Identification of immunodominant epitopes on nucleocapsid and spike
proteins of the SARS-CoV-2 in Iranian COVID-19 patients
Abstract
Given the emergence of SARS-CoV-2 virus as a life-threatening pandemic,
identification of immunodominant epitopes of the viral structural
proteins, particularly the nucleocapsid (NP) protein and receptor
binding domain (RBD) of spike protein, is important to determine targets
for immunotherapy and diagnosis. In this study, epitope screening was
performed using a panel of overlapping peptides spanning the entire
sequences of the RBD and NP proteins of SARS-CoV-2 in the sera from 66
COVID-19 patients and 23 healthy subjects by enzyme-linked immunosorbent
assay (ELISA). Also, three non-overlapping peptides belonging to the S2
domain of spike protein were assessed. Our results showed that while
reactivity of patients’ sera with reduced recombinant RBD protein was
significantly lower than the native form of RBD (p<0.001), no
significant differences were observed for reactivity of patients’ sera
with reduced and non-reduced NP protein. Pepscan analysis revealed weak
to moderate reactivity towards different RBD peptide pools, which was
more focused on peptides encompassing aa 181-223 of RBD. NP peptides,
however, displayed strong reactivity with a single peptide covering aa
151-170. These findings were confirmed by peptide depletion experiments
using both ELISA and Western blotting. Altogether, our data suggest the
involvement of mostly conformational disulfide bond-dependent
immunodominant epitopes in RBD-specific antibody response, while the IgG
response to NP is dominated by linear epitopes. Identification of
antigenic epitope in NP and RBD of SARS-CoV-2 could provide important
advances for the development of passive and active immunotherapy as well
as diagnostic tools for the control of COVID-19 infection.