SARS-CoV RBM ridge contains a Pro-Pro-Ala motif that is replaced by Gly-Val-Glu-Gly in SARS-CoV-2 (residues 482–485), yielding a more compact loop able to engage more interactions with proximal ACE2 residues (e.g., Ser19 and Gln24) (Shang et al., 2020b).