Strategy for the Construction of SARS-CoV-2 S and N Recombinant Proteins and Their Immunogenicity Evaluation

This study reports the construction, expression, and purification of synthetic SARS-CoV-2 spike (S) and nucleoprotein (N) containing immunodominant epitopes. The pET28aS_epit construct included epitopes 287-317, 402, 507, 524-598, and 601-640, while the pET28aN_epit construct included residues 42-62, 153-172, and 355-401. Commercial sequences of both proteins were used as controls. The four constructs were expressed using the Escherichia coli BL21(DE3) star strain at 37 °C. The results show that the S protein constructs were insoluble, unlike the N protein constructs. Both recombinant proteins induced immune responses in mice and were recognized by antibodies present in sera from COVID-19-positive and/or SARS-CoV-2-vaccinated humans. No significant differences in immune recognition were observed between our constructs and the commercially available proteins. In conclusion, S_epit and N_epit could be promising starting points for the development of new strategies based on immunological reactions for the control of SARS-CoV-2 infections.