RBDwt and RBDmut kinetics by Bio-Layer Interferometry (BLI)
The analysis of binding kinetics of RBDWT and RBDTRIP to ACE2-mFc was performed by Bio-Layer Interferometry (BLI) using an Octet RED96e (Fortebio) instrument. High precision Streptavidin (SAX, ForteBio, Fremont, CA, USA) biosensors were saturated with 7.5 µg/ml biotinylated ACE2-mFc in BLI assay buffer (PBS, 0.1% BSA, 0.02% Tween 20) for 10 min. RBDWT and RBDTRIP were prepared as twofold serial dilution (typically 50, 25, 12.5, 6.25 and 3.125 nM) in BLI assay buffer plus buffer blanks. Kinetic values were calculated by ForteBio data analysis software using a 1:1 binding model.