Cells expressing the His-tagged protein can be lysed by sonication on ice in binding buffer (20 mM NaH2PO4, 300 mM NaCl, 10mM imidazole pH 7.4). Approximately 3–5 ml of loading buffer should be used per gram (wet weight) of cells. Keep the lysate as cold as possible to minimize possible proteolysis. In addition, an EDTA-free protease inhibitor may be added (e.g., cOmplete™, EDTA-free Protease Inhibitor Cocktail, Sigma Aldrich). Immediately centrifuge lysate by spinning at 20,000 g for 30 min at 4°C.