Recombinant Expression and Purification of Nurr1 LBD Protein. The Nurr1 LBD (aa 362-598) was subcloned into pNIC28-Bsa4. The recombinant protein containing an N-terminal His6-tag was expressed in Escherichia coli BL21(DE3)-R3-pRARE2, cultured in TB. Expression was induced with 0.5 mM IPTG at 18 °C overnight. The protein was purified by Ni 2+-affinity chromatography followed by TEV treatment to remove the histidine tag. The cleaved protein was further purified by reverse Ni 2+ -affinity chromatography and size exclusion chromatography.