We know it best as a stringy slime dripping from noses and as viscous, discolored goop hacked up by sickened airways. But it’s so much more than that. Coating the surfaces of guts, eyes, mouth, nasal cavity and ears, mucus plays a range of important physiological roles — hydrating, cleaning, supporting good microbes and warding off foreign invaders.
“I like to call it the unsung hero of the body — it’s something that has such powerful effects over our health,” says Katharina Ribbeck, a biophysicist at MIT who with colleagues outlined the many roles of mucus in the 2018 Annual Review of Cell and Developmental Biology. Most of those functions come from the 5 percent of the substance that’s not water: various salts, lipids and proteins, most notably mucins, which give mucus its gel-like qualities — long, thread-like polypeptides coated in covalently bound chains of sugars called glycans.
Scientists have uncovered many ways that mucin proteins work to keep body surfaces clean and protected, and are continuing to parse the complex interactions the molecules have with microbes. Here’s some of what they’ve learned so far, and where the research is heading.
A Multitude of Mucins
Mucosal coatings vary considerably across the body, in line with needed functions. The eye, for example, is covered with a thin film of not especially viscous mucus, sufficient to keep it hydrated. The inside of the colon, in contrast, bears a thick, gummy coating that stops bacteria from sneaking through.
