The structures of the spike glycoproteins, which enable a virus to bind to and enter cells, for SARS-CoV-2 and the closely related bat virus RaTG13 are characterized in a paper in Nature Structural & Molecular Biology. The structures provide further information about how the SARS-CoV-2 spike evolved and may provide insights for vaccine design.
Bat coronaviruses have been identified as the likely evolutionary precursor to SARS-CoV-2, and previous studies have identified the bat virus RaTG13 as the closest known relative of SARS-CoV-2. However, it is not known how the virus evolved to infect humans nor whether this happened via an intermediary host or through direct transmission.
Antoni Wrobel, Donald Benton and colleagues compared the spike glycoproteins from SARS-CoV-2 and RaTG13. They found that, although the structures were similar, SARS-CoV-2 has a more stable form of the spike glycoprotein and is able to bind approximately 1,000 times more tightly to the human receptor protein ACE2. The authors also found that the presence of a furin cleavage site in the SARS-CoV-2 spike could be advantageous for the virus, as it may facilitate the virus binding to the receptor on cells. On the basis of their observations, the authors suggest that a bat virus similar to RaTG13 would be unlikely to infect human cells, which supports the theory that SARS-CoV-2 evolved from a recombination of distinct coronavirus genomes.
The authors note that their structure of the SARS-CoV-2 spike glycoprotein is presented in high resolution and is nearly complete, with more external loops than previously reported structures, which may provide important insights for vaccine design.
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