fig 1. Binding of recombinant SARS-CoV-2 S spike protein to biotinylated human ACE2 protein captured onto a streptavidin-coated sensor chip. The S protein was applied at 12.5 to 200 nM and gave a kinetic-derived affinity constant (Kd) of 35.6 nM.
fig 2. Binding of recombinant spike protein (20 nM) to surface-bound (streptavidin-captured) biotinylated ACE2 is attenuated by pre-incubation of the spike protein with a 10-fold excess of soluble, non-biotinylated ACE2 (200 nM).