Mucus could explain why SARS-CoV-2 doesn't spread easily from surfaces


Date:
March 2, 2022
Source:
American Chemical Society
Summary:
Early in the pandemic, many people fastidiously disinfected surfaces
because laboratory studies predicted that SARS-CoV-2 could be
easily transmitted in this way. Now, researchers have 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 could also
hint at why some people are more vulnerable to COVID-19 than others.



FULL STORY ========================================================================== Early in the pandemic, many people fastidiously disinfected surfaces
because laboratory studies predicted that SARS-CoV-2 could be easily transmitted in this way. Now, researchers reporting in ACS Central
Sciencehave 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 could also
hint at why some people are more vulnerable to COVID-19 than others.


========================================================================== Although experiments have shown that coronaviruses can persist on surfaces
for days or weeks, it is now apparent that SARS-CoV-2 is much more likely
to infect people through airborne droplets carrying the virus. The 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. With this in mind, Jessica Kramer and colleagues
wondered if 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 SARS-CoV-2 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.

For safety reasons, the researchers chose to study a human coronavirus
called OC43, which evolved relatively recently from a cow coronavirus and causes mostly mild respiratory infections. The team deposited droplets
of the virus in buffer or growth medium supplemented with 0.1-5% mucins,
which corresponds to the concentration range of mucins found in nasal
mucus and saliva, onto a plastic surface and let the drops dry. Then,
they rehydrated the viral residue and measured its ability to infect
cells. In comparison to the buffer or growth medium alone, the solutions supplemented with mucins were dramatically less infectious. The team also tested steel, glass and surgical mask surfaces, finding similar results.

The researchers showed 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 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, they say.

The authors acknowledge funding from the National Science Foundation.

========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Casia L. Wardzala, Amanda M. Wood, David M. Belnap, Jessica
R. Kramer.

Mucins Inhibit Coronavirus Infection in a Glycan-Dependent
Manner. ACS Central Science, 2022; DOI: 10.1021/acscentsci.1c01369 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220302110610.htm

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