Novel Coronavirus SARS-CoV-2 Spike Protein.
This small addition might also explain how the coronavirus, SARS-CoV-2, can be transmitted from person to person early on, before symptoms set in — making it so deadly it could spur a pandemic that has killed hundreds of thousands of people.
Then, an enzyme — a substance that, in this case, sits on a human cell and causes a reaction — called furin cuts the loop, splitting the tip of the spike away from the stalk and the rest of the virus.
The loop of protein may help explain how differently SARS-CoV-2 infects humans compared to SARS, its closest human-infecting relative.
New research suggests that the protein loop found on SARS-CoV-2 is essential to its ability to infect human lung cells.
A May paper published by German researchers in the journal Molecular Cell found that mutant versions of the novel coronavirus without the furin-targeted loop were unable to infect lung cells.
While SARS-CoV-2 most resembles a coronavirus found in bats, Racaniello noted that bat viruses don’t have a loop that’s cleaved by furin.
A similar proposed COVID-19 treatment blocks a different enzyme called TMPRSS2, which chops up the spike protein even more in the very last stages as the coronavirus RNA invades the human cell.
An even more recent study of the SARS-CoV-2 spike from Whittaker and colleagues, which is still under review by the iScience journal, found that many more cellular enzymes than just furin can cut the loop and allow the coronavirus to invade cells.
That adaptability — using whatever is available to start attacking cells — may partly explain why the novel coronavirus seems to infect nose and throat cells richer in these other enzymes more easily than SARS does.
Some scientists disagree that the spike protein loop is the key to the infectiousness of SARS-CoV-2.
The new bat virus, dubbed RmYN02, is 93.3% genetically identical to SARS-CoV-2 — but its spike tip doesn’t recognize the same receptor on human cells, making it harmless to people.
In reality, finding a loop cut by furin in a virus “is like opening a book to a random page and finding the word ‘the’ in it — not very surprising,” University of Nebraska bioinformatics expert Kate Cooper told BuzzFeed News
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