Fig. 2: aSA3-Fc is affected by mutations in the Omicron RBD.

a, b SPR binding kinetics of aSA3-Fc to SARS1 RBD (a) and WT SARS2 RBD (b) were monitored by the Biacore 8 K system. The actual responses (colored lines) and the data fitted to a 1:1 binding model (black dotted lines) are shown. c The neutralizing activities of aSA3-Fc against SARS1 and WT SARS2. Pseudovirus neutralization assays were performed to characterize the neutralizing activities of aSA3-Fc against SARS1 and WT SARS2 pseudoviruses, while PRNT was conducted to assess the neutralizing activities of aSA3-Fc against authentic WT SARS2. d ELISA results for the binding of aSA3-Fc to the RBD of WT SARS2 and its major variants. EC₅₀ values were calculated by fitting the OD₄₅₀ values to a sigmoidal dose-response curve and shown in the brackets. e–g SPR binding kinetics of aSA3-Fc to the RBD of Omicron BA.1 (e), BA.2 (f), and BA.5 (g). The actual responses (colored lines) and the data fitted to a 1:1 binding model (black dotted lines) are shown. h The structure of aSA3:SARS1 RBD complex superimposed on the structure of SARS2 RBD (PDB: 6M0J). The six mutation sites shared by the RBDs of Alpha, Beta, Gamma, Kappa, Lambda, Delta, and Delta plus are marked in blue, the aSA3 footprints are marked in green. i The aSA3 footprints (green) and mutation sites of BA.1, BA.2, and BA.5 (marine) on RBD. j The neutralization properties of aSA3-Fc against authentic Beta, Delta and BA.1. k The neutralization properties of aSA3-Fc against pseudotyped BA.1, BA.2, and BA.5. The IC₅₀ values were calculated by fitting the inhibition rates against antibody concentrations with a sigmoidal dose-response curve. Error bars indicate the means ± SD from three (pseudovirus) or two replicates (authentic virus). l R408S mutation present on BA.2 and BA.5 (R408 of SARS2 RBD corresponds to R395 of SARS1 RBD) may reduce the binding of aSA3 to the α-helix on the concave surface of RBD. Black dotted lines indicate hydrogen bonds and salt bridges.