Early in the pandemic, many people disinfected surfaces fiercely because some lab studies predicted that the coronavirus could be easily transmitted by the surface
But the reality is that coronavirus is much more likely to infect people through airborne droplets carrying the virus.
In a new study, researchers found a possible explanation for why the predictions didn’t pan out.
Sugar-decorated proteins in mucus could bind to the coronavirus on surfaces, keeping it from infecting cells.
The findings also reveal why some people are more vulnerable to COVID-19 than others.
Previous surface studies have shown that coronaviruses can persist on surfaces for days or weeks.
These surface studies typically used viruses suspended in buffers or growth media, whereas in the real world, SARS-CoV-2 is coated in mucus when someone coughs or sneezes.
Researchers wanted to know whether mucus components could explain the discrepancy between the lab predictions and reality.
In addition to water, salts, lipids, DNA, and other proteins, mucus contains proteins called mucins, which are heavily modified with sugar molecules known as glycans.
To infect cells, the coronavirus spike protein binds glycan molecules with sialic acid at their ends on the cell surface.
So, the researchers wondered if the coronavirus also recognizes sialic acid-containing glycans in mucins.
If the spike protein is already bound to glycans in mucus, perhaps it couldn’t bind to the ones on cells, they reasoned.
In the current study, the team examined a human coronavirus called OC43, which evolved relatively recently from a cow coronavirus and causes mostly mild respiratory infections.
They found that as the droplets dried, mucins moved to the edge and concentrated there in a coffee-ring effect, bringing the virus with them.
This brought mucins and virus particles close together, where they could more easily interact.
Cutting off sialic acid glycans from mucins with an enzyme eliminated viral binding and destroyed the glycoproteins’ protective effect.
Because coronavirus (SARS-CoV-2), like OC43, binds to sialic acid glycans on cell surfaces, mucins would also likely reduce its infectivity, the researchers suspect.
The levels and types of sugar molecules on mucins can vary with diet and certain diseases, which could possibly explain the vulnerability of certain people to COVID-19.
If you care about COVID, please read studies about new risk factor for severe COVID-19, and new antibody treatment for COVID-19.
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The study was conducted by Casia L. Wardzala et al., and published in ACS Central Science.
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