Fig. 5.

Comparison of receptor binding affinity and cell entry efficiency of SARS-CoV-2 and SARS-CoV. (A) Spike pull-down assay using hACE2 as the bait and cell-associated coronavirus spike molecules as the targets. (Top) Cell-expressed coronavirus spike molecules including SARS-CoV-2 spike, SARS-CoV-2 spike containing a mutant furin site as in Fig. 2A, SARS-CoV spike, and MERS-CoV spike. These spike molecules all contain a C-terminal C9 tag. (Middle) Pull-down result using His₆-tagged hACE2. (Bottom) Pull-down result using Fc-tagged hACE2. (B) RBD pull-down assay using Fc-tagged hACE2 as the bait and soluble coronavirus RBDs as the targets. These RBD molecules all contain a C-terminal His₆ tag. (C) (Left) Entry of SARS-CoV-2 and SARS-CoV pseudoviruses into three types of target cells. (Right) Western blot of SARS-CoV-2 and SARS-CoV pseudoviruses used in the cell entry assay.