COVID-19 Virus Binds to Human Cells 1,000 Times Tighter Than Its Closest Relative

The new coronavirus appears to bind to human cells about 1,000 times tighter than its closest bat relative, researchers have found. In analyzing the structure of SARS-CoV-2, the virus that causes COVID-19, the team was able to better understand how it evolved and became so infectious to humans.

COVID-19 has now spread to almost every country in the world. There have been over 12 million confirmed cases and over 500,000 deaths, according to Johns Hopkins University. Scientists are trying to establish how and why the virus has been able to spread so far so quickly.

In a study published in Nature Structural & Molecular Biology, researchers led by Antoni Wrobel and Donald Benton, of the U.K.'s Francis Crick Institute, have now found the structure of the virus may play a role in how infectious it is. SARS-CoV-2, like other coronaviruses, has spikes coming out of it. These are proteins that help the virus enter a host cell.

They analyzed the spike protein of SARS-CoV-2 and compared it with the closest relative of the virus, a bat coronavirus called RaTG13. The spike of RaTG13 is over 97 percent similar to SARS-CoV-2.

Researchers discovered that the spike protein of the new coronavirus is much more stable than that of RaTG13. This makes it able to bind to human cells around 1,000 more tightly than the bat coronavirus.

"The spike is the entry key that allows SARS-CoV-2 into human cells," Wrobel said in a statement. "Changes in the virus' genome, which affect the spike's structure, therefore have potential to make the virus either more or less able to enter the host's cell. At some point in the evolution of this virus, it seems to have picked up changes, like the differences we found, which made it able to infect humans."

Where SARS-CoV-2 came from is unclear. Initial reports suggested the virus had passed from an animal to humans at a seafood market in Wuhan, China—the city where COVID-19 was first identified. That narrative is becoming less likely, however.

Research published in The Lancet showed some of the first people to become infected had no contact with the market. Other research also suggests the virus was circulating for months before the first cases were officially recognized.

What species of animal the virus came from is also unknown. It has been suggested a pangolin may have served as an intermediary host between bats and humans, but this has also been disputed by some scientists.

Researchers say their latest findings do not provide an insight into where the virus came from, but could give clues as to how it evolved. They say their findings indicate it is unlikely a bat virus similar to RaTG13 could infect humans.

Instead, SARS-CoV-2 may be the result of different viruses joining together and evolving through different host species. This could fit with the idea that one animal vector was infected with two coronaviruses at the same time, and in this host animal they combined.

Benton said researchers continue to try to work out how SARS-CoV-2 evolved and that the latest work will provide "a piece of this puzzle, as it suggests that the virus did not come straight from the bat coronaviruses currently known," he said.

CDC image of the coronavirus. The red spikes on the outside of the virus help the virus enter cells. CDC