Extended Data Figure 3:

Comparison of human ACE2 binding by SARS-CoV RBD, SARS-CoV-2 wild-type RBD, and SARS-CoV-2 chimeric RBD. (a) Buried surface areas at SARS-CoV RBM/human ACE2 and SARS-CoV-2 RBM/human ACE2 interfaces. In the crystals for both SARS-CoV RBD/ACE2 complex and chimeric RBD/ACE2 complex, two copes of each complex were present in one asymmetric unit. Numbers for both copies of the complexes are shown. The interaction between Arg439 on the side loop in the RBM and Glu329 from human ACE2 was excluded in the calculation of buried surface area for SARS-CoV-2. (b) List of contact residues from RBM and ACE2 that are directly involved in RBM/ACE2 binding. The engineered Arg439 in the chimeric RBD is in orange. Contact residues from SARS-CoV RBM/ACE2 are taken from PDB 2AJF. (c) Binding affinities between the RBDs and human ACE2 as measured using surface plasmon resonance.