As a second purification step, a size exclusion chromatography was performed on an Enrich™ SEC650 column on a Bio-Rad NGC™ chromatography system (Hercules, USA) using the gel filtration buffer (10 mM Tris/HCl, pH 8.0). Fractions containing the protein were combined and concentrated using the Amicon ® Pro Purification System with a 10 kDa cut-off.