2.3 Protein purification
The expression plasmids for His-tagged intracellular domain of LRP6/1394-1613 (His-LRP6-ICD), GST-tagged Axin1 1-300 (GST-Axin1-300), GST-tagged Axin1 301-521 (GST-Axin301-521), and GST-tagged Axin1 522-862 (GST-Axin522-862) were constructed and expressed in Escherichia coli (E. coli ) BL21. The expression of fusion proteins was induced with IPTG (Sigma-Aldrich, Shanghai, China) at 16 or 28 °C for 8-12 h. His-LRP6-ICD was purified by NiNTA Purification System, while GST and GST fusion proteins were purified by affinity chromatography with glutathione-sepharose 4B beads (GE Healthcare, Piscataway, NJ, USA). The factor Xa protease was used to remove GST and His tag from fusion proteins.