Expression and Purification of SARS CoV-2 RBD Protein in the Prokaryotic Expression System to Evaluate the IgG Antibody in the Serums of COVID-19 Recovered Cases

Background and Objectives One of the most important proteins of the SARS-COV-2 virus is S protein, which consists of S1 and S2 subunits. The most important region insubunit S1 is the receptor binding region (RBD), which plays a key role in binding toACE receptors. The RBD is a conserved region in S protein that is the target of theimmune system and the production of antibodies against the virus. Due to theimportance of this region in the production of neutralizing antibodies, it can be a goodcandidate for vaccine development and production of diagnostic kits. Therefore, thepresent study aimed to assess the response rate of antibodies in the serum ofrecovered COVID-19 cases using recombinant RBD protein produced in the prokaryoticexpression system as an inexpensive expression system.Subjects and Methods In this study, the recombinant PET22b-RBD construct wastransformed to the Escherichia coli (BL21) host, and the bacterial cells were culturedin a culture medium; thereafter, protein expression was induced using isopropyl beta-D-thiogalactoside (IPTG). The expression of recombinant RBD protein was confirmedby acrylamide gel (SDS-PAGE) and Western blotting. Finally, the desired protein wasextracted using a Ni-NTA column and applied in an indirect ELISA.Results In comparison with the serum of healthy individuals (cut off: 0.412), nosignificant increase was observed in the response of 30 serum samples to therecombinant RBD protein.Conclusion The recombinant RBD protein produced in the prokaryotic host did notrespond significantly to the antibodies in the serum of recovered COVID-19 patientsand cannot be used for diagnostic purposes.