"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."
Open Access - This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.
To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.