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

## TL;DR

This study creates and tests SARS-CoV-2 spike and nucleoprotein fragments to evaluate their ability to trigger immune responses in mice and humans.

## Contribution

The study introduces new recombinant SARS-CoV-2 S and N protein constructs with immunodominant epitopes and evaluates their immunogenicity.

## Key findings

- The S protein constructs were insoluble, while the N protein constructs were soluble.
- Both recombinant proteins induced immune responses in mice and were recognized by antibodies from COVID-19-positive and vaccinated humans.
- No significant differences in immune recognition were found between the constructs and commercial proteins.

## Abstract

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.