3.1.3  SARS-CoV2 receptor binding domain contains six amino acids providing favorable positions for binding to human ACE2
When compared to SARS-CoV SB, the motif binding the human ACE2 to the SARS-CoV 2 SB showed a relatively higher binding affinity for human ACE2 as indicated in smaller equilibrium dissociation constant (2.9 nM vs. 7.7 nM) [3]. Structural analysis has demonstrated that fourteen positions critically take part in the receptor-binding domain of the SARS-CoV SB that contain eight conserved (T402, Y436, Y440, N473, Y475, T486, G488, and Y491) positions and six semi-conserved (R426 to N448, Y442 to L464, L472 to F495, N479 to Q502, Y484 to Q507, and T487 to N510) substitutions with respect to the SARS-CoV 2 SB.