Fig. 3. Ab 2-7 can only bind as an scFv and Ab 12 competes with ACE2.

A Cryo-EM reconstruction of unbound S-D614G with one RBD in the up conformation (3.0 Å). Coloring is the same as in Fig. 2. The inset at the top right shows that Ab 2-7 would clash with the “down” RBD of the neighboring spike protomer (green cryo-EM reconstruction, filtered to 6 Å). The inset below shows Ab 2-7 modeled as a Fab, wherein the CH region would clash with the spike NTD (blue cryo-EM reconstruction, filtered to 6 Å). Clashes are indicated as white arrows. B Overlay of ACE2 bound to the RBD confirms that Ab 12 directly competes for the receptor binding motif (RBM). Ab 2-7 binds the conserved RBD core and does not directly compete with ACE2. Clashes are indicated as white arrows.