"Implications for the original SARS-CoV-2 animal source
... [E]ven if SARS-CoV-2 did originally arise from a bat precursor virus, which remains unproven, it must have spent considerable time in an intermediate animal host to allow it to adapt its S protein sufficiently to then be able to bind human ACE2. There are currently no explanations for how or where such a transition could have occurred to generate a SARS-CoV-2 spike protein optimised for human ACE2. Evidence of direct human infection by bat coronaviruses is rare, with transmission typically involving an intermediate host...
Does high human ACE2 binding affinity represent a recent gain-of-function mutation?
... Based on available genome sequence data, this study concluded that the current pandemic has been driven entirely by human-to-human transmission since at least December. As the SARS-CoV-2 structure employed in our studies was obtained from viruses collected early in the outbreak, it is not clear how the very first SARS-CoV-2 strains acquired such a high affinity for human ACE2 without prior exposure. These data suggest that SARS-CoV-2 spike RBD evolved by selection on a human-like ACE2."
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