FIG 5.
The SARS-CoV-2 RBD interaction with hACE2 follows a Langmuir-based kinetic with time-independent monoexponential decay. (A) Multicycle experiment with SARS-CoV-2 RBD. hACE2-fc was immobilized on a protein A/G sensor chip, and SARS-CoV-2 RBD was injected in a concentration range of 3.9 to 1,000 nM. The KD was globally fitted with a 1:1 Langmuir-based interaction model. The kinetic parameters were determined with a KD of 21.3 nM, ka of 4.3 E + 5 ± 2.2 E + 2 [1/Ms], and kd of 9.1 E-3 ± 4.2 E-6 [1/s]. Chi2, 0.05 [RU2] (B) Test on secondary state reaction. hACE2 was immobilized on a protein A sensor surface, and 500 nM SARS-CoV-2 was injected at a constant concentration for increasing contact intervals. Dissociation starting point was aligned on the time scale. (C) SEC-HPLC using 5-μg/mL injections of SARS-CoV-2 RBD and hACE2 dimer. Column calibration was performed using protein standards of thyroglobulin (660 kDa, 5.78 min), γ-globulin (150 kDa, 7.52 min), ovalbumin (45 kDa, 8.52 min), and aprotinin (6.5 kDa, 11.12 min).