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Fig. 1 | Animal Diseases

Fig. 1

From: Roles of host proteases in the entry of SARS-CoV-2

Fig. 1

Experimentally observed host protease cleavage sites in S of SARS-CoV-2, SARS-CoV and MERS-CoV. A. The S is divided into two portions: S1 and S2. S1 contains the receptor-binding domain (RBD) where the receptor-binding motif (RBM) interacts with the functional receptor (ACE2 or DPP4). The S2 domain contains the fusion domain, which is responsible for viral entry into the cell. In betacoronavirus entry studies, two cleavage sites have been observed as S1/S2 which is cleaved to cause a conformational change to facilitate binding to the functional receptor and S2’ which is cleaved to expose the fusion domain to allow for viral entry. The S2’ site is highly conserved among all coronaviruses and is cleaved by TMPRSS2. (a) In SARS-CoV-2, the S1/S2 cleavage site can be cleaved by host furin and trypsin, and two cathepsin L cleavage sites have been observed in S1 region as pictured. (b) SARS-CoV is unable to be cleaved by host furin but has been observed to be cleaved at the S1/S2 site experimentally by trypsin (Kim et al. 2022b). In addition to TMPRSS2 cleavage at S2’ site, human airway trypsin-like protease (HAT) has also been experimentally observed to have cleavage activity at the site. (c) MERS-CoV S is able to be cleaved by the same proteases as SARS-CoV-2 in the S1/S2 and S2’ sites. B. The multibasic arginine (R) resides observed in S of SARS-CoV-2 and MERS-CoV in the S1/S2 region allow for the cleavage of host furin, which shows a specificity for the motif RXXR. S2’ is highly conserved among coronaviruses, as it is responsible for exposing the fusion domain to allow for cell entry

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