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. 2021 Oct 21;11(4):778–784. doi: 10.3390/clinpract11040093

Figure 1.

Figure 1

SARS-CoV-2 structure and binding schematic. (A) Native resting state of the ACE-II receptor on the host cell surface. (B) Spike protein binding to the ACE-II receptor. (C) Viral fusion with the host cell membrane. Host cell proteases cleave the spike protein into S1 and S2 subunits. S1 is responsible for binding to ACE-II, while S2 is responsible for viral fusion and entry. Upon S1 binding ACE-II, the HR 1 and 2 subunits form the 6-helix bundle (6-HB) in order to bring the viral particle close to the host cell to allow for fusion and entry [11].