Expression and purification of truncated recombinant human angiotensin converting enzyme 2 (trhACE2) capable of binding spike protein of SARS-CoV-2

SARS-CoV-2 infects the host through the interaction be-tween spike protein and the ACE2 (Angiotensin convert-ing enzyme 2) receptor on the host cell surface. There-fore, ACE2 is considered as a key target in drug devel-opment against COVID-19. In this study, we generated the truncated recombinant human ACE2 (trhACE2) expressed on Escherichia coli and evaluated its binding activity to spike protein of SARS-CoV-2. The sequence of ACE2 (18-119 aa) was cloned into pET28a(+) plasmid and transformed into E. coli DH5α strain and finally was transferred to E. coli BL21 (DE3) cells for protein expression. Protein trhACE2 was purified by affinity chromatography using a HisTrap HP column. Protein purity was above 95% and production yield was 75 mg/l. The purified protein was refolded by dialysis method. trhACE2 was evaluated for its ability to bind the spike protein by sandwich ELISA assay and surface plasmon resonance (SPR). The results showed that trhACE2 has the ability to bind spike protein of SARS-CoV-2 with the equilibrium dissociation constant Kd=15.7 nM. With a relatively simple and inexpensive expression and purifi-cation process on E. coli system, there is the potential to develop trhACE2 for preventive and supportive thera-pies against COVID-19.