Figure 1:

ACE2-mediated SARS-CoV-2 viral entry via the membrane fusion pathway. SARS-CoV-2-spike binds to ACE2 on the target cell surface (step A), after which furin cleaves SARS-CoV-2-spike at the S1/S2 boundary (step B). Furin may also cleave the spike protein at the S1/S2 boundary during viral production, prior to virus release into the extracellular space. TMPRSS2 cleaves the S2 protein at the S2’ site (step C), which allows the insertion of hydrophobic amino acid residues in the activated S2 subunit into the plasma membrane (step D), facilitating membrane fusion between the viral envelope and the host cell plasma membrane (step E).