Structures of potent and convergent neutralizing antibodies bound to the SARS-CoV-2 spike unveil a unique epitope responsible for exceptional potency

Understanding the mechanism of neutralizing antibodies (NAbs) against SARS-CoV-2 is critical for effective vaccines and therapeutics development. We recently reported an exceptionally potent NAb, BD-368-2, and revealed the existence ofVH3-53/VH3-66convergent NAbs in COVID-19. Here we report the 3.5-Å cryo-EM structure of BD-368-2’s Fabs in complex with a mutation-induced prefusion-state-stabilized spike trimer. UnlikeVH3-53/VH3-66NAbs, BD-368-2 fully blocks ACE2 binding by occupying all three receptor-binding domains (RBDs) simultaneously, regardless of their “up” and “down” positions. BD-368-2 also triggers fusogenic-like structural rearrangements of the spike trimer, which could impede viral entry. Moreover, BD-368-2 completely avoids the common epitope ofVH3-53/VH3-66NAbs, evidenced by multiple crystal structures of their Fabs in tripartite complexes with RBD, suggesting a new way of pairing potent NAbs to prevent neutralization escape. Together, these results rationalize a unique epitope that leads to exceptional neutralization potency, and provide guidance for NAb therapeutics and vaccine designs against SARS-CoV-2.