Why SARS-CoV-2 Spread So Easily Among People?

Researchers have identified microscopic features that may make this pathogen more infectious than the SARS virus and can serve as drug targets.
BUFFALO, N.Y. - Sept. 2, 2020 - PRLog -- With nearly 100,000 people infected with SARS-CoV-2 worldwide, researchers are racing to understand what makes it so easy to spread.

Several genetic and structural analyses have identified a key feature of this virus—a protein on the surface—which may explain why it is so susceptible to infect human cells.

"Understanding the spread of the virus is key to control and future prevention," says David Veesler, a structural virologist at the University of Washington in Seattle, who released his team's findings on viral proteins on the biomedical preprint server bioRxiv on February 20.

The SARS-CoV-2 spreads much easier than the virus that causes severe acute respiratory syndrome (SARS),  and infects more than ten times as many people as SARS.

Stinging intruder

To infect cells, coronaviruses use a "spike" protein (S protein) to bind to the cell membrane, and the process is activated by specific cellular enzymes. Genomic analysis of this novel coronavirus showed that its peak protein was different from those of close relatives and showed that there was a site on this protein that was activated by a host cell enzyme called flynase.

Several other groups have also identified this activation site and believe that it may enable the virus to spread effectively between humans. They point out that these sites are also present in other viruses that are easily transmitted from person to person, including severe influenza virus strains. On these viruses, the activation site is on a protein called hemagglutinin, not on spike proteins.

Calls for caution

Other scientists are cautious about comparing the activation site of influenza viruses with that of SARS-CoV-2 (https://www.creativebiomart.net/SARS-CoV-2-Proteins-and-T...). Peter White, a virologist at the University of New South Wales in Sydney, Australia, says the hemagglutinin protein on the surface of the influenza virus is neither similar nor related to the peak protein of the coronavirus.

Drug Target

McLellan's team in Texas discovered another feature that could explain why SARS-CoV-2 was so successful in infecting human cells. Their experiments showed that this S protein binds to an receptor on human cells, angiotensin-converting enzyme 2 (ACE2 (https://www.creativebiomart.net/symbolsearch_ACE2.htm)), at least ten times more tightly than the S protein in the SARS virus. This was also found by Veesler's team, suggesting that the recipient is another potential target for vaccines or therapies. For example, a drug that blocks the receptor may make it harder for coronaviruses to enter cells.

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