Fig. 4: ACE2 receptor binding the SARS-Cov-2 virus.

The initial step of SARS-Cov-2 viral entry during the infection is the binding of the viral trimeric spike protein (cleaved into S1 and S2 subunits, the former of which contains the receptor-binding domain, RBD) to the dimeric human receptor angiotensin-converting enzyme 2 (ACE2) which is here represented in the complex with the membrane protein that it chaperones, BoAT1. ACE2 is formed by an N-terminal peptidase domain (PD) and the C-terminal collectrin-like domain (CLD). ACE2 shows a closed and an open (depicted) conformation at the PD level of contact; however, only the closed conformation binds the RBD of SARS-Cov-2. The structure shown was obtained by Cryo-EM at 2.9 Å resolution (PBD = 6M17) was released on 11 March 2020 from Yan et al.⁶.