Mucus could Explain why SARS-CoV-2 doesn’t Spread Easily from Surfaces

From the ACS Press Room Mucus could Explain why SARS-CoV-2 doesn’t Spread Easily from Surfaces

“Mucins Inhibit Coronavirus Infection in a Glycan-Dependent Manner”

ACS Central Science

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 Science 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.

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 re-

searchers 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 corre-

Specific glycans (red squares in the illustration) on mucins can bind to coronavirus spike proteins, which could prevent viruses in cough or sneeze droplets from spreading from surfaces.

From the ACS Press Room

sponds 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.

“Bacteria Enzyme”

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Department of Energy, the Howard Hughes Medical Institute and the National Institutes of Health.

A bacterial enzyme (crystal structure shown here) makes a new type of biodegradable polymer, acholetin, which might someday find use in drug delivery, tissue engineering or other applications.

“Face Masks”

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masks would be only a minor source of PFAS in landfill leachates and domestic water. According to the researchers, this study should encourage the public to continue wearing face masks, especially during a pandemic. It could also help people make informed decisions about what type of masks to wear and encourage manufacturers to consider the chemicals used in masks, they explain. The authors acknowledge funding or support from the National Science Foundation, National Institutes of Health, Environmental Protection Agency, Department of Agriculture and the North Carolina Policy Collaboratory.

From the Editor

Last month, 56 students took part in the United States National Chemistry Olympiad (USNCO) local exam held at UTA . The section’s 11 nominees and their teachers for the national exam are on page 13. Good job, guys! And congratulations to the winners of the 2021 Doherty and Schulz awards: Mihaela C. Stefan, Doherty Award Heather Thompson, Schulz Award At first, I was most intrigued by the article on honeybee tongues. Although bees poke out their tongues to collect nectar and other water-based liquids; it seems that the hairs which cover the tongue are hydrophobic, not hydrophilic as previously suspected. So the liquids must be collected by capillary action between the hairs, right? Now I think I prefer the article on a previously unidentified bacterial enzyme that produces a newly described type of polysaccharide; this polymer, produced by Acholeplasma laidlawii, a common contaminant of laboratory cell cultures, has been named acholetin. Acholetin is similar in composition to chitin and to a biofilm-forming polysaccharide. Similar to chitin, it is a new type of biocompatible, biodegradable material. There is always something new to keep us all working and discovering...