Fig. 6: Mode-of-action of 3D1 in SARS-CoV-2 neutralization.

a Spike-hACE2-mediated cell-cell membrane fusion assay. Representative images of SARS-CoV-2 spike (expressed in HEK293T cells with EGFP) mediated syncytium formation with hACE2-expressing cells from three independent replicates. Scale bars represent 200 µm. b Dose-dependent inhibition of 3D1 on the 6-HB conformation between HR1FC and HR2 peptides of SARS-CoV-2, representative of 3 independent trials. c 3D1 interferes with the hACE2 induced 6-HB formation, which is resistant to proteinase K, as visualized by Western-blot, as shown as a representative image from three independent experiments. d Dose-dependent binding of 3D1 to HR1FC but not to other conformations of the ectodomain of spike. Each titration point represents the mean of indenpendt triplicates. Standard deviations shown as error bars (n = 3). e Comparison of the HR1 conformation of 3D1-bound with those of HR1 in different fusion states. The signature-fold of ⁹⁵⁰DVVNQN⁹⁵⁵ is displayed as sticks, while other residues in the helical structures of HR1 in the prefusion and post-fusion states are shown as lines.