-terminal, TEV-cleavable His₆-tag were produced in E. coli Rosetta 2 (DE3) or E. coli BL21 (DE3) RIL cells in auto-inducing ZY medium [58 (link)] for 24 h at 18 °C. The following steps were performed at 4 °C. Cells were resuspended in solubilization buffer (50 mM sodium phosphate, pH 8.0, 500 mM NaCl, 30 mM imidazole, 5 mM β-mercaptoethanol) and lyzed using an EmulsiFlex-C5 cell homogenizer (Avestin). The soluble fraction was separated from the insoluble fraction by centrifugation for 30 min at 55,900 x g in an Avanti J-26 XP centrifuge (Beckman Coulter). Target proteins were captured on Ni²⁺-NTA resin (GE Healthcare), washed with solubilization buffer and eluted with elution buffer (250 mM imidazole, pH 8.0, 300 mM NaCl, 5 mM β-mercaptoethanol). Tags were cleaved with 1:50 TEV during overnight dialysis against 10 mM sodium phosphate, pH 8.0, 300 mM NaCl, 30 mM imidazole, 5 mM β-mercaptoethanol, and cleaved samples were again passed over Ni²⁺-NTA resin. The flow-through was collected, concentrated, and subjected to size exclusion chromatography (SEC) in SEC buffer (10 mM Tris-HCl, pH 8.0, 300 mM NaCl, 0.1 mM EDTA, 1 mM DTT) using Superdex 75 and Superdex 200 columns (GE Healthcare). Peak fractions were analyzed by SDS-PAGE. Fractions containing the target protein were pooled, concentrated, and shock-frozen in liquid nitrogen.