SARS-coronavirus (CoV) is a zoonotic agent derived from rhinolophid bats, in which a plethora of SARS-related, conspecific viral lineages exist. Whereas the variability of virulence among reservoir-borne viruses is unknown, it is generally assumed that the emergence of epidemic viruses from animal reservoirs requires human adaptation. To understand the influence of a viral factor in relation to interspecies spillover, we studied the papain-like protease (PLP) of SARS-CoV. This key enzyme drives the early stages of infection as it cleaves the viral polyprotein, deubiquitinates viral and cellular proteins, and antagonizes the interferon (IFN) response. We identified a bat SARS-CoV PLP, which shared 86% amino acid identity with SARS-CoV PLP, and used reverse genetics to insert it into the SARS-CoV genome. The resulting virus replicated like SARS-CoV in Vero cells but was suppressed in IFN competent MA-104 (3.7-fold), Calu-3 (2.6-fold) and human airway epithelial cells (10.3-fold). Using ectopically-expressed PLP variants as well as full SARS-CoV infectious clones chimerized for PLP, we found that a protease-independent, anti-IFN function exists in SARS-CoV, but not in a SARS-related, bat-borne virus. This PLP-mediated anti-IFN difference was seen in primate, human as well as bat cells, thus independent of the host context. The results of this study revealed that coronavirus PLP confers a variable virulence trait among members of the species SARS-CoV, and that a SARS-CoV lineage with virulent PLPs may have pre-existed in the reservoir before onset of the epidemic. Author summary Novel detection and sequencing technologies have greatly improved our knowledge of virus diversity in nature. Metaviromic screening of zoonotic animal reservoirs has become an established approach in pathogen surveillance and pandemic preparedness research. However, knowledge of viral genomes and host-associated viromes is insufficient to predict zoonotic spillover events of reservoir-borne viruses. Phenotypic characterization of important viral functions will be necessary to identify virulence traits that determine the potential of viral emergence. As proof-of-principle, the present study demonstrates relevant functional differences between one of the main host immune antagonists of bat-borne viruses that belong to the same virus species as the epidemic agent of SARS. The antagonist, the papain-like protease, shows double action against IFN-mediated antiviral effects in epidemic SARS-coronavirus (binding and processing of ubiquitin), whereas the homologous protein in bat-borne viruses has only the processing function. This finding is surprising as the papain-like protease is a highly conserved protein domain that was not expected to vary among conspecific coronaviruses. PLP function may represent a variable virulence trait among reservoir-borne viruses. The preformed virulence of the primordial genetic lineage may have supported the emergence of SARS-CoV as a human epidemic agent.
【초록키워드】 viruses, Coronaviruses, coronavirus, pandemic, SARS-CoV, knowledge, Genome, Genetic, variant, Infection, Proteins, virus, genetics, immune, Antiviral effect, Papain-like protease, Protein, Epidemic, pathogen, Surveillance, cells, zoonotic, Research, Lineage, CoV, IFN, novel, virulence, homologous, early stage, predict, bats, Calu-3, function, binding, Amino acid, cellular, viral genome, identity, SARS-coronavirus, enzyme, domain, Variability, plethora, reservoir, clone, virulent, polyprotein, Vero Cell, antagonist, Host, PLP, approach, Cell, event, independent, the epidemic, sequencing technology, resulting, identify, conserved, supported, functional, determine, suppressed, the interferon, replicated, human airway epithelial, expected, competent, cleave, assumed, viral lineage, zoonotic spillover, 【제목키워드】 Papain-like protease, virulence, SARS-coronavirus, determine,