The researchers also discovered that a bat coronavirus recognizes the same human receptor as SARS-CoV-2, but the bat virus attaches to the human receptor rather poorly. However, a few mutations in the spike protein may have enhanced the ability of the bat virus to attach to the human receptor, leading to the bat virus jumping to humans and evolving to become SARS-CoV-2. Previous work by Li and others showed that one particular mutation allowed the 2002–2003 virus to get into human population; in the current work, it appeared that a number of mutations might be needed for SARS-CoV-2 to jump from bats to humans.
Also, two coronaviruses have been isolated from pangolins—a type of scaly, anteater-like mammal—in China. The researchers analyzed the structures of their spike proteins and found that one of the pangolin viruses could recognize the human receptor well, implying that pangolins might have helped the bat virus jump to humans by acting as intermediate hosts.
The researchers discovered that just a few mutations had made a molecular “ridge” in the spike protein more compact than a similar structure in the 2002-03 virus. This and other changes helped SARS-CoV-2 attach more strongly to the receptor.
cryo-electron microscopy: where protein molecules can be studied under ultra-cold temperature and inspected under an electron microscope.So the North Carolina author had working with the Wuhan virology lab already created a MOUSE-backbone Cov-Sars virus that infected mice. This one does not use a Mouse backbone
"This evidence for natural evolution was supported by data on SARS-CoV-2's backbone -- its overall molecular structure. If someone were seeking to engineer a new coronavirus as a pathogen, they would have constructed it from the backbone of a virus known to cause illness. But the scientists found that the SARS-CoV-2 backbone differed substantially from those of already known coronaviruses and mostly resembled related viruses found in bats and pangolins. "These two features of the virus, the mutations in the RBD portion of the spike protein and its distinct backbone, rules out laboratory manipulation as a potential origin for SARS-CoV-2" said Andersen." https://www.sciencedaily.com/releases/2020/03/200317175442.htm
"efforts to engineer a virus with the surface protein of the SHC014 coronavirus, found in horseshoe bats in China, and the backbone of one that causes human-like severe acute respiratory syndrome (SARS) in mice. The hybrid virus could infect human airway cells and caused disease in mice, according to the team’s results, which were published in Nature Medicine."https://www.the-scientist.com/news-opinion/lab-made-coronavirus-triggers-debate-34502
The lab coronavirus has a MOUSE "backbone" for the DNA. https://www.medicalnewstoday.com/articles/the-new-coronavirus-was-not-genetically-engineered-study-shows This article does not say MOUSE - but it should - why? I know because I read the actual science papers.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3372174/
The observation is that while SARS-CoV and closely related viruses from the civet can use ACE2 as a receptor,no bat coronavirus has been shown to use bat, human, or any other orthologs of ACE2(2, 27). Further, sequence-based studies of the coronaviruses that have been found in bats suggest that their RBDs contain deletions spanning key residues required for mediating contact with ACE2 (5, 15, 18, 20). These observations necessitated alternate models of SARS-CoV emergence, and the currently favored model is one in which a bat coronavirus recombined with the coronavirus of a second, unknown species to create a novel hybrid virus that can use ACE2 (20).
Additionally, we show that RaTG13, a bat coronavirus closely related to SARS-CoV-2, also uses hACE2 as its receptor. The differences among SARS-CoV-2, SARS-CoV and RaTG13 in Structural basis of receptor recognition by SARS-CoV-2
pdf link by Fang Li 2016
OK so the Pangolin is from Guangdong if it was an intermediary species host....
On a visit to Shaoguan, Guangdong province, last year, the Guardian and staff from CBCGDF saw a caged facility previously used for attempted breeding of the notoriously hard-to-breed pangolin.https://www.theguardian.com/environment/2020/feb/25/coronavirus-closures-reveal-vast-scale-of-chinas-secretive-wildlife-farm-industry
While there were no longer pangolin at the site, several locals near the facility confirmed the species had been raised there
They discovered that a bat coronavirus also binds to the ACE2 receptor, but poorly. A few mutations could have increased the ability of the bat virus to attach to the human receptor, allowing the hop to humans, according to the statement. The researchers also analyzed the structure of the spike proteins of pangolins, which could be an intermediate host between bats and humans, according to a previous Live Science report.https://www.livescience.com/why-coronavirus-attaches-stronger-human-cells.html
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