ACE2 and COVID-19: The virus which causes COVID-19, named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first enters into host cells by binding to the cellular receptor angiotensin-converting enzyme 2 (ACE2) via receptor-binding domain (RBD) interacting with the C-terminal domain of SARS-CoV-2 spike protein (S) 1.