Immunodominant B cell epitope in SARS-CoV-2 RBD comprises a B.1.351 and P.1 mutation hotspot: implications for viral spread and antibody escape

Abstract

Recent SARS-CoV-2 variants pose important concerns due to their higher transmissibility (1) and escape (2) from previous infections or vaccine-induced neutralizing antibodies (nAb). The receptor binding domain (RBD) of the Spike protein is a major nAb target (3), but data on its B cell epitopes are still lacking. Using a peptide microarray, we identified an immunodominant epitope (S415-429) recognized by 68% of sera from 71 convalescent Brazilians infected with the ancestral variant. In contrast with previous studies, we have identified a linear IgG and IgA antibody binding epitope within the RBD. IgG and IgA antibody levels for this epitope positively correlated with nAb titers, suggesting a potential target of antibody neutralizing activity. Interestingly, this immunodominant RBD region harbors the mutation hotspot site K417 present in P.1 (K417T) and B.1.351 (K417N) variants. In silico simulation analyses indicate impaired RBD binding to nAb in both variants and that glycosylation in the B.1.351 417N could further hinder antibody binding as compared to the K417T mutation in P.1. This is in line with published data showing that nAb from either convalescents or anti-CoV-2 vaccinees are less effective towards B.1.351 than for P.1. Our data support the occurrence of immune pressure and selection involving this immunodominant epitope that may have critically contributed to the recent COVID-19 marked rise in Brazil and South Africa, and pinpoint a potential additional immune escape mechanism for SARS-CoV-2.