Fig. 2.

Cartoon representation showing the pre- to post-fusion transition of the SARS-CoV S glycoprotein. The ªdownº to ªupº transition of the receptor-binding domain (CTD1) allows receptor binding. The binding to ACE2 opens up CTD1 and CTD2, promotes the disassociation of the S1-ACE2 complex from the S1/S2 cleaved S glycoprotein, induces the pre- to post-fusion transition of the S2 subunit, and initiates the membrane fusion. Spike (S); angiotensin-converting enzyme (ACE); severe acute respiratory syndrome (SARS)

From Song W. PLOS Pathogens 10.1371/journal.ppat.1007236 with permission