A key piece of the #COVID19 #SARSCoV2 origin puzzle emerges: where did the virus's unusual spike protein RBD—the receptor-binding domain that engages human ACE2 protein and allows the virus to enter human cells—come from? A new study from Shen & coworkers provides an answer.(1/5)

The authors isolated coronaviruses from pangolins dying from respiratory disease in a wildlife rescue center in Mar-Aug 2019. One CoV-positive pangolin had antibodies that cross-reacted with #SARSCoV2 antigens, suggesting the animal was infected with a SARS-CoV-2-like virus.(2/5)

The pangolin #coronavirus was highly similar to #SARSCoV2 in several key proteins, including a remarkably similar spike protein RBD that differs from the SARS-CoV-2 RBD at only ONE amino acid position out of ~457 amino acids. (3/5)

Thus #SARSCoV2 novel RBD may have originated from recombination between a bat #coronavirus such as RaTG13, which is 96% identical to SARS-CoV-2, and a pangolin CoV: "A virus related to Pangolin-CoV... appears [to have] donated the RBD to SARS-CoV-2". (4/5) https://www.nature.com/articles/s41586-020-2313-x_reference.pdf

While the pangolin coronavirus was too different from #SARSCoV2 to be the native host of the #COVID19 virus, these findings strengthen a model in which bat and pangolin coronaviruses recombined to give rise to SARS-CoV-2. Thank you, @SchreiberStuart for the heads-up! (5/5)

Also, now no conspiracy theory is needed to explain where the novel and brutally effective RBD (Kd=~5-30 nM to human ACE2 for RBD or whole spike protein) of #SARSCoV2 could come from—a #coronavirus that infects another animal species evolved a virtually identical RBD!