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Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The spike protein that mediates SARS-CoV-2 entry into host cells, is one of the major targets for vaccines and therapeutics. Thus, insights into the sequence variations of S protein are key to understanding the infection and antigenicity of SARS-CoV-2. Here, we observed a dominant mutational variant at the 614 position of S protein (aspartate to glycine, D614G mutation). Using pseudovirus-based assay, we found that S-D614 and S-G614 protein pseudotyped viruses share a common receptor, human angiotensin-converting enzyme 2 (ACE2), which could be blocked by recombinant ACE2 with the fused Fc region of human IgG1. However, S-D614 and S-G614 protein demonstrated functional differences. First, S-G614 protein could be cleaved by serine protease elastase-2 more efficiently. Second, S-G614 pseudovirus infected 293T-ACE2 cells significantly more efficiently than the S-D614 pseudovirus, Moreover, 93% (38/41) sera from convalescent COVID-19 patients could neutralize both S-D614 and S-G614 pseudotyped viruses with comparable efficiencies, but about 7% (3/41) convalescent sera showed decreased neutralizing activity against S-G614 pseudovirus. These findings have important implications for SARS-CoV-2 transmission and immune interventions.
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