Fig. 4: R1-32 binding resulted in destruction of SARS-CoV-2 spike structure.
a,b, Ligand-induced conformational change assays to probe the induction of post-fusion structures. a, Native spike (S-R) (7.09 µM) was incubated with molar excess of ACE2-Fc or antibodies for 1 h. Samples were analysed by western blotting to detect generation of the 55 kDa proteinase K-resistant core, which is a signature of the post-fusion S2 structure62. ACE2-Fc and class 1 antibodies B38 and rmAb23 induced post-fusion structures. b, Inhibition of conformational change by non-ACE2 competing antibodies were assayed by antibody pre-incubation (1 h) before further incubation (1 h) with ACE2-Fc. Only R1-32 was able to abolish fusogenic spike conformational change among the tested non-ACE2 competing antibodies. Representative data are shown from at least 3 independent experiments (a,b). The effects of ACE2-Fc and antibody binding on the structure of SARS-CoV-2 S-R spike after 1 h or 24 h incubations were assessed by negative-stain EM. c–e, Binding of ACE2-Fc (c), B38 (d) and rmAb23 (e) induced post-fusion structures that aggregate to form rosettes (examples are outlined by yellow circles) similar to our previous observations on the SARS-CoV-1 spike63. f,g, Binding of R1-32 Fab (f) or R1-32 (g) IgG to the S-R spike caused the spike to disintegrate into smaller structures (examples are outlined by red circles). h, Images for the S-R spike in the control experiment in which no ligand was added (intact spike examples are outlined by green circles). Scale bar, 100 nm. Representative data are shown from at least 2 independent experiments (c–h).
