ACE2 and viral infectious disease: The S protein plays an importantrole in viral infection as it binds to host cells during the firststep of virus invasion, which makes it a popular target for antibodyand vaccine design.3−7 The anchor of the receptor binding domain (RBD) of the S proteinto the human Angiotensin-converting enzyme 2 (ACE2) initiates theentry of the virus into the host cell8,9 (the RBD actuallybinds to the peptidase domain of ACE2, but for simplicity, we saythat it binds to ACE2).