pGEX-4T-1-B2M was constructed using the GST gene fusion system according to the manufacturer’s instructions. To produce glutathione S-transferase (GST) and GST-B2M fusion proteins, pGEX-4T-1 and pGEX-4T-1-B2M were individually transfected into BL21 cells. Protein expression was induced by ispropylb-D-1-thiogalactopyranoside (IPTG). GST-B2M and GST proteins were purified by binding to Glutathione Sepharose-4B beads. Then, beads were incubated with mouse brain lysates from C57BL/6J mice at 4 °C for 12 h on a rotator, and then were washed with the washing buffer three times. Beads-bound complexes were eluted by boiling, and subjected to SDS-PAGE and silver staining. The proteins were identified by Mass Spectrometry.