Expression and Purification of Functional SARS-CoV-2 RBD in E. coli for Therapeutic and Diagnostic Purposes

Abstract SARS-CoV-2 causes a severe respiratory disease known as COVID-19 and is responsible for a global viral pandemic. The SARS-CoV-2 receptor binding domain (RBD) is located on the spike protein (S), which is dedicated for identifying and binding to the angiotensin converting enzyme 2 (ACE2) receptor. The RBD is an important target for development of virus neutralizing antibodies, vaccines, and inhibitors. In this study, recombinant SARS-CoV-2 RBD was expressed in E. coli BL21 (DE3) and purified as well as its binding activity was determined. Purification was conducted by Ni-NTA column. ELISA and flow cytometry assays were conducted to evaluate the binding ability of recombinant RBD to different anti-RBD antibodies and native ACE2 receptor on HEK293A cells, respectively. ELISA results showed that antibodies produced in the human sera could bind to the recombinant RBD protein as well as the commercial anti-RBD antibody. Also, flow cytometry analysis showed that the recombinant RBD was able to bind to human ACE2 on the surface of HEK293A cells. Our outcomes displayed that the recombinant RBD expressed in E. coli strain has biological activity and can be used as an antigen for development of diagnosis kits and vaccines as well as a tool for screening drugs against SASR-CoV-2.