Marit van Gils
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Researcher at Amsterdam UMC
The protective efficacy of neutralizing antibodies (nAbs) elicited during natural infection with SARS-CoV-2 and by vaccination based on its spike protein has been compromised with emergence of the recent SARS-CoV-2 variants. Residues E484 and K417 in the receptor-binding site (RBS) are both mutated in lineages first described in South Africa (B.1.351) and Brazil (B.1.1.28.1). The nAbs isolated from SARS-CoV-2 patients are preferentially encoded by certain heavy-chain germline genes and the two most frequently elicited antibody families (IGHV3-53/3-66 and IGHV1-2) can each bind the RBS in two different binding modes. However, their binding and neutralization are abrogated by either the E484K or K417N mutation, whereas nAbs to the cross-reactive CR3022 and S309 sites are largely unaffected. This structural and functional analysis illustrates why mutations at E484 and K417 adversely affect major classes of nAbs to SARS-CoV-2 with consequences for next-generation COVID-19 vaccines.
Coronaviruses have caused several epidemics and pandemics including the ongoing coronavirus disease 2019 (COVID-19). Some prophylactic vaccines and therapeutic antibodies have already showed striking effectiveness against COVID-19. Nevertheless, concerns remain about antigenic drift in SARS-CoV-2 as well as threats from other sarbecoviruses. Cross-neutralizing antibodies to SARS-related viruses provide opportunities to address such concerns. Here, we report on crystal structures of a cross-neutralizing antibody CV38-142 in complex with the receptor binding domains from SARS-CoV-2 and SARS-CoV. Our structural findings provide mechanistic insights into how this antibody can accommodate antigenic variation in these viruses. CV38-142 synergizes with other cross-neutralizing antibodies, in particular COVA1-16, to enhance neutralization of SARS-CoV-2 and SARS-CoV. Overall, this study provides valuable information for vaccine and therapeutic design to address current and future antigenic drift in SARS-CoV-2 and to protect against zoonotic coronaviruses.
Cell Reports, 2020-09-29
IGHV3-53-encoded neutralizing antibodies are commonly elicited during SARS-CoV-2 infection and target the receptor-binding domain (RBD) of the spike (S) protein. Such IGHV3-53 antibodies generally have a short CDR H3 due to structural constraints in binding the RBD (mode A). However, a small subset of IGHV3-53 antibodies to the RBD contain a longer CDR H3. Crystal structures of two IGHV3-53 neutralizing antibodies here demonstrate that a longer CDR H3 can be accommodated in a different binding mode (mode B). These two classes of IGHV3-53 antibodies both target the ACE2 receptor binding site, but with very different angles of approach and molecular interactions. Overall, these findings emphasize the versatility of IGHV3-53 in this common antibody response to SARS-CoV-2, where conserved IGHV3-53 germline-encoded features can be combined with very different CDR H3 lengths and light chains for SARS-CoV-2 RBD recognition and virus neutralization. ### Competing Interest Statement Amsterdam UMC previously filed a patent application that included SARS-CoV-2 antibodies COVA2-04 and COVA2-39 (Brouwer et al., 2020).
Most antibodies isolated from COVID-19 patients are specific to SARS-CoV-2. COVA1-16 is a relatively rare antibody that also cross-neutralizes SARS-CoV. Here we determined a crystal structure of COVA1-16 Fab with the SARS-CoV-2 RBD, and a negative-stain EM reconstruction with the spike glycoprotein trimer, to elucidate the structural basis of its cross-reactivity. COVA1-16 binds a highly conserved epitope on the SARS-CoV-2 RBD, mainly through a long CDR H3, and competes with ACE2 binding due to steric hindrance rather than epitope overlap. COVA1-16 binds to a flexible up conformation of the RBD on the spike and relies on antibody avidity for neutralization. These findings, along with structural and functional rationale for the epitope conservation, provide a blueprint for development of more universal SARS-like coronavirus vaccines and therapies. ### Competing Interest Statement Amsterdam UMC previously filed a patent application on the SARS-CoV-2 antibody COVA1-16 described here.