SARS-CoV-2 is a novel coronavirus first identified in December 2019. Notable features make SARS-CoV-2 distinct from most other previously-identified Betacoronaviruses, including the receptor binding domain of SARS-CoV-2 and a unique insertion of twelve nucleotide or four amino acids (PRRA) at the S1/S2 boundary. In this study, we identified two deletion variants of SARS-CoV-2 that either directly affect the polybasic cleavage site itself (NSPRRAR) or a flanking sequence (QTQTN). These deletions were verified by multiple sequencing methods. In vitro results showed that the deletion of NSPRRAR likely does not affect virus replication in Vero and Vero-E6 cells, however the deletion of QTQTN may restrict late phase viral replication. The deletion of QTQTN was detected in 3 of 68 clinical samples and half of 24 in vitro isolated viruses, whilst the deletion of NSPRRAR was identified in 3 in vitro isolated viruses. Our data indicate that (i) there may be distinct selection pressures on SARS-CoV-2 replication or infection in vitro and in vivo, (ii) an efficient mechanism for deleting this region from the viral genome may exist, given that the deletion variant is commonly detected after two rounds of cell passage, and (iii) the PRRA insertion, which is unique to SARS-CoV-2, is not fixed during virus replication in vitro These findings provide information to aid further investigation of SARS-CoV-2 infection mechanisms and a better understanding of the NSPRRAR deletion variant observed here.Important notes The spike protein determines the infectivity and host range of coronaviruses. SARS-CoV-2 has two unique features in its spike protein, the receptor binding domain and an insertion of twelve nucleotides at the S1/S2 boundary resulting a furin-like cleavage site. Here, we identified two deletion variants of SARS-CoV-2 that either directly affect the furin-like cleavage site itself (NSPRRAR) or a flanking sequence (QTQTN) and investigated these deletions in cell isolates and clinical samples. The absence of the polybasic cleavage site in SARS-CoV-2 did not affect virus replication in Vero or Vero-E6 cells. Our data indicate the PRRAR and its flanking sites are not fixed in vitro, thus there appears to be distinct selection pressures on SARS-CoV-2 sequences in vitro and in vivo Further investigation of the mechanism of generating these deletion variants and their infectivity in different animal models would improve our understanding of the origin and evolution of this virus.
Journal of virology
Guangdong Provincial Institution of Public Health, Guangzhou, China.