ACE2 and viral infectious disease: Previous studies have shown that the human angiotensin-converting enzyme 2 (ACE2) is a functional cellular receptor for SARS-CoV-2.2,13 ACE2 is a type I trans-membrane protein with a large N-terminal ecto-domain, which can be further divided into a peptidase domain (PD) possessing the carboxypeptidase activity and a collectrin-like domain (CLD) mediating ACE2 homodimerization.14,15 During virus infection, however, ACE2 has been shown to be exploited by multiple coronaviruses, including SARS-CoV, SARS-CoV-2, and human coronavirus NL63, for cell entry.2,13,16–18