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. 2022 Jun 6;8:53. doi: 10.1038/s41421-022-00419-w

Fig. 6. Proposed mechanism by which CTSL promotes SARS-CoV-2 infection.

Fig. 6

SARS-CoV-2 S contains S1 and S2 subunits. CS-1 is located in the NTD of the S1 subunit, and CS-2 is located near the S1/S2 site. CTSL cleaves the SARS-CoV-2 S protein: (1) By binding with the S protein on the surface of SARS-CoV-2, CTSL cleaves S at CS-1 and CS-2 sites. (2) The cleavage increases the dynamics of the RBD and makes it accessible to ACE2 for binding. (3) CTSL cleaves CS-2 site to separate S1 and S2 subunits to expose the S2 subunit for membrane fusion. (4) The virus fuses with the membrane of target cell, and the viral genetic material is released into the host cell.