a, Side and top views of cryo-EM 3D reconstructions of VH3 B01 + Secto (PDB 7JWB), shown with individual VH domain densities of VH3 B01 fit with PDB 3P9W (VH scaffold; orange cartoon). A total of three VH domains, each bound to an RBD of the Spike trimer, are resolved. The 3D model of Secto was fit with a reference structure (PDB 6X2B, with additional rigid body fit of the individual RBDs; blue cartoon) and shows RBDs in a distinct two ‘up’, one ‘down’ conformation. The cryo-EM map was low-pass-filtered to 6 Å. b, View of the epitope (site B) of one VH domain from VH3 B01. Site B overlays directly with the ACE2 binding site (yellow surface; contacts defined as RBD residues within 8 Å of an ACE2 residue from PDB 6M0J).