Fig. 1: aSA3 cross-reacts with SARS1 and WT SARS2 by targeting an epitope on RBD core.
a, b The binding kinetics of aSA3 to SARS1 RBD (a) and WT SARS2 RBD (b) were monitored by the Biacore 8K system. The actual responses (colored lines) and the data fitted to a 1:1 binding model (black dotted lines) are shown. KD, equilibrium dissociation constant; ka, association constant; kd, dissociation constant. c The blocking abilities of aSA3 against the interaction between ACE2-Fc and SARS1/2 RBD were tested by competitive ELISA. SARS1 RBD-tr2 or WT SARS2 RBD-tr2 were coated on the plate and incubated with a mixture of 20 nM ACE2-Fc with serial dilutions of aSA3. Bound ACE2-Fc was detected with HRP conjugated anti-IgG1 Fc antibody. Error bars indicate the means ± SD from two independent experiments. d The neutralizing activities of aSA3 against pseudotyped SARS1 and WT SARS2. The IC50 values of the pseudovirus neutralization assay were calculated by fitting the inhibition rates against antibody concentrations with a sigmoidal dose-response curve. Error bars indicate the means ± SD from triplicates. e The overall structure of aSA3 (hotpink) bound to SARS1 RBD (gray) using cartoon presentation. f, g Superposition analysis of aSA3 onto one “up” RBD (f) and one “down” RBD (g) in the cryo-EM structure of the trimeric spike of SARS2 (PDB: 7KMZ). h Structure alignment of the aSA3:SARS1 RBD complex with the ACE2:SARS1 RBD complex (PDB: 2AJF). The dotted box marks the region where FR2 of aSA3 clashes with ACE2. i Zoom-in view of the interaction interface of aSA3 and SARS1 RBD. Interacting residues are shown as sticks, and dotted lines indicate hydrogen bonds and salt bridges. j Sequence alignment of the SARS1 and SARS2 RBDs. Identical residues are marked with yellow shading, and residues interacting with aSA3 are indicated with red circles.
