Fig. 4: Surface expression of Spike mutants.

A Spike surface expression of WT and ΔTMD controls was analyzed by flow cytometry. HEK293T cells were transfected with plasmids encoding the corresponding S protein alongside a constitutively GFP-expressing plasmid. After 48 h, cells were stained with an anti-RBD antibody. Levels of the surface SARS-CoV-2 S protein (red) and GFP (green) were analyzed by flow cytometry. B Relative surface expression of all Spike mutants tested in this assay. GFP was used as a transfection control. The figure shows the percentage of SARS-CoV-2 S protein vs GFP signal ratio. Samples were normalized to the SARS-CoV-2 S protein WT. The significative p-values (<0.05) for individual one-sample t-tests vs. WT are indicated above each bar. Three independent biological replicates were performed.