Fig. 5
RBD binding affinity of the sdAb candidates. (A) Pie chart of RBD sdAbs’ affinity and expression in E. coli. High expression indicated more than 5 mg sdAbs protein could be purified from 1 L of E. coli broth. (B) RBD binding affinity analysis of the sdAb candidates by ELISA. (C) EC50 of the sdAb candidates binding to RBD. The EC50 is the concentration of sdAbs that gives a half-maximal RBD-binding response. (D) Five highest affinity RBD sdAb candidates. (E)` The amino acid sequence of the five highest affinity RBD sdAb candidates. (F) The binding affinity of sdAb39 and ACE2 to wild-type RBD. The upper panel: the association and dissociation of the response curves of each sample. Fc-tagged SARS-CoV-2 RBDs were loaded onto the surface of Protein A biosensors. A series of concentrations of each sample were used. The lower panel: Kd of each sample was fitted based on the experimental data