ACE2 and severe acute respiratory syndrome: The entry of pathogenic coronavirus into host cells is enabled by the interaction of the viral spike protein (S1) with a variety of cellular receptors in the plasma membrane of host cells, like the angiotensin-converting enzyme 2 (ACE2) in SARS-CoV infection and SARS-CoV-2 and the dipeptidyl-peptidase 4 (DPP4) in MERS-CoV infection.7