Fig. 1: Biochemical and structural characterization of neutralizing synthetic nanobodies (sybodies).

a Summary of the characterization. Yield refers to purification from 1 L of culture. b Neutralization assay. SARS-CoV-2 pseudoviruses were preincubated with different concentrations of sybodies before infection of VeroE6-hACE2 cells. The rate of infection was measured by FACS. IC₅₀ was obtained by Sigmoidal fitting of the percentage of neutralization. Mean ± standard deviation are plotted (n = 3 or 4 independent experiments). Error bars are omitted where, in rare cases, available data points are less than three due to experimental design on concentration replicates. Color coding of the sybodies is as indicated. c The overall structure of SR4 (pink cartoon) in complex with RBD (green surface), which resembles a short backrest high chair. The binding surface is highlighted red. d SR4 CDR1 (yellow), CDR2 (magenta), and CDR3 (cyan) all contribute to the binding. Note that Tyr37 is a framework residue. e The overall structure of the MR17 (pink cartoon) in complex with RBD (green surface). The binding surface is highlighted red. f The overlap (magenta) between the SR4 (blue) and MR17 (red) interacting surfaces on RBD. g All three CDRs contribute to the binding with the receptor-binding domain (RBD) (green). Lys65 and Tyr60 are from the framework region. CDRs are color-coded as indicated in d. Dashed lines indicate H-bonding or salt bridges between atoms that are <4.0 Å apart. Black texts label sybody residues and gray texts label RBD residues. Source data for b are provided as a Source data file. CDR complementarity determining region, FACS fluorescence-activated cell sorting, RBD receptor-binding domain.