Table 1. Kinetic Parameters Obtained from SPR Assaysa.
| variant | ka (105 M–1 s–1) | kd (10–4 s–1) | KD (nM)b |
|---|---|---|---|
| RBDWT | 6.6 ± 2.0 | 93.4 ± 1.7 | 15.0 ± 4.1 |
| RBDB.1.1.7 (alpha) | 9.0 ± 3.0 | 15.5 ± 0.1 | 1.8 ± 0.5 |
| RBDB.1.351 (beta) | 9.0 ± 2.7 | 40.9 ± 1.3 | 4.8 ± 1.4 |
| RBDP.1 (gamma) | 9.0 ± 3.4 | 27.8 ± 0.9 | 3.3 ± 1.0 |
| spike trimerWT | 0.7 ± 0.2 | 4.8 ± 0.8 | 6.7 ± 1.3 |
| spike trimerB.1.1.7 (alpha) | 0.8 ± 0.2 | 1.5 ± 0.1 | 1.9 ± 0.2 |
| spike trimerB.1.351 (beta) | 1.6 ± 0.9 | 2.1 ± 0.7 | 1.4 ± 0.3 |
| spike trimerP.1 (gamma) | 1.2 ± 0.5 | 2.4 ± 0.5 | 2.1 ± 0.3 |
Equilibrium dissociation constants (KD’s) calculated for RBD and its variants in complex with the dimeric hACE2 protein. Experimental KD values were also measured using a trimeric spike protein and its variants for interacting with the dimeric form of hACE2 (residues 18–740) fused with a human IgG1 Fc tag at the C-terminus. The mutations in each spike constructions are shown in parentheses: RBDB.1.1.7 (N501Y); RBDB.1.351 (K417N, E484K, and N501Y); RBDP.1 (K417T, E484K, and N501Y); spike trimerB.1.1.7 (H69-V70del, Y144del, N501Y, A570D, D614G, P681H, T716I, S982A, and D1118H); spike trimerB.1.351 (L18F, D80A, D215G, L242-A243-L244del, R246I, K417N, E484K, N501Y, D614G, and A701V); spike trimerP.1 (L18F, T20N, P26S, D138Y, R190S, K417T, E484K, N501Y, D614G, H655Y, T1027I, and V1176F). In spike trimer constructions, the proline substitutions (F817P, A892P, A899P, A942P, K986P, and V987P) were introduced to stabilize the trimeric prefusion state of the SARS-CoV-2 spike protein, and alanine substitutions (R683A and R685A) were introduced to abolish the furin cleavage site. More details are shown in Table S7. The SPR assays were performed in three biological replicates.
KD = kd/ka.