Fig 1: Binding affinity of gRBD, dRBD, and commercial RBDs of SARS-CoV-2 to ACE2, the receptor of SARS-CoV-2. The samples of 100 ng of plant-produced gRBD, dRBD, and commercially available (A) recombinant SARS-CoV-2 S protein RBD (amino acids Arg319–Phe541, with a C-terminal 8×His tag, expressed in 293E cells, cat. no. 793606, BioLegend, USA), or (B) SARS-CoV-2 spike protein (RBD) coronavirus active protein (amino acids Arg319–Phe541, produced in baculovirus–insect cells, cat. no. MBS2563882, MyBioSource, San Diego, CA, USA) were incubated on plates coated with ACE2. After incubation, anti-SARS-CoV-2 spike RBD polyclonal antibodies were added into each well and detected with rabbit IgG conjugated with HRP. Each point on the graph was derived from three replica for each dilution. Data are shown as mean ± standard error of the mean (SEM) of triplicates in each sample dilution. Statistical significance (p < 0.05) was calculated using the one-way ANOVA test with Tukey’s multiple comparisons. p value for each group is shown in parentheses. ** p < 0.01, *** p < 0.001; OD—optical density; Kd—dissociation constant.