![]() SP, signal peptide FP, fusion peptide HR, heptad repeat domain TM, transmembrane domain CP, cytoplasmic domain. ![]() a Schematic representation of SARS-CoV-2 S protein and the location of S1/S2 and S2′ cleavage site. The function of furin cleavage site in SARS-CoV-2-S mediated fusion. Therefore, it has been speculated that this unique FCS may provide a gain-of-function, making SARS-CoV-2 easily enter into the host cell for infection, thus efficiently spreading throughout the human population, compared to other lineage B betacoronaviruses. 3 Coincidentally, phylogenetic analysis of SARS-CoV-2 identified an insertion of RRAR (FCS) at the S1/S2 site of SARS-CoV-2-S, which is absent in SARS-CoV and other SARS-related coronaviruses (SARSr-CoVs), particularly RaTG13, which has 96% identity of its genomic sequence to that of SARS-CoV-2 (Fig. Previous studies have shown that an insertion of FCS consisting of multiple basic amino acids in the cleavage site of the haemagglutinin (HA) is associated with high virulence of influenza viruses. Consisting of S1 receptor-binding subunit and S2 fusion subunit, CoV-S needs to be primed through cleavage at S1/S2 site and S2′ site in order to mediate the membrane fusion (Fig. Therefore, the fusion capacity of the CoV-S is a leading indicator of infectivity of the corresponding virus. ![]() No matter what path it chooses, the final step of viral entry involves the release of RNA into the cytoplasm for replication. A coronavirus (CoV) infects the target cell by either cytoplasmic or endosomal membrane fusion. ![]()
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