The mechanism of interactions with peptidases (aminopeptidase APN, ACE2, DPP4) as a cellular receptor for most coronaviruses is not known. Indeed, the binding of coronaviruses to their receptor is not enough and S protein on the surface of the virus must undergo proteolytic maturation. Coronaviruses do not use the catalytic activity of peptidases serving as receptors for this maturation but enter after the action of proteases located close to the receptors. The binding of SARS-CoV to its ACE2 receptor is followed by internalization and decrease in ACE2 enzyme activity on the cell surface, which may partly explain the severity of SARS-CoV infections [25].