A practical method of expression, purification and identification of beta-site app-cleaving enzyme

Abstract

Objective To introduce a practical method that can be used to efficiently express, purify and identify Alzheimer' s disease (AD) related beta-site app-cleaving enzyme 1 (BACE1) in common eukaryotic cells. Methods BACE1 cDNA was fished out from human brain cDNA library and ligated into the pEGFP-c3 expression vector, and then, the recombinant plasmid was transfected into the HEK293 cells. The BACE1 protein was purified with TALON Mental Affinity Resins column. The target protein was identified by Western blotting and fluorescence resonance energy transfer (FRET). BACE1 Activity Assay Kit was employed to test the activity of purified BACE1 in vitro. The recombinant BACE1/pEGFP-c3 plasmid and amyloid precusor protein (APP)/pDsRed-Monomer-N1 plasmid were co-transfected to the HEK293 cells and the cleavage activity of BACE1 in the cells was identified by Western blotting. Results The sequencing data of the obtained BACE1 gene were identical with those in GenBank. Activity test showed that the fluorescent values of blank controls, expressed BACE1 and standard BACE1 were 55.013±3.597, 1836.629±154.195 (n=3) and 2639.548± 207.1901 (n=3), respectively; as compared with the control group, significant differences were noted in both of the two groups (F=78.681, P=0.000); however, there is no significant difference between expressed BACE1 and standard BACE1 groups (P>0.05). Western blotting showed the co-transfected BACE1 could cleave APP in HEK293 cells and the CTF-APP band was detectable. Conclusion A practical protocol is established for high expression, purification and identification of BACE1 in HEK293 cells, which is helpful to obtain BACE1, an important molecular target in AD research and treatment. Key words: Alzheimer' s disease; Beta-site app-cleaving enzyme 1; Eukaryotic cell