Antibodies Produced Toward Recombinant RBD and Nucleocapsid Neutralize SARS-COV-2

The highly contagious SARS-COV-2 virus spread rapidly from China and formed a global pandemic. The virus has infected over 509 million people worldwide and killed about 6.32 million up to date. Up on invasion, the Receptor Binding Domain (RBD) of Spike protein plays a crucial role in the entry of the virus into the host cell. The virus N protein is another protein that has a critical role for genome packaging.

As bioinformatics approaches, the cassette design, codon adaptation, and protein stability were investigated in this study. Synthetic genes of RBD and N were cloned separately in pET28a + expression vector. They were transferred into Escherichia coli (E. coli) BL21 DE3 host cell, and expression of recombinant proteins was induced with IPTG. The recombinant proteins were purified by column chromatography and approved by Western blotting. Animal immunization was performed with each of the recombinant proteins individually and in combination of the two. The antibody titer of the blood serum from control and immunized mice groups was determined by ELISA technique. Finally, the anti-spike neutralization test was performed.

The expression and purification of RBD protein were monitored on SDS-PAGE, two bands of about 28 and 45 kDa for RBD and N appeared on gel distinctly, which were further validated by Western blotting. According to ELISA results, related antibodies were traced to a dilution of 1/64000 in immunized sera. The neutralization test exhibited produced antibodies' potency to bind the virus proteins. Using SPSS software, statistical analysis was performed by Duncan's test and T-test.

According to the present study, recombinant proteins, either RBD alone or in combination with N adequately stimulated the immune response, and the raised antibodies could neutralize the virus in in vitro test.