ACE2 and infection: However, as the receptor-binding domain (RBD) of the spike protein (S) is crucial for infection [due to its interaction with the angiotensin-converting enzyme 2, ACE2, that is, the cellular receptor for SARS-CoV-2 (4)], the limited (85%) sequence identity (5) of the RBDs of SARS-CoV-2 and RaTG13 led to suspect the existence of an intermediate host.